System and method for continuous mode force testing

Abstract

A method and system for testing a force or strain sensor in a continuous manner is described herein. The method employs a sensor, a test fixture, a force transducer, a mechanical actuator, and test instrument hardware and software to simultaneously record signal output from the sensor and force transducer as a function of time. The method provides time-synchronized events for recording data streams between, for example, a linear ramp of force on the sensor or displacement of the sensor, and for extracting performance characteristics from the data in post-test processing.

Description

[0001] Cross Reference to Related Applications

[0002] This application claims the benefit of U.S. Provisional Patent Application No. 62 / 854,422, filed May 30, 2019, and entitled “CONTINUOUS MODE FORCE TESTING,” the disclosure of which is expressly incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to testing of force sensors and strain gages for converting force or strain to electrical signals. BACKGROUND

[0004] In testing sensors such as force sensors and strain gages, it is often necessary to evaluate the response of the sensor over a range of input values to assess whether the performance meets the specifications. Current testing techniques require the application of a range of force or strain values and mechanically stabilizing each force or strain and waiting for the electrical signal to change to be stable before taking each measurement. The repetitive process of applying a force or strain, waiting for mechanical and electrical stabilization, measuring both the force or strain and the electrical signal, and applying an additional force or strain value is both time consuming and expensive.

[0005] Accordingly, there is a need in the related art for a less time consuming and less expensive testing method for force sensors and strain gages. SUMMARY

[0006] The present disclosure relates to a method of testing force sensors and strain gages, the method comprising applying a mechanical force or strain and measuring the electrical output of the sensor. Each force or strain sensor can include a flexure and one or more piezoresistive strain gages. In one embodiment, a mechanical force is applied (where the applied force is linearly ramped) while the electrical output of the force sensor and the amount of applied force are measured simultaneously. Synchronization events are introduced in the test sequence to allow for post processing and analysis of the data acquired through the various measurement channels. The method enables faster, less expensive, and more accurate acquisition of measurements for force sensors and strain gages.

[0007] An exemplary testing system is described herein. The system includes a test fixture configured to provide electrical connections to a force or strain sensor, a mechanical actuator configured to apply a force to the force or strain sensor, a force sensor configured to measure an amount of the force applied to the force or strain sensor, and a controller configured to operate the mechanical actuator and simultaneously record respective output signals from the force or strain sensor and the force sensor.

[0008] In some embodiments, the step of simultaneously recording respective output signals from the force or strain sensor and the load cell optionally comprises sampling the respective output signals in a burst mode, wherein the burst mode is defined by a sampling frequency and a sampling period.

[0009] In some embodiments, the respective output signals from the force or strain sensor are sampled at a first sampling frequency and a first sampling period. Additionally, the respective output signals from the load cell are optionally sampled at a second sampling frequency and a second sampling period. Optionally, the first sampling frequency and the second sampling frequency are the same or different.

[0010] Alternatively or additionally, the force or strain sensor comprises one or more piezoresistive transducers, piezoelectric transducers, or capacitive transducers.

[0011] Alternatively or additionally, the system further optionally comprises a robotic arm, wherein the mechanical actuator is optionally controlled by the robotic arm. For example, the robotic arm can be operatively connected to and controlled by the controller.

[0012] Alternatively or additionally, the respective output signals from the force or strain sensor and the load cell are stored in a memory of the controller.

[0013] Alternatively or additionally, the respective output signals from the force or strain sensor and the load cell are recorded as a function of time. In some embodiments, the controller is configured to operate the mechanical actuator to change the amount of force applied by the mechanical actuator from a first force value to a second force value, wherein the first force value and the second force value are different. Optionally, the controller is further configured to operate the mechanical actuator to: hold the first force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time; subsequently ramp the first force value to the second force value while recording the respective output signals from the force or strain sensor and the load cell as a function of time; and hold the second force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time. In some embodiments, the controller is further configured to operate the mechanical actuator to use the transition from the first force value to the ramped force and the transition from the ramped force to the second force value as a temporal data synchronization point between the respective output signals from the force or strain sensor and the load cell.

[0014] Alternatively or additionally, the system can optionally include a flexible substrate, wherein the force or strain sensor is soldered to the flexible substrate, and the force is applied to the flexible substrate by the mechanical actuator to create displacement and strain within the flexible substrate and strain within the force or strain sensor. In some embodiments, the respective output signals of the force or strain sensor are recorded by the controller through electrical wiring within the flexible substrate.

[0015] In some embodiments, the system optionally includes the force or strain sensor.

[0016] Also described herein are example methods for testing a force or strain sensor. The example methods include providing a test fixture configured to provide an electrical connection to the force or strain sensor; connecting the force or strain sensor to the test fixture; and operating a mechanical actuator to apply a force to the force or strain sensor. The example methods also include providing a force sensor configured to measure an amount of the force applied to the force or strain sensor, and simultaneously recording respective output signals from the force or strain sensor and the force sensor.

[0017] Additionally, the step of simultaneously recording respective output signals from the force or strain sensor and the force sensor includes sampling the respective output signals in a burst mode, wherein the burst mode is defined by a sampling frequency and a sampling period.

[0018] In some embodiments, the respective output signals from the force or strain sensor are sampled at a first sampling frequency and a first sampling period. Additionally, the respective output signals from the force sensor are sampled at a second sampling frequency and a second sampling period. Optionally, the first sampling frequency and the second sampling frequency are the same or different.

[0019] Alternatively or additionally, the force or strain sensor detects strain through a piezoresistive transducer, a piezoelectric transducer, or a capacitive transducer.

[0020] Alternatively or additionally, the mechanical actuator is optionally controlled by a robotic arm. For example, the robotic arm can be operatively connected to a computing device and controlled by the computing device.

[0021] Alternatively or additionally, the respective output signals from the force or strain sensor and the force sensor are optionally stored in a memory of a computing device.

[0022] Alternatively or additionally, the respective output signals from the force or strain sensor and the force sensor are optionally recorded as a function of time.

[0023] Alternatively or additionally, the method further includes varying the amount of the force applied by the mechanical actuator from a first force value to a second force value, where the first force value and the second force value are different. In some embodiments, the method further includes: holding the first force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time; subsequently ramping the first force value to the second force value while recording the respective output signals from the force or strain sensor and the load cell as a function of time; and holding the second force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time. Optionally, the method further includes using the transition from the first force value to the ramped force and the transition from the ramped force to the second force value as temporal data synchronization points between the respective output signals from the force or strain sensor and the load cell.

[0024] Alternatively or additionally, the force or strain sensor is soldered to a flexible substrate, and the force is applied by the mechanical actuator to the flexible substrate to produce displacement and strain within the flexible substrate and strain within the force or strain sensor. Additionally, the respective output signals of the force or strain sensor are recorded through electrical wiring within the flexible substrate.

[0025] Other systems, methods, features, and / or advantages will become apparent to one skilled in the art upon consideration of the following detailed description with reference to the accompanying drawings. It is intended that all such additional systems, methods, features, and / or advantages be included within this description, be within the scope of the claims. BRIEF DESCRIPTION OF DRAWINGS

[0026] The components in the drawings are not necessarily to scale relative to each other. In several views, like reference numerals designate corresponding parts throughout the several views. These and other features will become apparent upon reading the detailed description with reference to the accompanying drawings in which:

[0027] Figure 1 is an isometric view of the top of an example force sensor.

[0028] Figure 2 is Figure 1 is a cross-sectional view of the force sensor shown in

[0029] Figure 3 shows a cross-sectional view of another example force sensor soldered to a substrate, where a force is applied to the top of the force sensor.

[0030] Figure 4A cross-sectional view of another example force sensor welded to a substrate is shown, where force is applied to the bottom of the substrate.

[0031] Figure 5 A typical voltage output response of a force sensor relative to input force level is shown.

[0032] Figure 6 A force versus time relationship applied to a force sensor is shown, as measured by a force sensor according to embodiments described herein.

[0033] Figure 7 An example voltage output signal versus time of a force sensor experiencing the force profile shown in Figure 6

[0034] Figures 8A-8C An example of the relative timing between a force event applied to a force sensor Figure 8A ) and the resulting force sensor force output Figure 8C ) and force sensor voltage output Figure 8B ) is shown.

[0035] Figure 9 A relationship of voltage output versus force output measurements resulting from post-processing of force sensor voltage output and force sensor voltage output values and synchronization of force events (A and A' / B and B') is shown.

[0036] Figure 10 A cross-sectional view of a system for testing a force or strain sensor according to embodiments described herein is shown.

[0037] Figure 11 is a block diagram of an example computing device. DETAILED DESCRIPTION

[0038] The present disclosure can be more easily understood and further advantages and benefits can be obtained by reference to the following detailed description together with the appended drawings and is described in the context thereof. Prior to the disclosure and description of the apparatus, systems and / or methods, it is to be understood that the disclosure is not limited to the specific apparatus, systems and / or methods disclosed, and as such, it is of course contemplated to be able to vary and / or modify the disclosed apparatus, systems and / or methods. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0039] ​The following description is provided as enabling teachings. For this reason, the related art will be explained in terms of exemplary embodiments. Those skilled in the art will recognize and appreciate that many changes can be made to the embodiments, and that many fully functional systems, articles of manufacture, and methods can be made without departing from the scope of the present disclosure. Thus, the following description is not intended to limit the scope of the present disclosure.

[0040] As used throughout, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a force sensor" can include two or more such force sensors unless the context clearly indicates otherwise.

[0041] The term "comprising" and variations thereof as used herein are synonymous with the term "including" and variations thereof, and are open, non-limiting terms.

[0042] Ranges can be expressed herein as from "about" one particular value, and / or to "about" another particular value. When such ranges are recited, another aspect includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that each endpoint is significant, and that the use of "about" with respect to'any particular value means that the description encompasses the particular value plus or minus ten percent.

[0043] As used herein, the term "optional" or "optionally" means that the subsequently described event or circumstance can or can not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0044] In the present disclosure, the terms "force sensor" and "strain sensor" can be used to describe the sensor being tested. The disclosed systems and methods can be used to test a force sensor or a strain sensor. In some embodiments, the force or strain sensor is a microelectromechanical system ("MEMS") sensor.

[0045] The present disclosure relates to systems and methods for testing force or strain sensors. In the following examples, systems and methods are described with respect to testing force sensors. It should be understood that force sensor testing is provided as an example only. The present disclosure contemplates that the systems and methods described herein can be used to test strain sensors (or strain gauges). Reference is made to Figure 1 and Figure 2In some embodiments, the force sensor 10 includes a base 11 and electrical contacts 19. The electrical contacts 19 can be solder bumps, posts, or other electrically conductive contacts. It will be appreciated that the electrical contacts 19 provide a means for applying a voltage to the force sensor 10 and / or recording a voltage from the force sensor. A contact surface 15 is present along a top surface of the base 11 for receiving an applied force F and transmitting the force F to at least one mechanical flexure 16.

[0046] Referring again to Figure 1 and Figure 2 , the force sensor can include one or more diffused, deposited, or implanted sensing elements 22 on a bottom surface 18 of the base 11. The bottom surface 18 is opposite the contact surface 15. The one or more sensing elements 22 can optionally include piezoresistive transducers, although the present disclosure contemplates the use of other transducer types, such as piezoelectric or capacitive transducers. It will be appreciated that Figure 1 and Figure 2 the number and / or arrangement of sensing elements 22 shown in Figure 1 and Figure 2 is provided by way of example only. The present disclosure contemplates that the force sensor can include more, fewer, and / or different arrangements of sensing elements than shown in Figure 1 and Figure 2 . As a result of the strain induced in the at least one mechanical flexure 16 in proportion to the force F, a local strain is created on the sensing elements 22 such that the sensing elements 22 experience compression or tension, depending on their particular orientation. As the sensing elements 22 compress and tension, their resistivity changes. The change in resistivity is proportional to the force F applied to the contact surface 15. To determine the force F, the resistivity can be measured, and the proportional relationship between resistivity and force can be used to calculate the force. The resistivity can be measured using a circuit configured to measure the resistivity, for example, a Wheatstone bridge circuit 23 containing the sensing elements 22 produces a differential voltage proportional to the applied force F on the contact surface 15, according to the embodiments described herein.

[0047] It will be appreciated that Figure 1 and Figure 2 the force sensor 10 shown in Figure 1 and Figure 2force sensors other than those shown in the figures. Exemplary MEMS force sensors that can be tested using the systems and methods of the present disclosure are described in detail in U.S. Patent No. 9,487,388, issued November 8, 2016, and entitled “Ruggedized MEMS Force Die”; U.S. Patent No. 9,493,342, issued November 15, 2016, and entitled “Wafer Level MEMS Force Dies”; U.S. Patent No. 9,902,611, issued February 27, 2018, and entitled “Miniaturized and ruggedized wafer level mems force sensors”; U.S. Patent No. 10,466,119, issued November 5, 2019, and entitled “Ruggedized wafer level mems force sensor with a tolerance trench”; WO2018 / 148503, published August 16, 2018, and entitled “INTEGRATED DIGITAL FORCE SENSORS AND RELATED METHODS OF MANUFACTURE”; and WO2018 / 148510, published August 16, 2018, and entitled “INTEGRATED PIEZORESISTIVE AND PIEZOELECTRIC FUSION FORCE SENSOR”, the disclosures of which are incorporated by reference in their entireties.

[0048] Figure 3 and Figure 4 A force sensor 30 according to another embodiment described herein is illustrated. Optionally, the force sensor 30 is soldered to a substrate 31 by solder balls 32. Optionally, the substrate 31 can be a flexible substrate, and electrical wiring can be positioned within the flexible substrate. The present disclosure contemplates that the force sensor 30 can be any force sensor, including the MEMS force sensors described above. As Figure 3 As shown in the figure, the force sensor 30 can be activated with a force F from the top surface to measure the force F and output an electrical signal proportional to the applied force. In this embodiment, the substrate is optionally held in place with a backing material or other support material.

[0049] Referring to Figure 4The force sensor 30 can be activated, optionally, by applying a force F from the bottom surface of the substrate 31. The force F can induce a displacement and strain in the substrate 31, which in turn can impart the strain to the force sensor 30 through the solder balls 32. In this embodiment, the substrate 31 is optionally somewhat flexible, while the top surface of the sensor 30 is optionally not constrained by any hard surface. The force sensor 30 can take the strain and can output an electrical signal proportional to the amount of strain it is subjected to due to the force F.

[0050] Figure 5 A graph depicting the relationship of a typical output voltage signal of a force sensor (e.g., such as the force sensor described above with respect to Figures 1-4 The force sensor test is conventional in that the force value is set and held constant while the output of the force sensor is measured. This process is repeated with multiple force level increments to establish a response curve of the sensor (i.e., the dashed line in Figure 5 At each applied force value, the output of the force sensor is allowed to stabilize before moving to the next incremental force value. The response curve represents the relationship of the voltage output (y-axis) to the applied force (x-axis). The present disclosure contemplates that the force response of a force or strain sensor is monotonic, e.g., the voltage output never decreases as the value of the applied force increases. Figure 5 The linear force response shown in FIG. 1 is provided as an example only. It should be understood that the force response curve of a force or strain sensor can be non-linear. This conventional test method is time consuming because changing the applied force induces electrical and mechanical noise, which requires a stabilization time or averaging to reduce the noise and achieve measurement accuracy.

[0051] Figure 6 A graph illustrating the force applied to a force sensor as a function of time according to embodiments described herein is illustrated in FIG. 2. In Figure 6 The applied force (or voltage output) is measured by a force sensor. As described herein, a force sensor is a transducer that converts an applied force into a measurable output voltage. In other words, the voltage output of a force sensor is indicative of the force applied to the force sensor. The applied force is held at a fixed value Fi until time ti. At time ti, which corresponds to point A in the graph, the force begins to ramp up over time. As discussed below, the force is continuously increased from Fi to F2 between point A (at time ti) and point B (at time t2). In Figure 6 The force ramps up (e.g., increases linearly) over time in FIG. 2. It should be understood that the applied force that increases linearly from time ti is provided as an example only. The present disclosure contemplates that the applied force that increases from time ti can increase in a non-linear manner. Additionally, it should be understood that the force can be ramped up (e.g., increased) in a non-linear manner from time ti. Figure 6The rate of increase shown is provided as an example only, and other rates of increase are possible. The force continuously increases at a slope to point B in the graph, and from time t2, the force remains at a fixed value F2. Figure 6 In this context, F2 is greater than F1. It should be understood that the values ​​of F1 and F2, as well as times t1 and t2 and their relationship, are provided only as examples. Furthermore, Figure 6 The example uses a force that increases with elevation. It should be understood that the force can decrease over time, for example, between F2 and F1. Figure 6 In this diagram, the x-axis represents time, and the y-axis represents the applied force. It should be understood that... Figure 6 The y-axis in the diagram represents the voltage output of the force sensor, which indicates the applied force.

[0052] Figure 7 Examples of experiences Figure 6 The voltage output of a linear force sensor is illustrated in the diagram. It should be understood that the force response of a force or strain sensor does not need to be linear. The response of a force or strain sensor, whether linear or nonlinear, is expected to be monotonic. Figure 7 The linear force response shown is provided as an example only. Figure 7 In this configuration, the voltage output is measured by a force sensor. In other words, Figure 7 The x-axis in the diagram represents time, and Figure 7 The y-axis in the diagram represents the voltage output of the force sensor. When the applied force F1 is constant, there is a constant voltage output V1. When the applied force is... Figure 6 When point A in the equation begins to ascend linearly, from... Figure 7 Starting from point A', the voltage output changes accordingly. This occurs... Figure 7 The time t1' in the middle. It should be understood that, Figure 7 The rate of increase shown is provided as an example only, and other rates of increase are possible. Furthermore, there is a delay between the input force and the output voltage of the force sensor. For example, this delay may be caused by delays in the signal path and / or by the force sensor itself. Figure 6 ) and force sensor ( Figure 7 This is caused by differences in signal path length. Therefore, Figure 7 The time t1' in Figure 6 The time t1 is different. Similarly, Figure 6 t2 and Figure 7 The t2' in the text is different.

[0053] Due to force Figure 6 As shown, the voltage increases linearly, therefore the force sensor's voltage output responds proportionally, such as... Figure 7 The middle point is located between points A' and B', as shown. (Reference) Figure 7The sensor's voltage output increases until it reaches point B', corresponding to the applied constant force level F2. This occurs... Figure 7 The time t2' in the signal path. After point B', the voltage output remains constant at the voltage V2 corresponding to the constant force F2. Similarly, the delay may be caused by the delay in the signal path and / or the force sensor ( Figure 6 ) and force sensor ( Figure 7 This is caused by the difference in signal path length.

[0054] Figures 8A-8C An example of the relative timing between events and measurements according to the implementation described herein is shown. Figure 8A Indicating force sensor (e.g., Figures 1-4 The timing of force application by the force sensor in any of the figures is illustrated as a linear increase in force from point A to point B. The applied force increases continuously over time between points A and B (e.g., in contrast to incremental changes or discontinuous steps). As described above, Figure 6 and Figure 7 The applied force and force response are provided as examples only, showing a linear increase in force. Figure 8A As shown, the applied force remains constant before point A and after point B. Between points A and B, the applied force continuously increases from F1 to F2. Figure 8B The timing of the voltage measurement from the force sensor (also referred to herein as the "force sensor output") is illustrated. According to... Figures 8A-8C In the embodiment illustrated, the system is configured to sample using a "burst mode." In "burst mode," the sensor and force sensor are sampled in a "burst," where each burst includes multiple voltage measurements (e.g., from the force sensor or force measurement sensor) acquired in each "burst cycle." Figures 8A-8C In the diagram, vertical arrows represent samples, and the spacing between the vertical arrows represents the sampling period. The sensor output can be tuned. Figure 8B ) and force sensor output ( Figure 8C The sampling rate is adjusted to reduce measurement noise during single burst mode readouts, for example, by averaging multiple voltage measurements acquired in a burst. Additionally, the burst period is not fixed and can be adjusted to take into account motor speed (e.g., the driver of a mechanical actuator), sensor output sensitivity, and / or other parameters specific to a given measurement implementation. Figures 8A-8CAs shown, multiple burst measurements are acquired from each of the force sensor and the force measurement sensor before points A and A', between points A / A' and B / B', and after points B and B'. It should be understood that multiple burst measurements are acquired from each of the force sensor and the force measurement sensor as the applied force continuously increases between points A / A' and B / B'. In other words, according to... Figures 8A-8C In the embodiment shown, the applied force does not increase incrementally (e.g., gradually) between point A / A' and point B / B', where there is a pause in the measurement at the incremental step. Figure 8C The timing of a measurement from a force sensor (also referred to herein as the "force sensor output") is illustrated, quantizing the force applied to the force sensor as a function of time. In burst mode, the force sensor is also measured with the force sampling period and the burst period indicated by the time between small vertical arrow groups. As discussed above, the force sensor output can be tuned ( Figure 8C The sampling rate is adjusted to reduce measurement noise during single burst mode readouts, for example, by averaging multiple voltage measurements acquired in the burst. Additionally, the burst period is not fixed and can be adjusted to take into account motor speed (e.g., the driver of a mechanical actuator), force sensor output sensitivity, and / or other parameters specific to a given measurement implementation. Different combinations of force sensor, force sensor, sampling mode, and sampling period are possible according to the embodiments described herein. For example, output data from the force sensor can be sampled at a first sampling frequency / period, and output data from the force sensor can be sampled at a second sampling frequency / period. According to some embodiments described herein, the force sensor sampling period and the force sensor sampling period can be the same. According to other embodiments, the force sensor sampling period and the force sensor sampling period can be different. Alternatively or additionally, the force sensor sampling frequency and the force sensor sampling frequency can be the same or different.

[0055] The actual timing of signal events between force sensor measurements and force sensor readings is typically not synchronized, but occurs with some relative delay between different signal paths. Figure 8C The value below is indicated as Δt relative to the signal delay. (This is in the context of the preceding text.) Figure 6 and Figure 7After measuring and recording the force sensor and force sensor voltage output signals using the sequence shown (e.g., fixing the first force (F1) until time t1 / t1', then increasing the force up to time t2 / t2', then fixing the second force (F2)), the signal data can be post-processed to map events at the start and end of the force up. Points A / A' and B / B' are used as temporal data synchronization points. For example, the start of the increase in the force sensor voltage output signal (e.g., at...) Figure 6 The time t1 in the equation is mapped to the start of the increase in the force sensor voltage output signal (e.g., at the beginning of the increase). Figure 7 The time t1' in the middle), and similarly the stability of the force sensor voltage output (e.g., in the time t1') is measured, and the stability of the force sensor voltage output is similarly measured (e.g., in the time t1') is measured. Figure 6 The time t2 in the equation is mapped to the stability of the force sensor voltage output (e.g., in the time t2). Figure 7 The time t2' in the equation is used to obtain the force sensor voltage output as a function of the force sensor voltage output. The measurement time of a signal path can be appropriately shifted or scaled so that the start and end times of the force ramp coincide between the force sensor voltage output and the force sensor voltage output. In some implementations, the force sensor and the force sensor voltage are sampled at the same rate, such that after scaling the time on a variable to match the start and stop events, intermediate points can also be scaled by the same factor so that the values ​​match one-to-one between the force sensor output and the sensor voltage output.

[0056] Turning point (e.g., Figure 6 and Figure 7 Points A / A' and B / B' in the diagram can be used as time synchronization points. It should be understood that the number of synchronization points and / or the relationship between them is provided only as an example. For instance, by synchronizing the time at which the force sensor output begins to change with the point at which the force sensor output begins to change, two graphs can be synchronized, thus taking into account any time delay between the outputs from the force sensor and the force measurement sensor. Therefore, the force sensor output voltage can be determined as a function of the force sensor force measurement value. By scaling the measurement time of a signal path, the force sensor voltage output, or the force sensor voltage measurement output and mapping the start and stop force ramp events, the force sensor voltage output can be determined as a function of the force sensor force measurement value, thus providing the desired relationship between the signal output and the applied force measurement value, such as... Figure 9 As shown in the diagram. This can be achieved without repeating multiple force level increments and measurements, as described above regarding... Figure 5 The conventional techniques discussed establish the response curve of the force sensor.

[0057] Figure 10 A cross-sectional view of a system used for testing force or strain sensors is shown. Figure 10In particular embodiments, the system includes a test fixture 44, a mechanical actuator 45, and a force sensor 46. The system also includes a controller (e.g., a computing device 1100 as shown in FIG. 11) operably coupled to the mechanical actuator 45 and the force sensor 46. Additionally, the controller is operably coupled to the force sensor 40 via the test fixture 44. The present disclosure contemplates that the force sensor 40 can be any of the force sensors described above, or another other type of force or strain sensor. The controller can be coupled to the mechanical actuator 45, the force sensor 46, and / or the force sensor 40 by one or more communication links. The present disclosure contemplates that the communication links are any suitable communication links. For example, the communication links can be implemented by any medium that facilitates the exchange of data, including, without limitation, wired, wireless, and optical links. Figure 11 In particular embodiments, the system includes a test fixture 44, a mechanical actuator 45, and a force sensor 46. The system also includes a controller (e.g., a computing device 1100 as shown in FIG. 11) operably coupled to the mechanical actuator 45 and the force sensor 46. Additionally, the controller is operably coupled to the force sensor 40 via the test fixture 44. The present disclosure contemplates that the force sensor 40 can be any of the force sensors described above, or another other type of force or strain sensor. The controller can be coupled to the mechanical actuator 45, the force sensor 46, and / or the force sensor 40 by one or more communication links. The present disclosure contemplates that the communication links are any suitable communication links. For example, the communication links can be implemented by any medium that facilitates the exchange of data, including, without limitation, wired, wireless, and optical links.

[0058] The test fixture 44 can be made of (or coated with) an insulating material and include one or more electrical connections 43. Optionally, as shown in Figure 10 The electrical connections 43 are disposed in a recess of the test fixture 44, where the recess is configured to fit the force sensor 40, as shown in Figure 10 The number, size, shape, and / or arrangement of the electrical connections 43 in Figure 11 The present disclosure contemplates that the force sensor 40 can be any of the force sensors described above, or another other type of force or strain sensor. The controller can be coupled to the mechanical actuator 45, the force sensor 46, and / or the force sensor 40 by one or more communication links. The present disclosure contemplates that the communication links are any suitable communication links. For example, the communication links can be implemented by any medium that facilitates the exchange of data, including, without limitation, wired, wireless, and optical links. Figure 7 and Figure 8B as shown in FIG. 11) operably coupled to the mechanical actuator 45 and the force sensor 46. Additionally, the controller is operably coupled to the force sensor 40 via the test fixture 44. The present disclosure contemplates that the force sensor 40 can be any of the force sensors described above, or another other type of force or strain sensor. The controller can be coupled to the mechanical actuator 45, the force sensor 46, and / or the force sensor 40 by one or more communication links. The present disclosure contemplates that the communication links are any suitable communication links. For example, the communication links can be implemented by any medium that facilitates the exchange of data, including, without limitation, wired, wireless, and optical links.

[0059] The system also includes a mechanical actuator 45. The mechanical actuator 45 is configured to apply a force to the force sensor 40. For example, the mechanical actuator 45 can be a movable rigid body. The mechanical actuator 43 can be made of a hard plastic (e.g., an acetal homopolymer such as DELRIN), a metal (e.g., aluminum, stainless steel, etc.), or an elastomeric material (e.g., silicone rubber). The present disclosure contemplates that the size and / or shape of the mechanical actuator is variable. For example, the mechanical actuator 45 can have a flat surface and / or a rounded protrusion. Alternatively or additionally, the mechanical actuator 45 can be larger or smaller than the size of the force sensor 40. Optionally, the mechanical actuator 45 is approximately the same size as the force sensor 40. The mechanical actuator 45 can be controlled to be in contact with the surface of the force sensor 40 and apply a force F3, which can vary over time as described herein. For example, the mechanical movement can be controlled by one or more electric motors, such as a stepper motor or a servo motor. In some embodiments, the system optionally includes a robotic arm, and the mechanical actuator 45 is operatively coupled to the robotic arm. For example, the mechanical actuator 45 can be attached to a robotic end effector. The robotic arm can be configured to control the movement (e.g., trajectory, position, orientation, etc.) of the mechanical actuator 45 relative to the test fixture 44, such that the mechanical actuator 45 can apply a variable force to the force sensor 40. As described above, the mechanical movement can be controlled by one or more electric motors. Robotic product testing systems are known in the art and therefore are not described in further detail herein.

[0060] Additionally, the system includes a force transducer 46. A force transducer is a transducer that converts force into a measurable electrical output (e.g., voltage). A strain gauge is one exemplary type of force transducer. It should be understood that other types of force transducers can be used in the system described herein. Force transducers are known in the art and therefore are not described in further detail herein. The force transducer 46 can be arranged in series with the mechanical actuator 45. The force F3 applied by the mechanical actuator 45 can be measured by the force transducer 46. Optionally, the force transducer 46 can be directly or indirectly attached to the mechanical actuator 45. Optionally, the force transducer 46 is not attached to the mechanical actuator 45. It should be understood that Figure 10 The arrangement of the force transducer 46 in FIG. 4 is provided as an example only.

[0061] As described herein, Figure 10 The applied force F3 in FIG. 4 can vary over time. For example, the mechanical actuator 45 can be controlled to apply a first force (e.g., Figure 6 a constant force F1 in FIG. 4) while simultaneously recording from the force sensor 40 (e.g., Figure 7 before time t1’) and the force transducer 46 (e.g., Figure 6the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 6 Figure 7 the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 6 Figure 6 the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 7 Figure 6 the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 6 Figure 7 the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 6 Figure 7 the corresponding output signals from force sensor 40 (e.g., at times t1 and t2) and load cell 46 (e.g., at times t1' and t2'). The mechanical actuator 45 can be further controlled to subsequently apply the second force (e.g., constant force F2 in Figure 9 This relationship between force sensor output voltage and applied force is shown, for example,

[0062] It should be appreciated that the logical operations described herein with respect to the various figures can be implemented (1) as a sequence of computer implemented acts or program modules running on a computing device (e.g., a computing device described in Figure 11 FIG. 2) ; (2) as interconnected machine logic circuits or circuit modules (i.e., hardware) within the computing device; and / or (3) a combination of both. Thus, the logical operations discussed herein are not limited to any particular combination of hardware and software. The implementation is a matter of choice dependent on the performance and other requirements of the computing device. The logical operations described herein are therefore implemented in various ways, as operations, structural devices, acts or modules. These operations, structural devices, acts and modules can be implemented in software, firmware, special purpose digital logic, and any combination thereof. It should also be appreciated that more or fewer operations can be performed than shown in the figures and described herein. These operations can also be performed in a different order than those described herein.

[0063] Referring to FIG. 1 Figure 11 ​​​​​The example computing device 1100 illustrates an example computing device on which the methods described herein can be implemented. The computing device 1100 can be operatively coupled to the mechanical actuators and force sensors described above and configured to control the application of force and record output data (e.g., output signals) from the force sensors. In addition, the computing device 1100 can be, for example, operatively coupled to the force sensors described above and configured to record output data (e.g., output signals) from the force or strain sensors. It should be appreciated that the example computing device 1100 is only one example of a suitable computing environment on which the methods described herein can be implemented. Optionally, the computing device 1100 can be a well-known computing system, including but not limited to a personal computer, a server, a handheld or laptop device, a multiprocessor system, a microprocessor-based system, a network personal computer (PC), a minicomputer, a mainframe computer, an embedded system, and / or a distributed computing environment comprising a plurality of any of the above systems or devices. A distributed computing environment enables remote computing devices connected to a communications network or other data transmission medium to perform various tasks. In a distributed computing environment, program modules, applications, and other data can be stored on local and / or remote computer storage media.

[0064] In its most basic configuration, computing device 1100 typically includes at least one processing unit 1106 and system memory 1104. Depending on the exact configuration and type of computing device, the system memory 1104 can be volatile (such as random access memory (RAM)), non-volatile (such as read-only memory (ROM), flash memory, etc.), or some combination of the two. This most basic configuration is illustrated in Figure 11 by dashed line 1102. Processing unit 1106 can be a standard programmable processor that carries out the operations of computing device 1100 by performing arithmetic and logical operations. Computing device 1100 can further include a bus or other communication mechanism for communicating information among the components of computing device 1100.

[0065] Computing device 1100 can have additional features / functionality. For example, computing device 1100 can include additional storage such as removable storage 1108 and non-removable storage 1110 including, but not limited to, magnetic or optical disks or tape. Computing device 1100 can further include a network connection 1116 that allows the device to communicate with other devices. Computing device 1100 can further have input device(s) 1114 such as a keyboard, mouse, touchscreen, etc. Output device(s) 1112 such as a display, speakers, printer, etc. can also be included. Additional devices can be connected to the bus in order to facilitate data communication in computing device 1100. All these devices are well known in the art and need not be discussed at length here.

[0066] The processing unit 1106 can be configured to execute program code encoded in tangible computer-readable media. Tangible computer-readable media refer to any media that can provide data that cause the computing device 1100 (i.e., a machine) to operate in a particular fashion. Various computing devices can be utilized to provide instructions to the processing unit 1106 for execution. Example tangible computer-readable media can include, but are not limited to, volatile media, non-volatile media, removable media, and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules, or other data. The system memory 1104, removable storage 1108, and non-removable storage 1110 are all examples of tangible computer storage media. Example tangible, computer-readable recording media include, but are not limited to, an integrated circuit (e.g., an integrated circuit chip or chipset), a hard disk, an optical disk, a magneto-optical disk, a floppy disk, a magnetic tape, a holographic storage medium, a solid-state device, RAM, ROM, electrically erasable program read-only memory (EEPROM), flash memory or other memory technology, a CD-ROM, digital versatile disks (DVD), or other optical storage, a magnetic cassette, a magnetic tape, a magnetic disk storage or other magnetic storage devices.

[0067] In example implementations, the processing unit 1106 can execute program code stored in the system memory 1104. For example, the bus can carry data to the system memory 1104 from which the processing unit 1106 receives and executes instructions. The data received by the system memory 1104 can optionally be stored on the removable storage 1108 or the non-removable storage 1110 before or after execution by the processing unit 1106.

[0068] It should be understood that the various techniques described herein can be implemented in connection with hardware or software or, where appropriate, with a combination thereof. Thus, the methods and apparatus of the presently disclosed subject matter, or certain aspects or portions thereof, can take the form of program code (i.e., instructions) embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other machine-readable storage medium wherein, when the program code is loaded into and executed by a machine, such as a computing device, the machine becomes an apparatus for practicing the presently disclosed subject matter. In the case of program code execution, the computing device generally includes a processor, a storage medium readable by the processor (including volatile and non-volatile memory and / or storage elements), at least one input device, and at least one output device. One or more programs can implement or utilize the processes described in connection with the presently disclosed subject matter, e.g., through the use of an application programming interface (API), reusable controls, or the like. Such programs can be implemented in a high level procedural or object oriented programming language to communicate with a computer system. However, the program(s) can be implemented in assembly or machine language, if desired. In any case, the language can be a compiled or interpreted language, and combined with hardware implementations.

[0069] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as example forms of implementing the claims.

Claims

1. A system for testing a force or strain sensor, the system comprising: a test fixture configured to provide an electrical connection to a force or strain sensor, wherein the force or strain sensor comprises: a base defining a top surface and a bottom surface disposed opposite the top surface; one or more diffused, deposited, or implanted sensing elements on the bottom surface of the base; and electrical contacts attached to the bottom surface of the base and extending beyond the bottom surface of the base; a mechanical actuator configured to apply a force to the force or strain sensor; a force sensor configured to measure an amount of the force applied to the force or strain sensor; a controller configured to operate the mechanical actuator and contemporaneously record respective output signals from the force or strain sensor and the force sensor; and a flexible substrate, wherein the bottom surface of the force or strain sensor is soldered to the flexible substrate, and a force is applied to the flexible substrate by the mechanical actuator to produce a displacement and a strain within the flexible substrate and a strain within the force or strain sensor while the top surface of the force or strain sensor is unconstrained by any hard surface.

2. The system of claim 1, wherein contemporaneously recording respective output signals from the force or strain sensor and the force sensor comprises sampling the respective output signals in a burst mode, wherein the burst mode is defined by a sampling frequency and a sampling period.

3. The system of claim 2, wherein the respective output signals from the force or strain sensor are sampled at a first sampling frequency and a first sampling period.

4. The system of claim 3, wherein the respective output signals from the force sensor are sampled at a second sampling frequency and a second sampling period.

5. The system of claim 4, wherein the first sampling frequency and the second sampling frequency are the same.

6. The system of claim 4, wherein the first sampling frequency and the second sampling frequency are different.

7. The system of claim 1, wherein the force or strain sensor comprises one or more piezoresistive, piezoelectric, or capacitive transducers.

8. The system of claim 1, further comprising a robotic arm, wherein the mechanical actuator is controlled by the robotic arm.

9. The system of claim 8, wherein the robotic arm is operably connected to and controlled by the controller.

10. The system of claim 1, wherein the respective output signals recorded by the controller are stored in a memory of the controller.

11. The system of claim 1, wherein the respective output signals from the force or strain sensor and the force sensor are recorded as a function of time.

12. The system of claim 1, wherein the controller is configured to operate the mechanical actuator to continuously vary an amount of the force applied by the mechanical actuator from a first force value to a second force value, wherein the first force value and the second force value are different.

13. The system of claim 12, wherein the controller is further configured to: hold the first force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time, subsequently ramp the first force value to the second force value while recording the respective output signals from the force or strain sensor and the load cell as a function of time, and hold the second force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time.

14. The system of claim 13, wherein the controller is further configured to use the transition from the first force value to the ramped force and the transition from the ramped force to the second force value as temporal data synchronization points between the respective output signals from the force or strain sensor and the load cell.

15. The system of claim 1, wherein the respective output signals of the force or strain sensor are recorded by the controller through electrical wiring within the flexible substrate.

16. The system of claim 1, wherein the system includes the force or strain sensor.

17. A method for testing a force or strain sensor, the method comprising: providing a test fixture configured to provide electrical connections to the force or strain sensor, wherein the force or strain sensor comprises: a base defining a top surface and a bottom surface disposed opposite the top surface; one or more diffused, deposited, or implanted sensing elements on the bottom surface of the base; and electrical contacts attached to the bottom surface of the base and extending beyond the bottom surface of the base; connecting the force or strain sensor to the test fixture; operating a mechanical actuator to apply a force to the force or strain sensor; providing a load cell configured to measure an amount of the force applied to the force or strain sensor; simultaneously recording respective output signals from the force or strain sensor and the load cell; and wherein the bottom surface of the force or strain sensor is soldered to a flexible substrate, and force is applied to the flexible substrate by the mechanical actuator to create displacement and strain within the flexible substrate and strain within the force or strain sensor while the top surface of the force or strain sensor is unconstrained by any hard surface.

18. The method of claim 17, wherein simultaneously recording respective output signals from the force or strain sensor and the load cell comprises sampling the respective output signals in a burst mode, wherein the burst mode is defined by a sampling frequency and a sampling period.

19. The method of claim 18, wherein the respective output signals from the force or strain sensor are sampled at a first sampling frequency and a first sampling period.

20. The method of claim 19, wherein the respective output signals from the load cell are sampled at a second sampling frequency and a second sampling period.

21. The method of claim 20, wherein the first sampling frequency and the second sampling frequency are the same.

22. The method of claim 20, wherein the first sampling frequency and the second sampling frequency are different.

23. The method of claim 17, wherein the force or strain sensor detects strain through a piezoresistive transducer, a piezoelectric transducer, or a capacitive transducer.

24. The method of claim 17, wherein the mechanical actuator is controlled by a robotic arm.

25. The method of claim 24, wherein the robotic arm is operably connected to a computing device and controlled by the computing device.

26. The method of claim 17, wherein the respective output signals from the force or strain sensor and the load cell are stored in a memory of a computing device.

27. The method of claim 17, wherein the respective output signals from the force or strain sensor and the load cell are recorded as a function of time.

28. The method of claim 17, further comprising continuously varying an amount of the force applied by the mechanical actuator from a first force value to a second force value, wherein the first force value and the second force value are different.

29. The method of claim 28, further comprising: holding the first force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time; subsequently ramping the first force value to the second force value while recording the respective output signals from the force or strain sensor and the load cell as a function of time; and holding the second force value constant while recording the respective output signals from the force or strain sensor and the load cell as a function of time.

30. The method of claim 29, further comprising using transitions from the first force value to a ramped force and from the ramped force to the second force value as temporal data synchronization points between the respective output signals from the force or strain sensor and the load cell.

31. The method of claim 17, wherein the respective output signals of the force or strain sensor are recorded through electrical wiring within the flexible substrate. ​

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