Abstract: This invention relates to methods to control the resistance spotwelding process using an electric servomotor actuator to move the welding electrodes to the work and apply force to them. Measurements of actuator position, servomotor drive voltage, servomotor drive current, voltage across the welding electrodes, welding transformer primary current, welding transformer secondary current and power factor in the primary circuit of the welding transformer are used separately and in combination to determine various conditions such as identify defects in the welding machine, the electric cabling, the welding process and in the weld itself. Depending upon the defect found, the welding parameters are changed to overcome the defect, and/or the need for an additional weld is indicated and/or an error indication is generated.

Abstract: This invention relates to methods to control the resistance spotwelding process using an electric servomotor actuator to move the welding electrodes to the work and apply force to them. Measurements of actuator position, servomotor drive voltage, servomotor drive current, voltage across the welding electrodes, welding transformer primary current, welding transformer secondary current and power factor in the primary circuit of the welding transformer are used separately and in combination to determine various conditions such as identify defects in the welding machine, the electric cabling, the welding process and in the weld itself. Depending upon the defect found, the welding parameters are changed to overcome the defect, and/or the need for an additional weld is indicated and/or an error indication is generated.

Abstract: A calibration algorithm is provided for calibrating a machine vision system including a color camera, a framegrabber and an illumination source wherein subsequently acquired images are processed on a pixel-by-pixel basis. After framegrabber offsets are measured to obtain initial or offset calibration data, the camera is pointed at a target monotone patch of known reflectance such as pure white and the camera outputs for red, green and blue are determined while observing the monotone patch to obtain spatial calibration data. The gain for each of the output channels of the color camera is automatically determined from the initial calibration data. Applying the three gain factors to a subsequent image on the pixel-by-pixel basis allows one to end up with a color-corrected image without incurring any time performance penalty. At any time during an inspection process, a small area of white reflectance can be observed.

Abstract: A method is provided for calibrating a tilt inspection system and a reference disk assembly for use therein wherein a mirror disk of the assembly is attached to a rotatable member of the system by a beveled washer so that the mirror disk rotates at a predetermined tilt angle with respect to an axis of rotation of the rotatable member. As the reference disk assembly is rotated by the tilt inspection system at a relatively slow and constant angular velocity, a beam of light is reflected off the mirror disk to a position sensitive detector (i.e., PSD) and subscribes a circle on the face of the PSD. The tilt inspection system samples the channels from the PSD throughout one revolution of the mirror disk. Calibration or reference data is calculated in the form of tilt transformations.

Abstract: A method and system are described for use at a machine vision station to correctly identify errors within a sample image of an object by means of a probability image where a value of each pixel of the probability image is a probability. The probability image is created from a mean template image and a standard deviation image, both of which are created from a plurality of reference images of the object. The probability image is processed to detect the errors in the sample image independent of the values of the pixels which make up the sample image. Two different techniques are described for creating the probability image utilizing mean template, sample and standard deviation pixel values.

Abstract: A method and system are provided for tuning a drive to its coupled stepper motor to minimize motor resonance wherein an electronic accelerometer is mounted in a coupler such as a slip clutch to sense angular accelerative forces of an output shaft of the motor. The slip clutch is slid over the output shaft to permit rapid coupling to and decoupling from the output shaft. The slip clutch is preferably spring-loaded to allow for a relatively constant grip to the output shaft over a normal range of shaft tolerances. A signal generated by the accelerometer is processed to obtain an output signal which is displayed to indicate variations in the angular accelerative forces. The drive is then adjusted to reduce the motor resonance based on the displayed variations.

Abstract: A method and system are provided for interactively developing a graphical, control-flow structure and associated application software for use in a machine vision system using a computer system without the need for a user to write any code. Preferably, the method and system "marry" the ActiveX control standard and the Grafcet/IEC 1131 standard. The structure includes a control sequence having a plurality of steps or nodes, transitions, and links or flow lines which interconnect the nodes and transitions. Hardware operating parameters are stored which correspond to possible hardware for use in the machine vision system. The hardware operating parameters define a set of standard controls having properties. Commands are received from the user of the computer system to select a first control program corresponding to a desired component of a user interface, desired hardware operating parameters corresponding to desired hardware and second control programs corresponding to desired machine vision algorithms.

Abstract: A pair of calibration algorithms are provided for calibrating a color camera in a machine vision system. The first and most general form of the calibration algorithm requires that a calibration target be shown to a well adjusted machine vision system. The calibration target contains samples of red, green and blue. A gray level histogram is taken of each of the resulting red, green and blue images and is used to generate corresponding standard cumulative probability functions. The standard cumulative probability functions, together with a copy of the calibration target, is provided to a machine vision system having its own color camera which requires calibration. The same above-noted steps are repeated for this system and the resulting cumulative probability functions are compared to the corresponding standard cumulative probability functions to obtain gains for the red, green and blue channels of the camera to be calibrated .

Abstract: A method and system are provided for measuring a two-dimensional deflection angle of a beam of light reflected from a disk having unknown radial and tangential tilt components by first generating reference data relating to known tilt of a reference disk and then processing the reference data with electrical signals from a two-dimensional photodetector to obtain values related to the deflection angle and the unknown radial and tangential tilt components. The photodetector is preferably a semiconductor photodiode having an active area which measures position of radiant energy in a spot of light focused in a detector plane by a focusing lens. A signal processor including a computer system programmed in accordance with a software algorithm compensates for interaction between X and Y axes of the active area of the photodiode to compensate for alignment errors or tolerances, not only up, down, left and right, but also for rotational errors as well.

Abstract: A signal integrator stabilization circuit comprises an operational amplifier functioning as a comparator. The circuit further comprises an attenuator in the amplifier's feedback, thereby generating a feedback signal which is sampled to produce a sampling signal. The integrator is driven with a preselected ratio of the feedback signal and the sampling signal to produce a stabilized output signal approaching a zero value which has a good DC stability without compromising the ability to accurately integrate high frequency signals.

Abstract: Color balance of a sample image is compared with a previously learned template image utilizing an appropriately programmed machine vision system including a color camera at a vision station. The sample image, preferably captured from a web scanner attached directly to an offset printing machine, is compared with a previously generated "known good" template image. This comparison process produces four correction factors which are the ratios between the amount of each of four colored inks in the template image to that in the sample image. The four colored inks may be cyan, magenta, yellow, and black inks but inks of other colors could also be used. These correction factors can either be presented to an operator to manually adjust the machine or else used in an automatic feedback loop of a controller of the machine, thereby maintaining consistent image quality.

Abstract: A method and system are provided for reliably detecting localized birefringence defects of an object such as an optical media substrate in a dynamic local birefringence field created during cooling of the optical media substrate at an inspection station. A birefringence digital filter filters out high frequency defect data while eliminating background birefringence data in a digital image created by a camera adapted to respond to the birefringence of the optical media substrate under control of a computer. Resulting filtered high frequency defect data is then processed to determine the localized birefringence defects in real-time. In one embodiment, the birefringence digital filter includes an addressable storage device such as a PROM which stores a lookup table which is able to produce filtered data in real-time at a data rate in excess of 8 million pixels per second.

Abstract: A method and system for controlling the output current of large, low-voltage, DC power supply which includes at least one transformer primary by controllably switching an AC power line voltage to the primary as a function of actual and desired output currents. SCRs are used to switch, using phase control, the AC primary voltage to the transformer(s) of the power supply in order to control the output current. Given the incoming power line voltage, the current value from the previous power line cycle and the desired current for the present cycle, the function is used to find the SCR firing angle to attain the desired output current in the present power line cycle. Actual measurements of output current and power line voltage are used to modify the function to reflect changes in power line voltage and/or circuit impedance to obtain a modified function.

Abstract: The intensity of each lamp which illuminates an object at an inspection station is controlled by controlling driving voltage applied to a power supply which supplies electrical power to the lamp. A phototransistor is used to sense the intensity of the lamp through an optical fiber. The sensor is followed by a digitally-controlled, variable gain circuit whose output is fed to an A-D converter. A microprocessor analyzes the digital signal from the A-D converter and corrects the driving voltage to the power supply to keep the intensity output of the lamp constant, as seen by a camera of a machine vision system. In this way, feedback corrects for a degraded lamp output due to aging. Preferably, the control of the level of lamp intensity can be changed from a remote system console of the machine vision system to reduce the need for access to internal parts, thereby reducing the probability that human error may cause a malfunction.

Abstract: A method and system are provided for automatically and quantitatively measuring color difference between a color distribution of an object and a reference color image using "color distance" in a color system. A template representing the reference color image is stored in a memory of a machine vision system. The machine vision system generates a sample color image of the object and processes the template together with the sample color image to obtain a total color distance. Color distance may be measured either in a Euclidean or "City Block" fashion. Preferably, a look-up table stores the template. The color system may be either intensity dependent or independent. The total color distance can either be presented or displayed to an operator of the machine vision system or else can be used in an automatic feedback loop of a controller of a machine or process.

Abstract: A method and system are provided for quickly developing application software for use in a machine vision system using a computer system. Hardware operating parameters are stored which correspond to possible hardware for use in the machine vision system. The hardware operating parameters define a set of custom controls having properties. Commands and a set of instructions are received from a user of the computer system to select a first custom control program corresponding to a desired component, desired hardware operating parameters corresponding to desired hardware and a second custom control program corresponding to a desired machine vision algorithm. The first custom control program is linked with the desired hardware operating parameters to the second custom control program to form the application software.

Abstract: Spectral transmittance of a dye coating for optical data is determined off-line. Light source wavelength is then matched to the wavelengths at which the dye has the least transmission (i.e. maximum absorbance). The method and system of the present invention are provided for detecting local and global defects in the coating wherein the inspection is done at the maximum absorbance wavelengths to produce a maximum change in a transmitted light signal for a given change in physical thickness of the dye coating. Relative change in thickness is determined based on the change in the transmitted light signal through the dye coating. In order to complete detection and measurement of the transmittance changes, a pair of electronic signals are split from a camera signal wherein one of the electronic signals is filtered by a FIR filter to identify local changes in dye thickness against a globally varying background.

Abstract: A non-contact, non-destructive measurement method and system for the edge of parts such as the cutting edge or "hone" of tools wherein the shape and dimensions of the hone are measured with high accuracy (i.e., within 5 microns) and repeatability. Given a tool that is mechanically fixtured under the system and a set of user-defined parameters, the measurement system automatically detects a measurement area for different orientations of the tool. Manual selection of the measurement area is also possible. The system then uses a combination of Moire interferometry and image analysis algorithms to compute the shape and dimension of the hone for both radius and waterfall types.

Abstract: First and second linearly polarized beams of light are incident on a magneto-optical disc at a common point. Both beams have equal or nearly equal intensity. Upon specular reflection from the disc, the first and second reflected beams travel through analyzers which are the same linear polarizers which originally polarized the second and first beams, respectively. The polarizers have an orientation such that the polarization angle between the first beam and the first polarizer is the same as the polarization angle between the second beam and the second polarizer. Consequently, the difference between the intensities of the two analyzed beams is proportional to Kerr rotation and independent of the direction of the stress axes of the magneto-optical disc substrate, and only mildly dependent on the magnitude of the retardation of the substrate.

Abstract: A method and system are provided including an optical head which moves relative to an object at a vision station to scan a projected pattern of imagable electromagnetic radiation across the surface of an object to be inspected at a relatively constant linear rate to generate an imagable electromagnetic radiation signal. In one embodiment, the electromagnetic radiation is light to develop dimensional information associated with the object. The optical head includes at least one projector which projects a grid of lines and an imaging subsystem which includes a trilinear array camera as a detector. The camera and the at least one projector are maintained in fixed relation to each other. Three linear detector elements of the array camera extend in a direction parallel with the grid of lines. The geometry of the optical head is arranged in such a way that each linear detector element picks up a different phase in the grid pattern.