ULTRASONIC WELDING SYSTEM WITH DYNAMIC PRESSURE CONTROL
An ultrasonic welding system for securing a first work piece to a second work piece includes a welding assembly and a loading assembly disposed adjacent to the welding assembly. The welding assembly includes an ultrasonic controller, an ultrasonic transducer, and a welding tip. The ultrasonic transducer is configured to impart an ultrasonic vibration to the welding tip in response to an electrical signal received from the ultrasonic controller. The loading assembly is configured to generate a pressure load between the welding tip and the first work piece, and includes a first actuator and a second actuator. The first actuator is configured to apply a substantially constant load to the welding assembly, and the second actuator is configured to apply a dynamically variable load to the welding assembly.
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The present invention relates generally to an ultrasonic welding system with dynamic pressure control.
BACKGROUNDUltrasonic welding is the process of fusing two work pieces together using ultrasonic acoustic vibrations. Ultrasonic welding can be used for both hard and soft plastics, such as semicrystalline plastics, and metals. Typically, the materials are sandwiched between a welding tip, also referred to as a sonotrode or horn, and an anvil. The welding tip imparts the ultrasonic vibrations to the work pieces, which locally melts or transforms the work pieces around the point of contact. This local material transformation is a result of the work pieces absorbing the vibration energy. The joint may be formed by either by fusion or covalent bonds in the case of dissimilar metals as a result of the input energy which includes the frequency and amplitude of the vibrations, the surface properties of the joining materials, and the pressure applied at the intended joint.
SUMMARYAn ultrasonic welding system for securing a first work piece to a second work piece includes a welding assembly and a loading assembly disposed adjacent to the welding assembly. The welding assembly may include an ultrasonic controller, an ultrasonic transducer, and a welding tip. The ultrasonic transducer may be configured to impart an ultrasonic vibration to the welding tip in response to an electrical signal received from the ultrasonic controller. The loading assembly may then be configured to generate a pressure load between the welding tip and the first work piece, and includes a first actuator and a second actuator. The first actuator is configured to apply a substantially constant load to the welding assembly, and the second actuator is configured to apply a dynamically variable load to the welding assembly.
In one configuration, the first actuator may be a pneumatic actuator, and the second actuator may be a piezoelectric actuator, which may be, for example, disposed in a series arrangement with the welding assembly. The loading assembly may further include a pressure controller, and the piezoelectric actuator may be configured to apply the dynamically variable load to the welding assembly in response to an electrical signal provided by the pressure controller. The pressure controller may be configured to provide this electrical signal to the piezoelectric actuator in response to an indication of the real-time power of the electrical signal provided to the ultrasonic transducer. In an embodiment, the pressure controller may be configured to vary the electrical signal provided to the piezoelectric actuator such that the power of the electrical signal provided to the ultrasonic transducer tracks a pre-defined power curve.
The ultrasonic controller may be configured to vary the power of the electrical signal provided to the ultrasonic transducer such that the ultrasonic transducer generates an ultrasonic vibration having a substantially constant frequency. The ultrasonic vibration may have a frequency within the range of about 5 kHz to about 100 kHz. Likewise, the electrical signal provided by the pressure controller may be updated at a rate greater than twice the frequency of the ultrasonic vibration.
Additionally, a method for performing an ultrasonic welding operation with dynamic weld pressure control may include actuating a first actuator to translate a welding tip of an ultrasonic welding assembly into contact with a work piece, and imparting a pressure load between the welding tip and the work piece. A fixed frequency ultrasonic vibration may then be generated in the welding tip by providing an ultrasound transducer coupled to the welding tip with an electrical signal having a measurable power. The real-time power of the electrical signal may be monitored, and a second actuator may be actuated in response to the monitored real-time power of the electrical signal. The actuation of the second actuator may be configured to vary the pressure load between the welding tip and the work piece.
The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.
Referring to the drawings, wherein like reference numerals are used to identify like or identical components in the various views,
During a welding procedure, the welding tip 16 may apply a transverse pressure load 18 or normal force to the first work piece 12. In one configuration, the pressure load 18 may compress, or clamp the first work piece 12 against the second work piece 14. In other configurations, secondary clamping devices may be used to hold the work pieces 12, 14 in a temporarily rigid arrangement, relative to each other, while the weld is formed. An anvil 20 may be disposed on an opposite side of the work piece arrangement 12, 14 from the welding tip 16, and may restrain the applied pressure load 18 from bending, or otherwise deforming the work pieces 12, 14. Said another way, the work pieces 12, 14 may be sandwiched between the welding tip 16 and an anvil 20.
An ultrasound transducer 24 may impart a periodic, vibratory motion 26 to the welding tip 16 in a direction that is generally co-planar with the surface 28 of the first work piece 12. More particularly, the vibratory motion 26 may be a generally linear oscillation along the surface 28. The vibratory motion 26 may have a substantially constant periodic frequency that falls within the range of about 5 kHz to about 100 kHz. For example, in a particular example where the work pieces are metal, the frequency of the vibratory motion 26 may be about 20 kHz.
The ultrasound transducer 24 may include a piezoelectric material that generates the mechanical motion 26 in response to an electrical signal 30. In an embodiment, a mechanical amplifier 32 may be positioned in a series arrangement between the transducer 24 and the welding tip 16. The mechanical amplifier 32 may be specially configured to resonate at the set frequency of the ultrasound transducer 24 (or vice versa). By tuning the amplifier 32 to the frequency of the transducer 24, small motions generated by the transducer 24 may be enhanced in magnitude by the amplifier 32, which may be then transferred through, for example, a shank 34 to the welding tip 16.
While the welding tip 16 provided in
As generally illustrated in
In addition to dynamic changes in the frictional forces 42 due to the variable resultant contact pressure loading (i.e., the applied pressure load 18 minus any dynamic lifting forces 44), the frictional force 42 may vary due to changes in the material properties of the first work piece 12. For example, as the ultrasonically applied friction forces 42 locally heat the work piece 12, it may soften, which may alter the ability of the tip 16 to transfer ultrasonic energy into the work piece 12.
Referring again to
The ultrasonic controller 50 may be embodied as one or multiple digital computers or data processing devices, each having one or more microprocessors or central processing units (CPU), read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, input/output (I/O) circuitry, power electronics/transformers, and/or signal conditioning and buffering electronics. The individual control routines/systems resident in the ultrasonic controller 50 or readily accessible thereby may be stored in ROM or other suitable tangible memory location and/or memory device, and automatically executed by associated hardware components of the controller 50 to provide the respective control functionality.
The ultrasonic controller 50, ultrasonic transducer 24, mechanical amplifier 32, shank 34 and welding tip 16 may generally comprise the ultrasonic welding assembly 60. Adjacent the ultrasonic welding assembly 60 may be a loading assembly 62, which may be configured to generate and control the application of the transverse pressure load 18 between the welding tip 16 and the first work piece 12. As will be discussed, the loading assembly 62 may generally be configured to translate the welding tip 16 until a threshold contact is established between the tip 16 and the first work piece 12. It may then dynamically refine the applied pressure load 18 to account for variable lifting forces 44 and/or changing material conditions.
The loading assembly 62 may include a first actuator 64 and a second actuator 66 disposed in a series arrangement with the welding assembly 60. In one embodiment, the first actuator 64 may be configured for low frequency, high amplitude movement. Comparatively, the second actuator 66 may be configured for high frequency, low amplitude movement. In this configuration, the first actuator 64 may be used to move the welding tip 16 into contact with the first work piece 12 and to generate a steady state pressure load 18. The second actuator 66 may then be used to counteract dynamic/transient pressure load changes, which may be attributable to the ultrasonic vibrations 26, yet may be too quick for the first actuator 64 to compensate for. Said another way, the first actuator 64 may be configured for steady state translations of the welding assembly 60, while the second actuator 66 may be configured for high-speed, dynamic adjustments.
As illustrated in
The piezoelectric actuator 67 may be disposed between the ram 72 and the welding assembly 60, and may be configured to expand and contract in a dimension 80 transverse to the work piece 12 in response to an electrical actuation signal 82 provided by the pressure controller 68. Piezoelectric actuators, such as the one illustrated, are generally capable of producing high-force, highly precise actuation responses, though only over short stroke lengths (e.g., less than 100 micrometers). Additionally, because the response time of piezoelectric actuators is extremely fast (e.g., capable of over 10 MHZ actuation), they may be suitable to dynamically adjust the applied pressure load 18 through the welding tip 16 multiple times within one ultrasonic cycle (e.g., the update speed of the pressure applied by the piezoelectric actuator 67 may be greater than twice the ultrasonic vibration frequency).
The pressure controller 68 may dynamically modulate the applied pressure load 18 by controlling the actuation of the piezoelectric actuator 67 via the electrical actuation signal 82. In one embodiment, the pressure controller 68 may modulate the applied pressure load 18 in response to an indication of the power 90 of the electrical signal 30 provided to the ultrasonic transducer 24, which may be provided to the pressure controller 68 by the ultrasound controller 50. More specifically, the pressure controller 68 may modulate the applied pressure load 18, via the piezoelectric actuator 67 such that the power of the electrical signal 30 provided to the ultrasonic transducer 24 follows a pre-defined power trajectory 92, such as generally represented in
While the power of the electrical signal 30 provided to the ultrasonic transducer 24 is directly related to the power injected into the weld, as described above, it is separately controlled by the ultrasonic controller 50 to maintain a constant generated frequency. By adjusting the applied pressure load 18, however, the pressure controller 68 may effectively modulate the amount of power transferred into the work piece 12, thus indirectly affecting the power provided to the ultrasound transducer 24. This dynamic adjustment may be performed in a closed-loop manner by comparing the indication 90 of the current power of the signal 30 (provided by the ultrasonic controller) to the pre-defined trajectory 92. While conventional PID-type control loops may be used to dynamically control the response of the piezoelectric actuator 67, other more advanced predictive control methods may similarly be used to account for the high frequency dynamics.
The pressure controller 68 may be embodied as one or multiple digital computers or data processing devices, each having one or more microprocessors or central processing units (CPU), read only memory (ROM), random access memory (RAM), electrically-erasable programmable read only memory (EEPROM), a high-speed clock, analog-to-digital (A/D) circuitry, digital-to-analog (D/A) circuitry, input/output (I/O) circuitry, power electronics/transformers, and/or signal conditioning and buffering electronics. The individual control routines/systems resident in the pressure controller 68 or readily accessible thereby may be stored in ROM or other suitable tangible memory location and/or memory device, and automatically executed by associated hardware components of the controller 68 to provide the respective control functionality.
Referring to
In other configurations, rather than tracking a pre-defined power curve/trajectory as shown with
The dynamic control of the piezoelectric actuator 67 may further be configured to reduce the applied pressure load 18 in the event a fault or error condition is detected. For example, if the actual power 100 is not responding as expected, the pressure controller 68 may direct the piezoelectric actuator 67 to reduce the applied pressure load 18 to avoid damaging the work piece.
While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. It should be understood that the first actuator 64 can be any actuator capable of longer stroke lengths, such as pneumatic or hydraulic actuators, lead or ball screws, solenoids, etc. . . . Likewise, the second actuator 66 may be any actuator capable of a high-frequency response (i.e. more than twice the frequency of the ultrasonic vibration 26). It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not as limiting.
Claims
1. An ultrasonic welding system for securing a first work piece to a second work piece, the system comprising:
- a welding assembly including an ultrasonic controller, an ultrasonic transducer, and a welding tip; the ultrasonic transducer configured to impart an ultrasonic vibration to the welding tip in response to an electrical signal received from the ultrasonic controller; and
- a loading assembly disposed adjacent to the welding assembly and configured to generate a pressure load between the welding tip and the first work piece, the loading assembly including a first actuator and a second actuator;
- wherein the first actuator is configured to apply a substantially constant load to the welding assembly; and
- wherein the second actuator is configured to apply a dynamically variable load to the welding assembly.
2. The ultrasonic welding system of claim 1, wherein the loading assembly further includes a pressure controller; and
- wherein the second actuator is configured to apply the dynamically variable load to the welding assembly in response to an electrical signal provided by the pressure controller.
3. The ultrasonic welding system of claim 2, wherein the pressure controller is configured to provide the electrical signal to the second actuator in response to an indication of the real-time power of the electrical signal provided to the ultrasonic transducer.
4. The ultrasonic welding system of claim 3, wherein the pressure controller is configured to vary the electrical signal provided to the second actuator such that the power of the electrical signal provided to the ultrasonic transducer tracks a pre-defined power curve.
5. The ultrasonic welding system of claim 4, wherein the ultrasonic controller is configured to vary the power of the electrical signal provided to the ultrasonic transducer such that the ultrasonic transducer generates an ultrasonic vibration having a substantially constant frequency.
6. The ultrasonic welding system of claim 2, wherein the ultrasonic vibration has a frequency within the range of about 5 kHz to about 100 kHz; and wherein the electrical signal provided by the pressure controller is updated at a rate greater than twice the frequency of the ultrasonic vibration.
7. The ultrasonic welding system of claim 1, wherein the first actuator and the second actuator are disposed in a series arrangement with the welding assembly.
8. The ultrasonic welding system of claim 1, wherein the first actuator is a pneumatic actuator, and wherein the second actuator is a piezoelectric actuator.
9. A method for performing an ultrasonic welding operation with dynamic weld pressure control comprising:
- translating a welding tip of an ultrasonic welding assembly into contact with a work piece using a first actuator, the translating further configured to impart a pressure load between the welding tip and the work piece;
- generating a fixed frequency ultrasonic vibration in the welding tip, the generating including providing an ultrasound transducer coupled to the welding tip with an electrical signal having a measurable power;
- monitoring the real-time power of the electrical signal; and
- providing an electrical actuation signal to a second actuator in response to the monitored real-time power of the electrical signal, the electrical actuation signal configured to cause the second actuator to vary the pressure load between the welding tip and the work piece.
10. The method of claim 9, wherein the magnitude of the electrical actuation signal is varied to cause the monitored real-time power of the electrical signal to track a pre-defined curve.
11. The method of claim 9, wherein the fixed frequency ultrasonic vibration has a frequency within the range of about 5 kHz to about 100 kHz.
12. The method of claim 11, wherein the electrical actuation signal is updated at a rate greater than twice the frequency of the ultrasonic vibration
13. The method of claim 12, wherein the response time of the second actuator is greater than the response time of the first actuator.
14. The method of claim 9, further comprising amplifying ultrasonic vibrations using a mechanical amplifier having a resonant frequency.
15. The method of claim 9, further comprising providing the first actuator and the second actuator in a series arrangement with the ultrasonic welding assembly.
16. The method of claim 9, wherein the first actuator is a pneumatic actuator, and wherein the second actuator is a piezoelectric actuator.
17. An ultrasonic welding system for securing a first work piece to a second work piece, the system comprising:
- a welding assembly including an ultrasonic controller, an ultrasonic transducer, and a welding tip; the ultrasonic transducer configured to impart an ultrasonic vibration to the welding tip in response to an electrical signal provided by the ultrasonic controller; and
- a loading assembly disposed adjacent to the welding assembly and configured to generate a pressure load between the welding tip and the first work piece, the loading assembly including a pneumatic actuator and a piezoelectric actuator, and a pressure controller in electrical communication with the piezoelectric actuator; and
- wherein the pneumatic actuator is configured to apply a substantially constant load to the welding assembly; and
- wherein the piezoelectric actuator is configured to apply a dynamically variable load to the welding assembly in response to an electrical actuation signal provided by the pressure controller.
18. The ultrasonic welding system of claim 17, wherein the electrical signal provided by the ultrasonic controller has a measurable power; and
- wherein the pressure controller is configured to provide the electrical actuation signal to the second actuator in response to an indication of the power of the electrical signal provided by the ultrasonic controller.
19. The ultrasonic welding system of claim 18, wherein the ultrasonic vibration has a frequency within the range of about 5 kHz to about 100 kHz; and wherein the electrical actuation signal provided by the pressure controller is updated at a rate greater than twice the frequency of the ultrasonic vibration.
20. The ultrasonic welding system of claim 19, wherein the electrical actuation signal provided by the pressure controller is varied to minimize the deviation between indication of the power of the electrical signal provided by the ultrasonic controller and a pre-defined power curve.
Type: Application
Filed: Nov 4, 2011
Publication Date: May 9, 2013
Applicant: GM GLOBAL TECHNOLOGY OPERATIONS LLC (Detroit, MI)
Inventors: John Patrick Spicer (Plymouth, MI), Benjamin R. Christian (Novi, MI), Jeffrey A. Abell (Rochester Hills, MI)
Application Number: 13/289,530
International Classification: B32B 37/06 (20060101); B23K 20/10 (20060101); B29C 65/08 (20060101); B23K 37/00 (20060101);