PIEZOELECTRIC POLYMER SENSOR DEVICE

Abstract

A sensor device includes at least one piezoelectric polymer film supported on a plate that is positioned relative to a machine such that a force used during a manufacturing process involving the machine is incident on the plate. The piezoelectric polymer film provides an electrical output indicative of the incident force. In a disclosed example, a single piezoelectric polymer film extends across a substantial portion of a surface area of the plate. In another disclosed example, a plurality of piezoelectric polymer film sensor elements area are arranged symmetrically about a location where the incident force is expected to be most prominent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an example machine incorporating an example sensor device designed according to an embodiment of this invention.

FIG. 2 schematically illustrates one example arrangement.

FIG. 3 illustrates the arrangement of FIG. 2 from another perspective.

FIG. 4 schematically illustrates another example arrangement.

FIG. 5 illustrates the arrangement of FIG. 4 from another perspective.

FIG. 6 schematically illustrates another example sensor device arrangement.

DETAILED DESCRIPTION

Disclosed example embodiments of a sensor device use piezoelectric polymer film sensor technology supported on a plate that experiences a force applied by an associated part forming machine. The disclosed examples ensure that the compression forces that occur during the part forming (e.g., wire crimping) are in series with the sensor device, minimizing any shunting effect and eliminating edge loading condition characteristics associated with traditional sensing arrangements. Additionally, the disclosed examples provide for boosting an output signal level per unit of measured force.

FIG. 1 schematically shows an example machine 20 that is used for a manufacturing or part forming process. The machine 20 includes a machine frame 22. A ram 24 moves relative to the frame 22 for generating a force used for a part forming process. Applicator tooling 26 operates in a known manner to perform a desired part formation process. A sensor device 30 is associated with the machine 20 for providing an indication of the forces occurring during a part forming process so that the quality of at least one of the resulting part, the process used to make the part or the applicator tooling can be determined.

Referring to FIGS. 2 and 3, one example sensor device 30 is shown associated with selected portions of a machine that is used for a wire crimping process. Crimping wire terminals is a known process that is used for many manufacturing or assembly processes for various purposes. One example purpose for wire crimping processes are for preparing wire harnesses for use in an automobile.

The example sensor device 30 includes a plate 32 that supports at least one piezoelectric polymer film 34. One example piezoelectric polymer film comprises polyvinylidene difluoride (PVDF). In the example of FIGS. 2 and 3, two separate piezoelectric polymer film elements 34A and 34B are supported on the plate 32. In the illustrated example, the plate 32 comprises a first plate portion 36 and a second plate portion 38.

The piezoelectric polymer film elements 34A and 34B are sandwiched between the plate portions 36 and 38 in this example. In examples where each of the plate portions 36 and 38 are electrically conductive, the polymer film 34 is used to isolate them from each other to avoid shorting out the positive and negative sides of the polymer film. In some examples, the piezoelectric polymer film has an electrically negative side and an oppositely facing, electrically positive side. Isolating metal plate portions avoids the plates shorting out the film, which would otherwise happen if the metal plate portions contact each other and contact the positive and negative sides of the film, respectively. In one example, two piezoelectric polymer films are placed adjacent each other with the positive sides of the films facing each other. In such an example, the metal plate portions only contact the outwardly facing negative sides of the films so that there is no concern with shorting out the films.

The piezoelectric polymer film elements 34A and 34B provide an electrical output that is indicative of a force incident on the plate 32 during a part forming process. As can be appreciated from FIG. 2, the example plate 32 is positioned between an applicator tool base 40 and a plate of the machine frame 22. Forces involved in the operation of crimping portions 42 and 44 of the applicator tooling 26 while establishing a wire crimp schematically shown at 46 are incident on the plate 32. The piezoelectric polymer film elements 34A and 34B provide an electrical output that is indicative of such forces.

In one example, the outputs from the piezoelectric polymer film elements 34A and 34B are summed using suitable electronics or software configured for such signal processing to provide a higher output value per unit of detected force compared to that from either element, alone. The summing also avoids any cancellation effects if there is an offset or misaligned incident force.

As can best be appreciated from FIG. 3, the forces associated with the part forming process will be concentrated at a location 50. In the illustrated example, this location is aligned with a scrap shoot 52, which comprises an opening through the plate 32 and corresponding portion of the frame 22. The piezoelectric polymer film elements 34A and 34B are arranged symmetrically about the location 50 where the part forming force is expected to be most prominent (e.g., concentrated or centered). The symmetric arrangement of the piezoelectric polymer film elements 34A and 34B eliminates any shunting of the forces detected by the sensor device 30. Such an arrangement improves sensitivity, the signal-to-noise ratio and repeatability.

The illustrated arrangement also eliminates any need for a mounting bolt as was required with previous crimp force monitors that relied on sensor rings. Such a mounting bolt has the drawback that it can shunt a portion of an applied force in a traditional sensor, which introduces inaccuracies. Using a piezoelectric polymer film as schematically shown, therefore, provides an improved sensor device.

With at least one piezoelectric polymer film sensing element between the plate portions 36 and 38, the complete surface of the plate 32 becomes a sensing surface. The surface of the plate 32 is essentially a sensing table or platform. This arrangement ensures that compression forces that occur during a part forming process are completely in series with the sensing elements. This minimizes any shunting effect and eliminates edge loading conditions.

Traditional single axis crystal or ceramic sensors cannot correct for directionality of loading because they are designed to measure forces applied in an axial direction. If one side of a force ring is loaded higher than the other side (e.g., in the case of edge loading with a bending moment), the resulting generated charge distributes evenly about the top and bottom electrodes with a cancellation effect. The overall effect is that a single force ring sensor offset to one side cannot distinguish finer process variation (e.g., slight rocking of an applicator tool) from actual failure when a small gauge terminal is being used in the forming process. The illustrated example of FIGS. 2 and 3, on the other hand, is not affected by edge loading and there is no such output cancellation condition. Accordingly, the illustrated example provides improved measurement accuracy and repeatability.

Additionally, it boosts the output signal per unit of input force. The inherent properties of a piezoelectric polymer such as PVDF provide improved signal-to-noise ratios when compared to conventional piezoelectric crystals (e.g., quartz) and piezoelectric ceramics (e.g., PZT). In a simple compressive mode, a piezoelectric material voltage output in response to an applied force is governed by the piezo stress constant (g₃₁). PZT, for example, typically has a g₃₁=10×10⁻³ Vm/N while a piezoelectric polymer has a g₃₁=216×10⁻³ Vm/N. Accordingly, a piezoelectric polymer film arrangement as schematically shown in FIGS. 2 and 3 can generate more than 20 times the voltage signal for a given level of load compared to conventional piezoelectric crystals or ceramics.

The example arrangement provides improved robustness and reliability by design because the piezoelectric polymer film sensor elements 34A and 34B are mechanically integrated into the plate 32. In the illustrated example, the sensor film elements are sealed between the plate portions 36 and 38. In one sense, the piezoelectric polymer film sensor elements 34A and 34B can be considered a gasket sandwiched between the first plate portion 36 and the second plate portion 38. This example eliminates any requirement for maintaining an air gap of the kind that previously has been required to isolate a force ring.

As shown in FIG. 3, the plate 32 supports a signal processor 60, which in this example comprises electronics, that process signals provided by the piezoelectric polymer film sensing elements 34A and 34B. Electrical connections between the elements 34A and 34B and the electronics 60 are schematically shown at 62. Including microcontroller technology on the plate 32 allows for sensor power control and signal conditioning at the location of the sensing elements. Additionally, high speed data collection at that location allows for providing a digital output from the sensor device 30 that is available directly from the location of the plate 32.

Such an arrangement provides several advantages. First, the power for the sensor device is regulated at the sensor. High speed data capture local to the sensing elements eliminates the effect of noise introduced by any cables between the plate 32 and another data processing element. The piezoelectric polymer sensor output is converted from analog to digital format local to the sensing elements and exported to another device such as a computer in a convenient manner, for example, using an industry standard compliant communication interface. Such an arrangement allows for providing signature analysis software algorithms in such a computer and does not require it to be part of crimp force monitor hardware. One advantage to such an arrangement is that the signature analysis software may be on one machine that receives information from a variety of sensor devices rather than requiring such software on each of the sensor devices.

In one example, the electronics 60 include a microprocessor that is programmed to analyze the signal signature from the piezoelectric polymer film sensing element or elements and to provide an indication of the corresponding part or process quality based on the analyzed signal signature. In such an example, the capability of providing a quality indication directly from the plate assembly eliminates any need to transmit large amounts of data from the sensor device. It allows for processing the output pass and fail decision internal to the sensor rather than having to provide signal signature information to a remotely located device. This allows for the process of making a quality determination to occur much faster.

The example of FIG. 3 includes a first output 64 that is useful for a first range of sensor device outputs associated with a first range of expected forces and a second output 66 that is useful for a second range of sensor device outputs associated with a second range of forces. In one example, the output 64 is used for high range force part forming processes and the output 66 is used in the case of a relatively lower force range for completing the part forming process.

For example, a low force is associated with small gauge wire crimping applications. In one example, a 90 kilogram peak force is associated with some smaller gauge wire crimping applications. The illustrated example allows for selecting the lower range output (e.g., 66). The electronics 60 have a calibration range scaled according to the selected output. In the case of a 90 kilogram peak force, the output 66 may have a calibration range scaled from 0 to 450 kilogram peak force. A calibration range for the output 64 may be like the typical calibration range of up to 2250 kilogram peak force, which is useful for example with standard wire gauge crimping applications that have a 650 kilogram expected peak force. Providing different calibration ranges for the different outputs 66 and 64 allows the example sensor device to effectively scale the output for various types of part forming processes including a wider variety of wire gauges used in crimping applications, for example. Additionally, providing multiple outputs 64 and 66 and correspondingly different calibration ranges allows for optimum flexibility when using the sensor device 30 and allows for quick changeover in a manufacturing environment when different part forming processes are carried out using the same machinery.

The multiple ranges for the outputs provide an output relative to force with sufficient amplitude to minimize the effect of induced noise associated with any cables used to connect the sensor device 30 to another device such as a computer, which may be several meters away. Using different output ranges in this example improves the signal-to-noise ratio.

One aspect of the outputs 64 and 66 in some examples is that they are configured as industry standard connectors that allow for coaxial cable connections, USB connections, Ethernet connections or serial bus connections, for example. Being able to customize the outputs 64 and 66 in this way allows the example sensor device to be directly connected to a manufacturing machine control system without the need for a separate monitor or analyzing device.

Another example arrangement is shown in FIGS. 4 and 5. In this example, instead of using individual piezoelectric polymer film sensor elements 34A and 34B, a single piezoelectric polymer film sensing element 34 is arranged between the plate portions 38 and 36. In this example, the plate 32 has a surface area extending between the edges of the plate. The piezoelectric polymer film 34 has outside dimensions (e.g., a surface area) that corresponds to a substantial portion of the surface area of the plate. In one example, the surface area of the piezoelectric polymer film 34 is entirely coextensive with the surface area of the plate 32. In another example, the area of the plate is slightly larger than that of the film 34. Because the film 34 is distributed across a substantial portion of the surface area of the plate, there is no concern with shunting or edge loading effects with this example arrangement. The relationship between the surface areas of the plate and film do not require the film to be on an outside surface of the plate to be “extending across,” “corresponding to” or “coextensive with” the surface area of the plate. Instead, those terms are used in this description to describe the desired dimensional relationship. As illustrated, in many embodiments, the piezoelectric polymer film 34 will be sandwiched between plate portions such that it is on the inside of a plate and not on an exposed “surface” of the plate.

In each of the above examples, the electronics 60 for processing signals from the at least one piezoelectric polymer film 34 were supported on the plate 32 of the sensor device 30. The example of FIG. 6 shows another arrangement where the electronics are separate from the plate 32. In this example, a connection 70 includes a coax cable, for example, for connecting a selected one of the outputs 64 or 66 with the processing electronics 72 that are supported separate from the plate 32. The electronics 72 process the signals from the piezoelectric polymer film to provide, for example, a signature indicating the forces associated with a part formation process that is useful for monitoring quality. The electronics 72 communicate with a separate computer device 74 in the illustrated arrangement to provide ongoing or historical quality analysis capabilities, for example.

The ability of the piezoelectric polymer film sensor element 34 or elements 34A and 34B and the ability to provide multiple range sensor outputs yields an output relative to force with sufficient amplitude to minimize the effect of induced noise associated with the connection 70. In some cases, the electronics 72 may be up to three meters away from the plate 32 and a coax cable used for such a connection may tend to introduce noise. Utilizing the approach of this description and a piezoelectric polymer film allows for improving the signal-to-noise ratio, which allows for the example device to be used for a wider range of manufacturing processes.

The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.

Claims

1. A sensor device, comprising: a plate adapted to be associated with a forming machine such that a force used during a forming operation is incident on the plate; andat least one piezoelectric polymer film supported on the plate, the film providing an electrical output indicative of the force incident on the plate.

2. The device of claim 1, comprising a plurality of piezoelectric polymer films supported on the plate.

3. The device of claim 2, wherein the plurality of piezoelectric polymer films are arranged symmetrically about a location on the plate that is expected to be where the incident force is most prominent.

4. The device of claim 3, wherein the plate comprises a scrap chute opening and the plurality of films are arranged symmetrically about the scrap chute opening.

5. The device of claim 2, wherein the multiple films provide a combined output indicative of the force incident on the plate.

6. The device of claim 5, wherein the combined output comprise a greater output value per unit force relative to an output of one of the films.

7. The device of claim 1, wherein the plate has a surface area and the at least one film has outside dimensions that correspond to at least a substantial portion of the surface area.

8. The device of claim 7, wherein the at least one piezoelectric polymer film is a single film.

9. The device of claim 7, wherein the film extends across the entire surface area of the plate.

10. The device of claim 1, comprising a signal processor supported on the plate for converting the output of the at least one film into a digital signal.

11. The device of claim 1, comprising a first output portion associated with the plate for providing an indication of the output of the at least one film in a first range; anda second output portion associated with the plate for providing an indication of the output of the at least one film in a second, different range.

12. The device of claim 11, wherein the indication of the first output portion is scaled using a first scaling level and the indication of the second output portion is scaled using a second, different scaling level.

13. The device of claim 12, wherein the first scaling level increases the indication of the first output portion when the first output portion is used to provide an indication of a force in a first range and the second scaling level adjusts the indication of the second output portion when the second output portion is used to provide an indication of a force in a second, higher range.

14. The device of claim 1, comprising a second plate adjacent the plate such that the at least one film is between the plate and the second plate and the film contacts both of said plates.

15. The device of claim 14, wherein the plates are electrically isolated from each other.

16. The device of claim 15, wherein the film isolates the plates from each other.

17. The device of claim 1, comprising a microprocessor at least partially supported by the plate, the microprocessor being configured to analyze the output of the film and to provide a corresponding indication of a quality associated with the force.