METHOD AND APPARATUS FOR PRODUCTION OF HELICAL SPRINGS BY SPRING WINDING

Abstract

A method produces helical springs by spring winding with a numerically controlled spring winding machine, a wire is fed, controlled by an NC control program, through a feed device to a forming device of the spring winding machine and is formed with the aid of tools in the forming device to form a helical spring. A measurement time is defined which occurs in a final phase of an overall manufacturing time for the helical spring at a time period before the end of the overall manufacturing time. A position of a spring end which is formed by an end surface of the wire is measured at this measurement time to determine an actual angle position of the spring end. A remaining distance for the wire feed is then calculated to achieve a nominal angle position of the spring end, as intended for the helical spring, at a reference time which occurs at a later time and the wire is fed through the remaining distance. The method allows the relative angle position of the spring ends of a helical spring to be set very precisely.

Description

RELATED APPLICATION

This application claims priority of German Patent Application No. 10 2010 014 386.3, filed on Apr. 6, 2010, the subject matter of which is incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to methods for production of helical springs by spring winding with a numerically controlled spring winding machine, and to spring winding machines suitable for carrying out the method.

BACKGROUND

Helical springs (also denoted as coil springs) are machine elements required in large quantities and different configurations in numerous fields of application. Helical springs, which are also referred to as wound torsion springs, are normally produced from spring wire and are in the form of tension springs or compression springs depending on their load during use. Compression springs, in particular bearing springs, are required, for example, in large quantities for automobile construction. The spring characteristic can be influenced, inter alia, by sections of different pitch or with different pitch profiles. For example, in the case of compression springs, there is frequently a central section of greater or lesser length with a constant pitch (constant section) adjacent to which, at both ends of the spring, there are contact areas with a pitch which becomes less towards the ends. In the case of cylindrical helical springs, the spring diameter is constant over the length of the springs, but it may also vary over the length, for example, in the case of conical or barrel-shaped helical springs. In addition, the overall length of the (unloaded) spring may vary widely for different applications.

Nowadays, helical springs are normally produced by spring winding with the aid of numerically controlled spring winding machines. In this case, a wire (spring wire) is fed, controlled by an NC control program, by a feed device to a forming device of the spring winding machine, and formed with the aid of tools of the forming device, to form a helical spring. The tools generally include one or more variable-position winding pins to fix and possibly to vary the diameter of spring turns and one or more pitch tools which govern the local pitch of the spring turns in each phase of the manufacturing process.

Spring winding machines are generally intended to produce a large number of springs with a specific spring geometry (nominal geometry) within very narrow tolerances, at a high rate. The functionally important geometry parameters include, inter alia, the relative angle position of the spring ends at the opposite end areas of the helical spring. In this context, the term “spring end” denotes the end surface of the wire which forms the helical spring, which end surface is produced by a shearing process. Errors in the relative angle position of the spring ends can lead to errors in the block size (length in the completely compressed state), in the spring length of the unloaded spring, in the spring force and in the grinding pattern of the spring end faces.

To comply with stringent quality requirements, for example, in the automobile field, it is normal practice to measure certain spring geometry data, for example, the diameter, length, pitch, and/or pitch profile of the spring, and/or the relative angle position of the spring ends at both ends of the helical spring after completion of a spring and to automatically sort the finished springs depending on the result of the measurement, into satisfactory parts (spring geometry within the tolerances) and unsatisfactory parts (result outside the tolerances), and possibly into further categories. This procedure is highly uneconomic, in particular in the case of long springs since, in the case of long springs, a relatively great length of wire is consumed for each spring and must be thrown away if it is found that the finished spring is outside the tolerances.

It has already been proposed for the diameter, length and pitch of the spring to be checked by suitable measurement means during manufacture, and for manufacturing parameters to be changed in the event of any discrepancies outside tolerance limits such that the spring geometry remains within the tolerances. DE 103 45 445 B4 discloses a spring winding machine which has an integrated measurement system with a video camera which is directed at that area of the spring winding machine in which the forming of the spring starts. An image processing system connected to the video camera and having appropriate evaluation algorithms is intended to allow the diameter, length and pitch of the spring to be checked during manufacture, and it is intended to be possible to vary these spring geometry parameters by feedback to the processing tools, which can be adjusted by motors, during manufacture. An evaluation algorithm for determining the current spring diameter is described in detail.

The relative angle position or angular position of the spring ends with respect to one another can also fluctuate greatly as a function of material characteristics of the wire and of the geometry of the spring. One known method for limiting severe scatters in the relative angle position uses a measurement probe which produces a measurement signal when the front spring end (that which is produced firstly) of the developing spring reaches a specific position at a time before the end of the overall manufacturing time, the angular distance of which (along the turns) to the desired nominal angle position at the end of the total manufacturing time is known. There is a defined remaining distance between the response position of the measurement probe, which the measurement system knows in advance, and the nominal position of the spring end which is desired at the end of the manufacturing process, measured along the profile of the turns, and this remaining distance is constant for all helical springs for the manufacturing process that has been set out. The wire feed control is programmed such that a wire feed which is taking place is interrupted when the measurement probe responds, and the preprogrammed constant remaining distance at the wire feed is then also moved through, as a result of which the spring end then reaches the desired nominal angle position. Mechanical measurement probes with a variable stop and optical measurement probes have already been used, which use a laser to determine that the monitored angle position at the spring end has been reached. Measurement systems with measurement probes such as these generally have a complex design.

It could therefore be helpful to provide a method and an apparatus of a generic type such that, particularly when producing relatively long helical springs, helical springs can be produced within tight geometric tolerances with high reliability, composed of wire materials of widely differing quality. It could also be helpful to provide for the production of long helical springs with little scatter of the relative angle position of the spring ends.

SUMMARY

We provide methods of producing helical springs by spring winding with a numerically controlled spring winding machine including feeding a wire controlled by an NC control program through a feed device to a forming device, forming the wire into a helical spring in the forming device, defining a measurement time which occurs in a final phase of an overall manufacturing time for the helical spring at a time period before the end of the overall manufacturing time, measuring a position of a spring end formed by an end surface of the wire to determine an actual angle position of the spring end at the measurement time, determining a remaining distance for the wire feed required to achieve a nominal angle position of the spring end, as intended for the helical spring, at a predefined reference time which occurs at a time after the measurement time, and feeding the wire through the remaining distance.

We further provide spring winding machines that produce helical springs by spring winding under the control of an NC control program including a feed device and a forming device that receives wire from the feed device and includes at least one winding tool which controls diameter of the helical spring at a predeterminable position, and at least one pitch tool whose action on a helical spring being produced controls a local pitch of the helical spring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic overview illustration of one example of a spring winding machine with parts of the feed device and of the forming device.

FIG. 2 shows a perspective illustration of fittings for the spring winding machine as shown in FIG. 1 including two cameras of a camera-based, optical measurement system for contactless real-time recording of data relating to the geometry of a spring which is currently being produced, and a spring guide device.

FIG. 3 shows the situation illustrated in FIG. 2 viewed from a direction parallel to the optical axis of the camera optics of the second camera.

FIG. 4 shows an enlarged illustration of a detail of the field of view of the second camera when the actual angle position of the spring end is being measured at a measurement time before the end of manufacture.

FIG. 5 shows an enlarged illustration of a detail of the field of view of the second camera when the spring length is being measured at a measurement time after the end of manufacture.

FIG. 6 schematically illustrates an axial view of the free spring end section of a helical spring to explain a correction method for determining the actual angle position of the spring end.

FIG. 7 shows a calculation scheme for determining the sought arc length be in the course of the correction method.

DETAILED DESCRIPTION

It will be appreciated that the following description is intended to refer to specific examples of structure selected for illustration in the drawings and is not intended to define or limit the disclosure, other than in the appended claims.

We provide methods for production of helical springs by spring winding with a numerically controlled spring winding machine, the method comprising:

• • feeding a wire controlled by an NC control program through a feed device to a forming device of the spring winding machine; and
  • forming the wire into a helical spring with the aid of tools in the forming device;
  • defining a measurement time which occurs in a final phase of an overall manufacturing time for the helical spring at a time period before the end of the overall manufacturing time;
  • measuring a position of a spring end, which is formed by an end surface of the wire, to determine an actual angle position of the spring end at the measurement time;
  • calculating a remaining distance for the wire feed required to achieve a nominal angle position of the spring end, as intended for the helical spring, at a predefined reference time which occurs at a time after the measurement time; and
  • feeding the wire through the remaining distance.

There is also provided a spring winding machine configured to perform the method.

In the method, a measurement time is defined which occurs in the final phase of the overall manufacturing time required for the manufacture of a complete helical spring at a time period before the end of the overall manufacturing time of the individual spring, that is to say at a time before the end of the process of manufacturing a spring. At the measurement time, the position of the spring end, which is defined by the end surface of the wire, is measured to determine an actual position of the spring end at the measurement time. A remaining distance is calculated on the basis of the result of this measurement through which the wire still has to be fed or fed forward with the aid of the feed device until a nominal angle position of the spring end, which is predetermined for the helical spring, is reached at a predefined reference time which occurs at a time after the measurement time. The wire is then fed forward with the aid of the control system through this calculated remaining distance.

The reference time may correspond to the end of the overall manufacturing time. In these cases, the opposite spring end can be produced immediately when the reference time is reached in that a cutting device is used to separate the helical spring that has been produced from the fed wire. This is generally provided when only a constant section, that is to say a section with a constant pitch, without any pitch change is manufactured after the reference time before the spring is cut off from the wire, that is to say for an open spring end section.

The reference time may also be an intermediate time which occurs at a time before the end of the overall manufacturing time. This is generally used when an end section with a pitch change is also manufactured after the reference time, in particular a contact section with a pitch which decreases to the spring end to create an end with touching turns. Thus, in this case, the movement through the remaining distance is also followed by a final part of greater or lesser duration of the manufacturing time. This final part is specific for the spring geometry of one spring batch and is preset as being fixed in the control program and is, therefore, constant. The final part is normally sufficiently short in comparison to the overall manufacturing time that no or scarcely any angle position errors can build up.

Depending on the length of the spring, there is in any case a remaining time between the measurement time and the end of manufacture which, for example, may be more than about 5%, more than about 10%, more than about 20% or more than about 30% of the overall manufacturing time.

The term “time” in this application means a specific point within the NC control program, that is to say a program time or a time within the program sequence. A “time period” is correspondingly a period between program times of a program-time function. To this extent, a program time corresponds to a sequence position in the sequential process of program steps while the program is being processed. For example, if a trigger signal is required to operate a measurement device in a specific phase of processing the program, this trigger signal can be triggered by a program line that occurs at an appropriate point. This allows a “measurement time” to be defined in the program. In the program, signals such as these are directly linked to specific positions of the machine axes, for example, to the machine axis of the wire feed and/or to the machine axis for the position of the pitch tool. A “time” in a program-time function therefore corresponds to a point on the movement curve of one or more machine axes. A program-time function results in times (program times) within an NC program synchronized to the progress of the spring production. To this extent, the program-time function is also a movement function with respect to the movements of machine axes. In particular, a program-time function also corresponds to a movement function of the wire feed.

In the prior art methods, the response position of a measurement probe predetermines a location of the observed spring end, and a constant remaining distance is moved through starting from this location. In our methods, a measurement time is predetermined and a remaining distance for the remaining forward feed results in a variable form and individually for each spring as a function of the angle position of the spring end detected at the measurement time, which is referred to as the “actual angle position.”

With respect to the control program, the difference can be described by stating that, in conventional methods, the time of response of the measurement probe with respect to a position in the NC control program is variable, but the remaining distance is constant. In contrast, in our methods, the position at the measurement time is constant or predetermined in a fixed manner in the NC control program, while in contrast, the remaining distance is variable and results individually for each spring only from the calculation on the basis of the measured actual angle position, or the actual angle position derived from the measurement.

There is no need for optical or mechanical measurement probes of complex design. We also avoid the adjustment effort associated with the use of such devices, thus considerably simplifying the handling. Some measurement probes are also susceptible to defects. In the case of thin wires, electromechanical probes, for example, are occasionally used, which close an electrical circuit by touching contact when they touch the spring end. We avoid the contact problems occasionally observed in this case.

Preferably, a camera with a two-dimensional field of view is used for measurement and the camera arranged such that the end section of the spring with the spring end lies within the field of view at the measurement time. Measured values can then be determined with the aid of an image processing system associated with the camera. Some conventional spring winding machines already have suitable measurement cameras to measure the overall length of the finished spring, its diameter and/or other geometric data which can be defined in the end area of the spring after the end of manufacture. It may be possible to use these cameras for a new measurement task. This makes it possible to save the design complexity required for conventional measurement probes.

The measurement can also be carried out by other measurement means. By way of example, a laser system can be used for measurement.

An arrangement of the camera with the observation direction in the longitudinal direction of the spring is possible to record and evaluate images of the end face of the helical spring with the spring end. However, this may obstruct the operation of the spring winding machine. Inter alia, it is therefore preferable for the camera to be arranged alongside the position in which the helical spring can be expected or alongside the movement to be traveled by the helical spring, and for an observation direction of the camera to be aligned transversely, in particular at right angles, to the alignment of the longitudinal axis of the helical spring during spring manufacture. The end section with the spring end can then be recorded in a side projection, in which the spring end then normally represents a step with greater or lesser curvature, depending on the angle position.

In one method for determining the actual angle position of the spring end at the measurement time, a distance value is determined for a distance, which is measured, for example, at right angles to the longitudinal axis of the spring between a tangent to an external contour of a turn of the helical spring and a projection of the spring end in the field of view. Since the spring end is normally displayed as a clearly defined contour with greater or lesser curvature in the side projection, a distance measurement such as this can be carried out using known distance determining tools in an image processing system with high precision and within a short time.

In one method, which provides particularly precise measured values, a relative orientation of the spring end is determined at the measurement time with respect to an observation direction, and the value for the distance value is corrected as a function of the orientation. This makes it possible to take account of projection effects which can have a disadvantageous effect on the measurement accuracy, particularly when the wire diameter is relatively large.

The timing of the measurement time with respect to the spring geometry is preferably configured such that in a remaining time interval which is required to move through the remaining distance, that is to say in the time between the measurement time and the intermediate time or the end of manufacture at least one turn of the helical spring is also produced, with the remaining time interval preferably being sufficiently long that between one turn and three turns of the spring are also produced while moving through the remaining distance. Such remaining time intervals are on the one hand long enough to move through the calculated remaining distances with sufficient accuracy, while on the other hand they are sufficiently short to avoid an error in the position of the spring end at the end of the manufacturing process resulting over the remaining distance, for example, because of wire quality fluctuations.

In some of our methods, the feed movement of the wire is briefly interrupted to carry out the measurement such that the spring end to be measured is stationary at the measurement time. This allows measurements with high measurement accuracy, and the remaining distance to be moved through after continuation of the feed movement can be taken into account with little effort in the control of the machine. It is also possible to carry out the measurement while the wire is being fed continuously and to correct the remaining distance determined from the measurement by a component which results between the detection of the spring end at the measurement time and the consideration of the measurement result in the machine control system.

Preferably, at least one further measurement is carried out after the end of manufacture and before the helical spring is cut off from the fed wire. By way of example, this further measurement can be used to determine the overall length of the finished helical spring and/or its diameter and/or other geometric parameters. Alternatively or additionally, it would also be possible to use the further measurement to determine the actual angle position of the spring end at the end of the overall manufacturing time to check the success of the method.

Both measurements can be carried out using the same measurement means, in particular using the same camera since the position of the spring end at the measurement time which occurs before the end of manufacture, and the position of the spring end at the end of the overall manufacturing time are normally not far apart from one another, that is to say only one or a few turns.

We also provide numerically controlled spring winding machines specially configured to carry out the method. These machines have a feed device for feeding wire to a forming device as well as a forming device with at least one winding tool which essentially governs the diameter of the helical spring at a predeterminable position as well as at least one pitch tool whose action on the developing helical spring determines the local pitch of the helical spring.

The spring winding machine preferably has a camera positioned at a distance from the forming device such that a free spring end section runs into the coverage area of the camera in a final phase of the production of the helical spring. When using a camera with a sufficiently large coverage area, the camera can be used for a plurality of spring end measurements which can be carried out successively in time.

In some modern CNC spring winding machines which already have a suitable measurement system with a camera, our methods can be implemented subject to already existing design preconditions. We provide the capability of implementing additional program parts or program modules, or a program change in the control software of computer-aided control devices.

We further provide computer program products stored in particular on a computer-readable medium or in the form of a signal, wherein the computer program products result in the computer carrying out our methods or preferably to products loaded in the memory of a suitable computer and run by a computer.

These and further features are disclosed not only in the appended claims, but also in the description and the drawings, wherein the individual features can in each case be implemented on their own or in groups of two or more in the form of sub-combinations and in other fields.

Turning now to the drawings, the schematic overview illustration in FIG. 1 shows major elements of a CNC spring winding machine 100 based on a known design. The spring winding machine 100 has a feed device 110 equipped with feed rollers 112 and feeds successive wire sections of a wire 115 which comes from a wire supply and passes through a directing unit with a numerically controlled feed rate profile into the area of a forming device 120. The wire is formed with the aid of numerically controlled tools in the forming device to form a helical spring. The tools include two winding pins 122, 124 arranged offset through an angle of 90° aligned in the radial direction with respect to the center axis 118 (corresponding to the position of the desired spring axis), and determine the diameter of the helical spring. The position of the winding pins can be varied for basic adjustment for the spring diameter during the setting-up process along the movement lines shown by dashed-dotted lines and in the horizontal direction (parallel to the direction in which the wire is introduced) to set the machine up for different spring diameters. These movements can also be carried out with the aid of suitable electrical drives monitored by the numerical control system.

A pitch tool 130 has a tip aligned essentially at right angles to the spring axis and engages in the developing spring alongside the turns. The pitch tool can be moved with the aid of a numerically controlled movement drive for the corresponding machine axis parallel to the axis 118 of the developing spring (that is to say at right angles to the plane of the drawing). The wire which is fed forward during spring production is forced in a direction parallel to the spring axis by the pitch tool corresponding to the position of the pitch tool, with the local pitch of the spring in the corresponding section being governed by the position of the pitch tool. Pitch changes are produced by moving the pitch tool parallel to the axis during spring production.

The forming device has a further pitch tool 140 which can be supplied vertically from underneath and has a wedge-shaped tool tip inserted between adjacent turns when the pitch tool is being used. The adjustment movements of the pitch tool run at right angles to the feed direction. The pitch tool is not used in the illustrated production process.

A numerically controllable separating tool 150 is fitted above the spring axis and cuts the helical spring that has been produced off from the wire supply being fed with a vertical working movement after completion of the forming operations. In FIG. 1, the wire which has been fed is shown in a situation immediately after the previously completed helical spring has been cut off. In this position, the wire has already formed half a turn and the wire end which forms the spring start is located 0.3 turns before the position of the pitch tool 130.

The machine axes of the CNC machine which belong to the tools are controlled by a computer-numerical control device 180 which has memory devices in which control software resides including, inter alia, an NC control program for the working movements of the machine axes.

To manufacture a helical spring, starting from the “spring complete position” shown, the wire is fed in the direction of the winding pins 122, 124 with the aid of the feed device 110, and is deflected by the winding pins to the desired diameter, forming a curve in the form of a circular arc until the free wire end reaches the pitch tool 130. When the wire is fed further, the axial position of the pitch tool determines the current local pitch of the developing helical spring. The pitch tool is moved axially under the control of the NC control program when it is intended to change the pitch during spring development. The actuating movements of the pitch tool essentially govern the pitch profile along the helical spring.

When setting up the spring winding machine, the forming tools are moved to their respective basic settings. In addition, the NC control program is created or loaded, controlling the actuating movements of the tools during the manufacturing process. The geometry input for the spring winding machine is carried out by an operator on the display and control unit 170 which is connected to the control device 180.

A number of fittings which are advantageous for implementation of the method for the spring winding machine as shown in FIG. 1 will now be explained with reference to FIG. 2. The elements from FIG. 1 are annotated with the same reference symbols as in FIG. 1. FIG. 2 shows the spring winding machine during the production of a relatively long, cylindrical helical spring 200 of which approximately 20 turns have already been produced at the time shown in the figure. This is a long spring with an L/D ratio between the overall length L of the completed spring and the diameter D of the spring of more than ten. To ensure that the spring, which becomes ever longer as the wire feed increases, remains straight and that its free end does not bend downwardly, a spring guide device 210 is provided. The spring guide device has an angle plate 212, which is attached with an approximately horizontal longitudinal axis to the frame of the spring winding machine, and has a V-shaped profile. The flat inclined surfaces of the angle plate which run together downward support the spring at the bottom and at the side such that the longitudinal axis (central axis) of the developing spring runs coaxially with respect to the center axis 118 of the developing spring. The angle plate is attached to the machine frame with a holding device, which is not shown, and it can be adjusted in height and in lateral direction to allow the desired guidance, coaxial with respect to the center axis 118 of the spring, for springs of different diameter. After completion of the process of manufacturing a spring, the angle plate can automatically be pivoted downwardly by a hydraulic pivoting drive to allow the finished spring to slide into a collecting container.

That end of the angle plate which faces the forming device is located with a clear separation of a few centimeters away from the forming device such that a fully floating spring section 202 remains between the tools of the forming device and the machine-side start of the angle plate. The length of the angle plate is matched to the overall length of the finished helical spring such that the spring end section manufactured first projects freely beyond that end of the angle plate which is remote from the machine during the final manufacturing phase. The freely floating spring section 202 close to the machine and the spring end section 204 remote from the machine are thus accessible for an optical measurement with an observation direction at right angles to the longitudinal axis of the helical spring.

The spring winding machine is equipped with a camera-based, optical measurement system for contactless real-time recording of data relating to the geometry of a spring currently being produced. The measurement system has two identical CCD video cameras 250, 260 which, in the example, with a resolution of 1024×768 pixels (image elements) can supply up to 100 images per second (frames per second) via an interface to a connected image processing system. The recording of the individual images is in each case triggered via trigger signals from the control system. This defines the measurement times. The image processing software is accommodated in a program module which interacts with the control device 180 for the spring winding machine, or is integrated therein.

Both cameras are mounted on a mounting rail 255 which is resistant to twisting and attached at the side to the machine frame of the spring winding machine, adjacent to the spring guide device in the area of the guide rollers of the feed device such that the longitudinal axis of the mounting rail runs parallel to the machine axis 118. The measurement cameras can be moved longitudinally on the mounting rail and can be fixed at any desired selectable longitudinal positions.

The first camera 250, which is close to the machine, is fitted such that its rectangular field of view covers a part of the freely floating spring section 202 at a distance from the forming tools.

The second camera 260 is intended to record the free spring end 204 and therefore positioned on the mounting rail such that the free spring end runs into the coverage area of the second camera during the final phase of production of the helical spring.

An illumination device is fitted at the height of the axis 118 diametrically opposite the cameras, providing illumination in the form of a flash at the measurement times predetermined by the control system and as a reaction to trigger signals from the control system, allowing transmitted-light measurement. A front-lighting device can be provided on the side of the cameras to improve the visibility of interesting details of the spring for measurement.

FIG. 3 shows the situation illustrated in FIG. 2 from a viewing direction parallel to the direction of the wire feed (C axis of the spring winding machine) or parallel to the optical axis of the camera optics of the first camera. A section through the wire 115 can be seen on the left, which is fed in the feed direction (at right angles to the plane of the drawing) to a curved inclined surface of the lower winding tool 124. The winding tool forces the wire upwardly onto a path which is curved in a circular shape in the direction of the upper winding tool, and in the process the wire is permanently formed. The tip of the pitch tool 130 can be seen above the winding tool, and a side working surface of the tip rests on the developing turn. The pitch tool can be moved parallel to the spring axis 118 (in the direction of the arrow) under NC control with the aid of the associated machine axis such that the local pitch of the spring at the forming location is governed by the position of the pitch tool.

In FIG. 3, solid lines show a situation in the final phase of manufacture of a cylindrical helical spring 200, which has an end contact section 206, which has already been produced, with a continuously increasing pitch, followed by a constant section 208 with a constant pitch and an opposite contact section, which has not yet been manufactured at the illustrated time, with a decreasing pitch. The manufacturing process has not yet been completed at the illustrated time, and some turns (for example, between 1 and 5) still need to be produced. However, the manufacturing process has already advanced so far that the free spring end section 204 has already passed the angle plate 212 of the spring guide device and projects freely from the machine side into the rectangular field of view 262 of the second camera.

A smaller rectangular measurement area 264 can be seen within the rectangular field of view 262 of the second camera 260, which includes the area of the free spring end section 220 and the turn sections which are located vertically above and below this in the image with a high point 224 and low point 266 which appear to be curved in a semicircular shape. The free spring end section is bounded at the end by the end surface 222 of the wire 115. This more or less planar end surface was produced in a shearing process by the cutting apparatus after completion of the manufacture of the previous spring, and is also referred to in this application as the “spring end.”

FIG. 4 shows an enlarged illustration of the situation shortly before the end of manufacture.

The dashed lines in FIG. 3 show the same spring at a later time after completion of the overall manufacturing time, but before cutting off from the wire supply. The field of view of the camera is sufficiently large that both situations can be covered in the same field of view with the same camera setting.

FIG. 5 shows an enlarged illustration of the situation after the end of manufacture. The free end section of the spring is in this case enclosed by a different rectangular measurement area 266 which can be activated in the same field of view, but is not illustrated in FIG. 3 for clarity reasons.

The measurement areas 264 and 266 represent measurement tools in the image processing system connected to the camera. The image content can be analyzed with the aid of these tools, for example, to determine geometric data.

During large-scale manufacture of helical springs, the following procedure can be used with this spring winding machine. First, the desired nominal geometry of the helical spring is entered on the display and control unit 170, or appropriate already available geometric data is loaded from a memory of the spring winding machine, for example, by inputting an identification number. A so-called “NC generator” uses the geometric data to calculate an NC control program, whose individual NC sets and their sequence control the coordinated working movements of the devices and tools of the spring winding machine during the subsequent manufacturing process.

The feed device produces a wire feed at a defined feed rate. The wire is formed on the tools of the forming device to form a helical spring which develops ever further. The front spring end section which is produced first is in this case moved ever further away from the forming tools and, after passing through the spring guide device 210, finally enters the field of view 262 of the second camera 260. A feed interruption is programmed in the NC control program at a fixed predetermined point a number of turns before the end of manufacture, such that, for example, the feed is stopped one to five turns before the end of manufacture. This program time is chosen such that the free end section 220 of the spring on the side of the turn facing the second camera is located as far as possible in the central area between the high points and the low points of the turns. The spring end then appears as a more or less curved step in the projection of the image display. An image recording is then triggered by a trigger signal in the NC program at a measurement time, and is used as the basis for evaluation by the image processing.

The trigger signal need not come from the control program. For example, the drive unit for the wire feed may contain a position transmitter which produces a trigger signal at the correct position, at a desired point in the wire feed.

The position of the spring end formed by the end surface 222 of the wire is determined from the image or from the image data representing the image. In the example, an image processing measurement tool which operates in the form of a caliper gage is used for this purpose. In this case, a virtual upper limiter 272 is applied in the form of a tangent which runs more or less parallel to the spring axis 118 to the contour of the high point 224, and a lower limiter 274 is applied parallel to the upper limiter in the form of a tangent to the contour of the spring end. The vertical distance Y, which is represented by the double-headed arrow, between the limiters, is then stored as the measured value.

This measured value Y, which is determined in the side projection, (distance measured value) correlates directly with the angle position at the spring end at the measurement time, that is to say with the angle which the spring end includes with a reference direction, when considered in the axial direction of the spring, with this reference direction running vertically (on the plane of the drawing in FIG. 3), by way of example. A remaining distance is calculated on the basis of this measurement of the spring end through which the wire still has to be fed with the aid of the feed device for the spring end to be in the correct angle position with respect to the other spring end, which is produced at the opposite end with the aid of the cutting device at a later reference time. This calculated remaining distance is then transferred to the wire feed control system and is used as the basis for the rest of the feed process.

Depending on the spring type, the reference time may correspond to the end of manufacture or to an intermediate time which occurs before the end of manufacture.

In the example of a spring with contact sections at both ends, an intermediate time is reached at the end of the remaining distance, which is followed by a fixed programmed final part of the manufacture in which the opposite contact section is produced with a decreasing pitch, until the end of manufacture is reached. If the spring has an open end (constant pitch up to the spring end) at the opposite end, then the remaining distance is preferably calculated such that the end of the process of manufacturing the spring is reached at the end of the remaining distance.

An example of the evaluation of the measured value Y of the distance measurement which may be used will be explained with reference to FIGS. 6 and 7. FIG. 6 schematically illustrates an axial view of the free spring end section of a helical spring in which the turns which are located one behind the other in the axial direction appear as a single ring. This spring is recorded from the left with the aid of the second camera 260. The end surface 222 of the spring is shown in two different angle positions which will be explained later. As a result of the manufacturing process, the end surface of the spring is not at right angles to the center line of the wire, but is inclined with respect to it. The wire length measured along the wire is represented by the external arc length of the wire turn, that is to say by the arc length radially on the outside of the turns.

The calculation of the remaining distance starts from a fictitious remaining distance which corresponds to that remaining distance between the fictitious end position 222-1 of the spring end and the desired nominal position of the spring end at the reference time. The nominal angle position may, for example, be at a remaining distance of 60 mm (corresponding to an arc length which can be determined therefrom) from this fictitious position of the spring end. To determine the remaining distance which actually still needs to be fed, the evaluation process now searches for that arc length b which corresponds to the angular interval between the actually measured position of the spring end 222 and the fictitious position 222-1 of the spring end. This arc length b corresponds to a specific wire length. As can be seen directly from FIG. 6, in the example of the spring end surface 222 which is positioned obliquely, the measured value Y does not directly correspond with the sought arc length b since the lower limiter for the distance measurement has probed that contour which is formed by the internal radius of the turn. A situation such as this results whenever the end surface 222 can be seen from the viewing direction of the camera.

To avoid such errors which adversely affect the measurement accuracy, the relative orientation of the spring end with respect to the observation direction is determined at the measurement time, and the value for the distance value Y is corrected as a function of the orientation. For this purpose, before starting the process of manufacturing a batch of springs, the operator uses a reference measurement to determine that angle position of the spring end at which the end surface of the wire is precisely parallel to the observation direction. This situation, which is annotated with the reference symbol 222′, is referred to as the angle neutral position and, in the case of the distance measurement from the view of the second camera, would correspond to a distance value X, which can be referred to as the distance measure for the angle neutral position. This distance measure X is specific to the spring geometry and the type of cut.

The decision to be made by the evaluation system as to whether a correction is or is not required for the measurement because of the oblique position of the spring end surface can be considerably simplified by determining the angle neutral position and the associated distance measure X for the angle neutral position. Whenever the distance measured value Y measured in the subsequent measurement is greater than the distance measure X for the angle neutral position, the corresponding limiter of the distance measurement tool probes the external radius of the spring turn thus allowing the external arc length to be determined without any correction from geometric relationships. In contrast, as in the example in FIG. 6, if the measured distance value Y is less than the distance measure X for the angle neutral position, then the end surface 222 can be seen in the field of view and the internal radius of the turn is probed. This means that, if the measured value Y is less than the distance measure X for the angle neutral position, a correction is carried out.

FIG. 7 shows one possible calculation scheme for determining the sought arc length b. The following parameters, which are also shown in FIG. 6, are used in this case: r_a: external radius of the spring; r_i: internal radius of the spring; α′: angle between the angle null direction and the internal radius of the spring at the angle neutral position; β′: angle between the angle null direction and the direction of the external radius of the spring at the angle neutral position. In this case, it should be noted that the angle difference (α′−β′) is a constant which is governed by the geometry of the spring and the orientation of the spring end surface 222. The angles α and β correspond to the corresponding angles relating to the internal radius and external radius, respectively, during the measurement of the distance measure Y. The formulae in FIG. 7 show the way in which the sought arc measure b is derived from measured variables.

If the arc measure b has now been determined in the described way, or in some other way, then the remaining distance which actually still has to be moved through is calculated by subtracting the arc measure determined by measurement, or the wire length associated with it, from the fictitious remaining distance associated with the fictitious end position 222-1. Once the remaining distance has been determined, then a corresponding NC set is produced in the control system, and the wire feed feeds the wire through the calculated remaining distance. The constant final section is then also moved through, as a result of which the end surface 222 of the finished spring is located with high precision in the area of the nominal position of the spring end.

The feed through the remaining distance is carried out in a creeping process, that is to say it is carried out at a reduced feed rate. The creeping process is also used for the feed in the subsequent constant final section, until the entire length of the spring has been produced. This situation is illustrated schematically in FIG. 3 by turns in the form of dashed lines and in an enlarged form in FIG. 5. The field of view 262 of the second camera is sufficiently great that the spring end section with the spring end is within the field of view both for the intermediate measurement as described above (to determine the distance measure Y) and in the final position with the complete spring. In the example shown in FIG. 5, the second camera is used to carry out a measurement of the overall length of the finished spring. A second measurement area 266 is generated for this purpose, which represents a second measurement tool by means of which the longitudinal distance, identified by the arrow Z, between a measurement point 270 on the end face of the spring and the left-hand edge of the measurement tool 266 can be determined. The edge of this measurement window is in this case used as a “fixed stop” for the measurement, that is to say as a reference element whose coordinates with respect to a machine coordinate system of the spring winding machine are known or can be determined. The overall length of the spring can be measured absolutely and precisely in this way on the basis of the distance value Z.

The determination of the spring end position as explained in conjunction with FIGS. 3 and 4 can be used to further control the manufacturing process. In this case, it should be noted that the wire feed, that is to say the feed device, in general operates very precisely and substantially without slip, as a result of which the wire length fed by the feed device corresponds to a good approximation to the wire length predetermined by the machine program. If the measurements of the spring end position now show a tendency for the spring end position (angle position of the spring end after completion of the winding process) to be systematically less than expected or greater than expected, then this can indicate that the spring diameter has a tendency to be smaller than intended or larger than intended, respectively since, for example, with a larger diameter and the same wire length, an angle position of the spring end can be expected which is less than the desired nominal angle position. The evaluation system has an evaluation algorithm which identifies such tendencies in the measured positions of the spring end and feeds this information back to the control system, thus allowing the control system to implement an appropriate diameter correction, by adjusting the position of the winding pins, for the manufacture of the next springs. The measurement of the spring end position therefore also indirectly provides a determination of the spring diameter, and a correction option based on this.

The above description is directed to representative examples. From the disclosure given, those skilled in the art will not only understand our methods, apparatus and their attendant advantages, but will also find apparent various changes and modifications to the structures and methods disclosed. It is sought, therefore, to cover all changes and modifications as fall within the spirit and scope of this disclosure, as defined by the appended claims, and equivalents thereof.

Claims

1. A method of producing helical springs by spring winding with a numerically controlled spring winding machine comprising:

feeding a wire controlled by an NC control program through a feed device to a forming device;

forming the wire into a helical spring in the forming device;

defining a measurement time which occurs in a final phase of an overall manufacturing time for the helical spring at a time period before the end of the overall manufacturing time;

measuring a position of a spring end formed by an end surface of the wire to determine an actual angle position of the spring end at the measurement time;

determining a remaining distance for the wire feed required to achieve a nominal angle position of the spring end, as intended for the helical spring, at a predefined reference time which occurs at a time after the measurement time; and

feeding the wire through the remaining distance.

2. The method according to claim 1, wherein the reference time corresponds to the end of the overall manufacturing time.

3. The method according to claim 2, wherein an opposite spring end is produced immediately after reaching the reference time by separating the helical spring which has been produced from the fed wire.

4. The method according to claim 1, wherein the reference time is an intermediate time which occurs at a time before the end of the overall manufacturing time, wherein, after passage through the remaining distance, a predefined final part of the manufacturing time passes to the end of the overall manufacturing time, and the helical spring which has been produced is then separated from the fed wire.

5. The method according to claim 1, wherein a camera with a two-dimensional field of view measures the position of the spring end, and the camera is arranged such that an end section of the helical spring with the spring end lies within a field of view at the measurement time.

6. The method according to claim 5, wherein the camera is arranged alongside a path of the helical spring such that an observation direction is aligned transversely to a longitudinal direction of the helical spring.

7. The method according to claim 6, wherein the actual angle position of the spring end is determined from data from the field of view by determining a distance value for a distance, which is measured transversely to a longitudinal axis of the helical spring, between a tangent to an external contour of a turn on a circumference of the helical spring and a projection of the spring end in the field of view.

8. The method according to one claim 1, wherein a relative orientation of the spring end is determined at the measurement time with respect to an observation direction, and the measured distance value is corrected as a function of the orientation.

9. The method according to claim 1, wherein the measurement time is selected as a function of geometric data of the helical spring such that, in a remaining time interval required to move through the remaining distance, at least one turn of the helical spring is produced.

10. The method according to claim 1, wherein a feed movement of the wire is interrupted to carry out measuring the position of the spring end.

11. The method according to claim 1, wherein at least one further measurement is carried out after the end of the overall manufacturing time and before cutting off the helical spring from the wire fed through the feed device.

12. The method according to claim 11, wherein an overall length of the finished helical spring is determined on the basis of the further measurement.

13. A spring winding machine that produces helical springs by spring winding under the control of an NC control program according to the method of claim 1 comprising:

a feed device; and

a forming device that receives wire from the feed device and comprises at least one winding tool which controls the diameter of the helical spring at a predeterminable position, and at least one pitch tool whose action on a helical spring being produced controls a local pitch of the helical spring.

14. The spring winding machine according to claim 13, further comprising a camera positioned at a distance from the forming device such that a free spring end section runs into a field of view of the camera in a final phase of production of the helical spring.

15. A computer program product stored on a computer-readable medium or in the form of a signal, wherein the computer program product results in the computer carrying out the method according to claim 1 when the computer program product is loaded in the memory of a computer and is run by a computer of a spring winding machine.