Force sensor measurement damping compensation

Abstract

A test system (100) includes a force sensor (102), a support (108), a sensor (124), and a controller (120). The force sensor (102) is configured to generate a force output (114) indicative of a force applied to the sensor (102) and includes an active side (116) and a fixed side (118). The support (108) is connected to the force sensor (102) and is configured to support a test sample. The sensor (124) is configured to generate a sensor output (122) indicative of a speed of the movable side (116) relative to the fixed side (118). The controller (120) is configured to receive the force output (114) and the sensor output (122), calculate a damping compensation based on the sensor output (122), a damping constant estimate associated with a motion of the sensor (102) and the support (108), and a secondary mass including a mass of the sensor (102) and the support (108), and generate a corrected force measurement based on the force output (114) and the damping compensation.

Description

TECHNICAL FIELD

[0001] Embodiments of the present disclosure relate generally to force measurements produced by force sensors, and more particularly to damping compensation of such force measurements. BACKGROUND

[0002] The following discussion is merely provided for general background information and is not intended to be used as aid in determining the scope of the claimed subject matter.

[0003] Force measurements are typically performed using force or pressure sensors (hereinafter referred to as "force sensors"). Such force sensors are used, for example, in various test systems, such as automotive test systems, material test systems, elastomer test systems, and other test systems, for measuring forces exerted on a test specimen in response to actuator-driven forces or motions applied to the test specimen.

[0004] Force measurements produced by force sensors can contain inertial errors related to the acceleration of secondary masses, which are different from the test specimen, that are produced in response to the forces or motions applied to the test specimen. The secondary masses can include, for example, the mass of movable components of the force sensor and the mass of components used to support the test specimen.

[0005] To improve the accuracy of force measurements, compensation can be applied to correct for inertial errors by applying an acceleration compensation that is based on an estimate of the acceleration of the secondary masses.

[0006] Other mechanical errors that can be present in force measurements include mechanical damping errors. One such mechanical damping error is viscous material damping that is produced during the motion of the secondary masses. Conventional techniques for generating force measurements using force sensors do not account for such mechanical damping errors. SUMMARY

[0007] This summary is intended to provide a brief overview of some concepts related to the subject matter described herein. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementation that solves any or all disadvantages noted in the background.

[0008] Embodiments of the present disclosure are directed to methods and systems for correcting mechanical damping errors in force measurements produced by force sensors in test systems, or methods and systems for correcting other forms of damping that shunt a portion of the force in parallel with the sensor sensing mechanism.

[0009] One embodiment of the system includes a force sensor, a support, a sensor, and a controller. The force sensor is configured to generate a force output indicative of a force applied to the sensor. The support is connected to the force sensor and is configured to support a test specimen. The force sensor includes an active side and a fixed side. The sensor is configured to generate a sensor output indicative of a velocity of the active side of the force sensor relative to the fixed side. The controller is configured to receive the force output and the sensor output, compute a damping compensation based on the sensor output, a damping constant estimate associated with a damping characteristic of the sensor and the support, and a secondary mass comprising a mass of the sensor and the support, and generate a corrected force measurement based on the force output and the damping compensation.

[0010] Other embodiments relate to methods of using embodiments of the system to compensate for mechanical damping errors in force sensor measurements. In one embodiment of a method for correcting force measurements in a test system, a test specimen is supported by a support connected to a force sensor. A force output is generated using the force sensor, the force output being indicative of a force applied to the force sensor. A sensor output is generated indicative of a velocity of an active side of the force sensor relative to a fixed side of the force sensor. A controller receives the force output and the sensor output and computes a damping compensation based on the sensor output, a damping constant estimate associated with a damping characteristic of the force sensor and the support, and a secondary mass comprising a mass of the force sensor and the support. A corrected force measurement is generated using the controller based on the force output and the damping compensation.

[0011] This Summary is intended to introduce in simplified form a series of concepts that are further described below in the of Specific Embodiments. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to determine the scope of the claimed subject matter. The claimed subject matter is not limited to implementing BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 is a simplified schematic diagram of an example of a test system or a portion thereof in accordance with an embodiment of the present disclosure.

[0013] Figure 2 is a schematic diagram of an example of a controller in accordance with an embodiment of the present disclosure.

[0014] Figure 3 is a simplified schematic diagram of an example of a test system or a portion thereof in accordance with an embodiment of the present disclosure. Figure 1 is a schematic diagram of an example of a test system in the form of an elastomer test system in accordance with an embodiment of the present disclosure.

[0015] Figure 4 is a simplified schematic diagram of an example of a test system or a portion thereof in accordance with an embodiment of the present disclosure. Figure 1and Figure 3 simplified free-body diagram of an example model of the test system shown.

[0016] Figure 5 is a simplified schematic diagram of an example test system according to embodiments of the disclosure.

[0017] Figure 6 is an isometric view of an example of a vehicle restraint system of a car driving situation simulator according to embodiments of the disclosure.

[0018] Figure 7 is a simplified schematic diagram of an example test system according to embodiments of the disclosure. Figure 5 the test system shown and Figure 6 simplified free-body diagram of an example model of aspects of the restraint system shown. DETAILED DESCRIPTION

[0019] Embodiments of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. Like reference numerals can be used to identify like elements throughout the several views. Various embodiments of the disclosure can, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

[0020] As noted above, embodiments of the present disclosure generally relate to damping compensation of force measurements in a test system having a test specimen that is subjected to a load (force and / or torque) and / or displacement. Figure 1 is a simplified schematic diagram of an example of a test system 100 or portions thereof according to embodiments of the disclosure. The test system 100 generally includes a force sensor 102 (which can be a component of a load cell 104), an actuator 106, and one or more supports 108 for supporting a test specimen 110. The test specimen can be an automobile, a material, an elastomer, or any other physical test specimen.

[0021] The actuator 106 can include a hydraulic, pneumatic, or electric actuator, or another suitable actuator that can be used to apply a mechanical load 112 (e.g., torque, force, weight, tension, compression, or pressure) to the test specimen 110. The force sensor 102 includes one or more sensing elements (e.g., strain gauges coupled to a flexible element) that are configured to convert the applied mechanical force 112 into an electrical output signal 114 indicative of the applied mechanical force 112. The sensor 102 includes one or more sensing elements that generally generate the electrical output signal 114 based on a motion or displacement of an “active” or compliant portion 116 of the sensing element 117 relative to a fixed side 118 of the sensor 102 in response to the applied mechanical force 112.

[0022] In addition to controlling operation of the actuator 106, the controller 120 of the system 100 can be used to process the output signals 114 from the force sensor 102, the sensor signals 122 produced by the one or more sensors 124, and other information to determine a force measurement value, which can be indicated by a force measurement signal 126. Figure 2 is a schematic diagram of an example of a controller 120 in accordance with an embodiment of the present disclosure.

[0023] As shown in Figure 2 the controller 120 can include one or more processors 130 and a memory 132. The one or more processors 130 are configured to perform the various functions of the system 100 described herein, such as processing of signals (e.g., signals 114, 122, etc.), performing calculations, and other functions described herein, in response to executing instructions contained in the memory 132. The one or more processors 130 can be components of one or more computer-based systems, and can include one or more control circuits, microprocessor-based engine control systems, and / or one or more programmable hardware components, such as field programmable gate arrays (FPGAs).

[0024] The memory 132 is representative of local and / or remote memory or computer-readable media. Such memories include any conventional, patentable subject matter-enabled computer-readable media, and exclude transitory waves or signals. Examples of the memory 132 include conventional data storage devices, such as hard drives, read-only optical discs, optical storage devices, magnetic storage devices, and / or other suitable data storage devices.

[0025] The controller 120 can include circuitry 134 for use by the one or more processors 130 to receive inputs 136 (e.g., sensor signals 114, 122, etc.), issue control signals 138, and / or communicate data 140 (e.g., force measurement signal 126), such as in response to execution of instructions stored in the memory 132 by the one or more processors 130.

[0026] Figure 3is a schematic diagram of an example of a test system 100 in the form of an elastomer test system according to embodiments of the present disclosure. The elastomer test system 100 is configured to apply high speed and high force input motions to an elastomer material test specimen 110 in the form of generally high frequency (e.g., 100 hertz to over 1000 hertz) motion excitation using an actuator 106. In the example shown, the elastomer test system 100 includes a test frame 150 having a base support 152 and an upper support 154. The upper support 154 is supported by a column 156. The actuator 106 can be mounted in a crosshead 158 of the upper support 154 (as shown) or in the base support 152. The elastomer material test specimen 110 can be held by a support 108 including an upper clamp 160 and a lower clamp 162.

[0027] A load cell 104 including a force sensor 102 is positioned to receive as a mechanical input the force applied by the actuator 106 to the test specimen 110. In the example shown, the load cell 104 is located between the lower clamp 162 and the base support 152. However, the load cell 104 can also be located, for example, between the upper clamp 160 and the upper support 154. Figure 3

[0028] It will be appreciated that inertial errors in the force measurements produced by the sensor 102 (e.g., the signal 114 in Figure 1 ) are present due to motion of secondary masses in response to the input mechanical force. The secondary masses include, for example, the mass of the active sensor element portion 116, the mass of portions of the support 108 connected to or engaged with the active sensor element portion 116, and / or other masses that move with the active sensor element portion 116. Thus, in the elastomer tester example of Figure 2 , the secondary masses can include, for example, the active portion 116 of the sensor element 117 and the lower clamp 162.

[0029] Motion of the secondary masses, especially at higher frequencies (e.g., greater than 100 hertz), causes the secondary masses to experience vibrational accelerations. This causes inertial errors in the force sensor output signal 114 that are proportional to the secondary masses.

[0030] ​Such inertial errors can be compensated for in sensor force measurements by the controller 120 using a technique known as acceleration compensation, in which the acceleration of the secondary mass is estimated and used to compensate the force measurement value 114. The acceleration of the secondary mass can be estimated using one of the sensors 122, such as using an acceleration sensor that produces a sensor signal indicative of the acceleration of the secondary mass, or other suitable technique. Examples of acceleration compensation techniques are described in U.S. Patent Nos. 7,331,209, 9,658,122, and 10,551,286, which are incorporated by reference herein in their entireties.

[0031] Embodiments of the present disclosure aim to address an additional source of mechanical error in the force measurement values produced by the force sensor 102 in the test system 100. One such source of mechanical error is a mechanical damping error due to mechanical damping of the motion of the secondary mass of the system 100, such as viscous damping, Coulomb or dry friction damping, solid or structural damping, material or hysteresis damping, and / or sliding or interface damping. It has been a conventional view that the effect of such mechanical damping error in sensor force measurements in the test system 100 can be negligible. Accordingly, conventional techniques for processing sensor force measurements in the test system 100 have neglected such mechanical damping error and focused on providing acceleration compensation to the force measurement values.

[0032] Embodiments of the present disclosure stem from a finding that the above-mentioned mechanical damping error in the test system 100 due to motion of the secondary mass can in fact have a significant adverse effect on the accuracy of the force measurement values 114. Accordingly, one embodiment of the present disclosure aims to compensate the force measurement values 114 of the force sensor 102 for such mechanical damping to improve the accuracy of the force measurement values 114.

[0033] Figure 4 is an example model of the test system 100 according to embodiments of the present disclosure Figure 1 and Figure 3 is a simplified free-body diagram of the example model of the test system 100. The illustrated model includes the test specimen 110, the mass (m sensor ) of the active portion 116 of the sensing element of the force sensor 102, and possibly the mass (m support ) of the support 108 that supports or connects to the test specimen 110, which is located on the active or movable side of the force sensor 102 or load cell 104. The mass of the active portion 116 of the sensing element 117 can include, for example, the mass of a metal beam that deflects in response to an applied force. Strain gauges attached to the beam measure the deflection and the sensor 102 produces a force measurement value output 114 based on the deflection.

[0034] The illustrated masses can constitute the above-discussed secondary mass m (e.g., m = m sensor + m support), which corresponds to components of the system 100 that move (e.g., vibrate) in response to the actuator 106 applying the applied force 112 to the test sample 110 during a test operation.

[0035] The active or deflected portion 116 (e.g., beam) of the sensing element 117 of the force sensor 102 is represented in the model by a spring 166 with a stiffness k, and the damping characteristics of the sensor 102, as well as other components in the system 100 that can affect the force measurements of the sensor 102 (e.g., the support 108) are represented by a damping b.

[0036] The sum of forces around the secondary mass m is shown in Equation 1.

[0037] Equation 1 Where: F a = applied dynamic force k = stiffness of the sensor b = damping constant of the sensor m = secondary mass = m sensor + m support x = displacement in the x direction = velocity in the x direction = acceleration in the x direction Thus, the sum of forces around the secondary mass m is equal to the secondary mass m times its acceleration (inertial error due to secondary mass), which is equal to the velocity of the mass m in the -x direction times the damping of the sensor (error due to mechanical damping), plus the displacement of the mass m in the -x direction times the stiffness of the sensor (measured dynamic force ( F meas = kx), plus any applied force from the actuator (Fa).

[0038] Thus, Equation 1 can be rearranged to get Equation 2.

[0039] Equation 2 The inertial error (-m ) can be compensated for by acceleration compensation by establishing an estimate of the acceleration of the secondary mass ( ) (e.g., from an acceleration sensor 124 ( Figure 1 ) and the secondary mass ( the estimated inertial error (e )( )) to calculate a corrected dynamic force (F corr ), as shown in equation 3.

[0040] Equation 3 Combining equation 2 and equation 3, equation 4 can be derived.

[0041] Equation 4 The inertial error (e ) is offset by the estimated inertial error (e )( )) to yield equation 5.

[0042] Equation 5 Thus, the error remaining in equation 5 is the mechanical damping error (e ) of the system. Embodiments of the present disclosure are directed to applying a mechanical damping compensation to equation 5 to eliminate this mechanical damping error. In one embodiment, this is accomplished by multiplying an estimate of the damping (e ) by an estimate of the velocity (e ) to calculate an estimate of the mechanical damping error. Applying the mechanical damping compensation to equation 5 yields equation 6.

[0043] Equation 6 Thus, controller 120 can compensate the measured force indicated by signal 114 to produce a corrected force measurement that more accurately matches applied force 112.

[0044] As noted above, conventional techniques for processing force measurements in a test system assume that the mechanical damping error is inconsequential. However, it has now been discovered that this is not the case. For example, when actuator 106 of test machine 100 vibrates a test specimen at a high frequency (e.g., greater than 100 Hz) or at the resonant frequency of the active portion 116 of the sensing element 117, the mechanical damping error can have a significant impact on the accuracy of the force measurement produced by the sensor and cause the force measurement to deviate by as much as 25%. In fact, at times, the mechanical damping error can exceed the inertial error of system 100.

[0045] Accordingly, embodiments of the present disclosure provide the above-described mechanical damping compensation for compensating the load measurement 114 of test system 100 to improve the accuracy of force and / or torque measurements. Embodiments of the present disclosure are also directed to specific techniques for implementing this mechanical damping compensation in test system 100.

[0046] Mechanical damping compensation can be performed substantially in real time using controller 120, wherein processing of the force sensor output 114 includes applying mechanical damping compensation (whether or not conventional acceleration compensation is used) to generate a torque output by the force sensor. Figure 1 Signal 126 in the diagram represents the corrected force measurement value. Alternatively, mechanical damping compensation and acceleration compensation can be applied after force measurement test data is acquired from force sensor 102. Here, controller 120 may represent a processor and circuitry external to system 100.

[0047] Examples of mechanical damping compensation include estimating the damping constant (~ ) and the estimated rate of secondary mass (~ In some embodiments, the damping constant is estimated based on the material properties of the active portion 116 of the sensing element 117.

[0048] When the mechanical damping to be addressed is viscous damping or dry friction damping, the damping constant can be directly measured experimentally on the system. In one example, damping error and inertial error can be measured by applying a known sample force (possibly a zero sample force) and obtaining the resulting force measured by sensor 102. The force measurement error due to inertial (acceleration) effects and the force measurement error due to damping (velocity) effects can be decomposed because the inertial effect is proportional to acceleration (e.g., measured by acceleration sensor 124), and the damping effect is proportional to velocity (measured or estimated). If the applied sample force is sinusoidal, both components can be extracted from the measurement error because for a sinusoidal signal, the acceleration and velocity have a 90-degree phase difference.

[0049] The estimation of this damping constant does not have to be limited to a single scalar value. Instead, the damping effect can be included as a frequency domain transfer function or its equivalent digital filter, and its effect can be combined with acceleration effects and incorporated as a more generalized sensor impedance transfer function.

[0050] Speed ​​estimation (~ This can be performed based on measurements from one or more sensors 124 of system 100. For example, when sensor 124 of system 100 ( Figure 1 When sensor 124 includes a displacement sensor configured to measure the displacement of secondary mass (e.g., active part 116) along the x-axis, the derivative of displacement sensor output 122 can be used to estimate velocity. When sensor 124 includes an accelerometer that measures the acceleration of secondary mass (e.g., conventionally used to provide acceleration compensation), the integral of accelerometer output 122 can be used to estimate velocity.

[0051] In one embodiment, the velocity estimate is performed via a pair of complementary filters (similar to crossover filters used in audio speakers) or using, for example, a Kalman filter, by combining the derivative of the displacement sensor output 122 with the integral of the acceleration sensor output 122. In most applications, this combined measurement for estimating velocity can be the preferred approach.

[0052] The sensors 124 of the system 100 can also include a velocity sensor (e.g., a rate gyroscope or a linear velocity sensor, or an encoder velocity signal) configured to measure the velocity of the secondary mass along the x-direction. Here, the output 122 from the velocity sensor can be used as the velocity estimate.

[0053] There can be a phase shift and / or amplitude attenuation or amplification between the force sensor output signal 114 and the damping compensation, due to, for example, communication between the force sensor output 114 and the signals 122 from one or more sensors 124 used to estimate the damping error (e.g., the velocity estimate), and processing performed by the controller 120. For example, different regulators, filters, samplers, etc. can introduce delays or different delays, which can result in some phase shift and / or amplitude attenuation or amplification, and these delays can vary with frequency.

[0054] In one aspect of the disclosure, the controller 120 can process this phase shift and / or amplitude attenuation or amplification between the force measurement output 114 of the sensor 102 and the mechanical damping compensation before generating the final force measurement output 126 including the mechanical damping compensation. Similarly, the controller 120 can also process the phase shift and / or amplitude attenuation or amplification between the force sensor output 114 and the acceleration compensation before generating the final force measurement output 126. Alternatively, this phase shift and / or amplitude compensation can be performed by the controller 120 or another processing system after testing.

[0055] In some test systems, Figure 1 The illustrated supports 108 can include parallel supports that create additional forms of mechanical damping in parallel with the force measurement sensing element 117 of the sensor 102. This is shown in Figure 5 A simplified schematic of an example test system 100 is provided. The test system 100 generally includes Figure 1The test system 100 includes components and a parallel support 170, which is connected in parallel with the sensing element 117 between the test sample 110 and a ground terminal 172, representing a common physical connection. The connection between the parallel support 170 and the ground terminal or common connection 172 can be achieved via a connector 174, which allows the parallel support 170 to perform linear or rotational movement relative to the ground terminal. The connector 174 may include translational or linear bearings, rotary bearings, etc. The motion provided by the connector 174... Figure 1 The system introduces additional mechanical damping, which diverts a portion of the applied force 112 from the actuator 106 away from the sensor sensing element 117, resulting in a mechanical damping error (hereinafter referred to as "parallel mechanical damping error") in the force sensor measurement indicated by the output signal 114.

[0056] A work condition simulator is possible to present Figure 1 , Figure 4 and Figure 5 The diagram illustrates one type of test system 100. A performance simulator utilizes actuator 106 to generate mechanical inputs 112 (e.g., force, motion, etc.) representing a specific performance condition applied to a test sample 110. Examples of such simulators include automotive driving performance simulators, such as kinematic and compliance systems, spindle-coupled road simulators, and other systems manufactured by MTS Corporation. Such systems or simulators rely on force sensors 102 for force measurements to quantify the mechanical inputs 112 and the test conditions generated by actuator 106. Various aspects of such performance simulators can be referred to in conjunction with the above description. Figure 1 and Figure 4 Modeling is then performed. Therefore, the mechanical damping compensation embodiment described above can be applied to force measurements generated by certain force sensors in a work condition simulator to improve the accuracy of the force measurements.

[0057] In addition, certain aspects of the work condition simulator may present Figure 5 The arrangement shown. For example, Figure 6is an isometric view of a vehicle restraint system 180 of a full vehicle driving mode simulator 100 according to embodiments of the present disclosure. The restraint system 180 is one of a pair of systems in which a first restraint system is arranged on one side of the vehicle and a second restraint system is arranged on the other side. The restraint system 180 includes a plate 182 that forms part of the support 108 of the system 100 and is configured to be mounted to the frame of the vehicle so as to provide support through the center of gravity of the vehicle under test (test specimen 110). This manner of attachment constrains certain degrees of freedom of the test vehicle, such as motion in the longitudinal or travel direction of the vehicle (x-axis), motion in the lateral direction of the vehicle (y-axis), and rotation of the vehicle about the vertical axis (z-axis), while allowing the vehicle to pitch (rotate about the y-axis), roll (rotate about the x-axis), and lift along the z-axis. Specifically, a pivot 184 accommodates vehicle roll, while an arm 186 and associated joints accommodate vehicle pitch and vehicle lift along the z-axis, while providing constraints on the other degrees of freedom.

[0058] The restraint system 180 includes a plurality of load cells, such as load cell 104A (e.g., a bi-directional load cell) connected to the plate 182 or test specimen support 108, and load cells 104B (one shown) connected in series with linear actuators 106, respectively. Each load cell 104 includes one or more force sensors. The load cell 104A is also connected to a vertical support 188 through a joint 174 formed by a linear bearing 190 configured to slide along a rail 192 oriented in the z-axis to accommodate vehicle motion along the z-axis. The load cells 104B are also connected to the arm 186 through joints 174 formed by the hinges 184 and ultimately to a common location or ground shared with the vertical support 188.

[0059] The load cells 104B are connected between the actuators 106 and one of the arms 186, respectively. The actuators 106 link the arms 186 through a parallel linkage in the x-z plane, causing the assembly including the plate 182 and the load cell 104A to lift along the z-axis. This motion is guided by the linear bearing 190 sliding on the rail 192.

[0060] Motion of the linear bearing 190 along the rail 192 generates damping forces that are shunted away from the load cells 104B through the parallel support and joints 174 (e.g., vertical support 188, arm 186), as Figure 5 is generally shown. Thus, the force measurements generated by any one of the load cells 104B do not accurately reflect the load applied to the specimen under test by the corresponding actuator 106.

[0061] Figure 7 is a test system 100 according to embodiments of the present disclosure Figure 5 and Figure 6A simplified free-body diagram of an example model of aspects of the illustrated constraint system 180. With Figure 4 the model similar to that of FIG. 6, Figure 7 the model includes the mass (m sensor ) of the active portion 116 of the sensing element 117 of the force sensor 102, and possibly the mass (m support ) of the support 108 that supports or is attached to the test sample 110 and is on the active or movable side of the force sensor 102 or load cell 104. In addition, the active or movable portion 116 (e.g., beam) of the sensing element 117 of the force sensor 102 is represented in the model by a spring 166 having a stiffness k, and the damping of the sensor and components associated with the secondary mass and in parallel with the sensor 102 is represented by a damping b, as discussed above in connection with Figure 3

[0062] Figure 7 the mass (m parallel ) of the parallel support 170 is also included in the model. The parallel mechanical damping associated with the parallel support 170 is represented by a damping constant b', which acts to shunt a portion of the applied force 112 from the actuator 106 away from the active sensing element portion 116. Thus, the summation of forces in equation 1 around the secondary mass m is modified as indicated in equation 7 to include the parallel mechanical damping (b' ) caused by the parallel support, where represents the velocity (linear or rotational) of the parallel support experiencing the damping b'.

[0063] Equation 7 The mechanical damping compensation and the acceleration compensation can be applied by the controller 120 to equation 7 as described above to compensate for inertia and damping errors. After applying these compensations, only the parallel damping error remains in equation 7.

[0064] In one embodiment, the problem of parallel mechanical damping error is addressed by applying a parallel mechanical damping compensation based on an estimated value of the damping associated with the parallel support 170 and an estimated value of the velocity to calculate an estimated value of the parallel mechanical damping error . The estimated value of the damping and the estimated value of the velocity may be obtained using any of the techniques described above. For example, the estimated velocity may be obtained using the acceleration, displacement, and / or velocity sensors 124 as discussed above with respect to the velocity of the secondary mass.

[0065] Applying the parallel mechanical damping compensation to equation 7 results in a corrected dynamic force (F corr ​) or a corrected force measurement that is approximately equal to the applied force, as shown in equation 8.

[0066] Equation 8 Accordingly, applying parallel mechanical damping compensation to the sensor force measurements in the test system 100 by the controller 120 can be used to improve the accuracy of the force measurements 126 output by the controller 120. Figures 5-7

[0067] Accordingly, some embodiments of the present disclosure include a test system 100 comprising Figure 5 and Figure 6 components of the test system 100, wherein the controller 120 is configured to apply parallel mechanical damping compensation to the force measurements generated by the force sensor 102 to generate a corrected force measurement 126 that more accurately reflects the applied force 112. The controller 120 can be further configured to apply additional compensation to the force measurements, such as the acceleration compensation, damping compensation, phase offset compensation, and / or amplitude compensation described above, to further correct the force measurements.

[0068] While embodiments of the present disclosure have been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and details can be made therein without departing from the spirit and scope of the disclosure.​

Claims

1. A test system comprising: a force sensor configured to generate a force output indicative of a force applied to the force sensor, the force sensor having an active side and a fixed side; a support connected to the force sensor and configured to support a test sample; a sensor configured to generate a sensor output indicative of a velocity of the active side of the force sensor relative to the fixed side; and a controller configured to: receive the force output and the sensor output; compute a damping compensation based on the sensor output, a damping constant estimate associated with a damping characteristic of the force sensor and the support, and a secondary mass comprising a mass of the force sensor and the support; and generate a corrected force measurement based on the force output and the damping compensation.

2. The test system of claim 1, wherein: the force sensor is connected between the support and a common location; the support comprises a parallel support and a joint, the parallel support and the joint being connected in parallel between the force sensor and the common location; the controller is configured to compute a parallel damping compensation based on a parallel damping constant estimate associated with the joint and a velocity estimate of the parallel support; and the corrected force measurement is based on the parallel damping compensation.

3. The test system of claim 2, wherein the joint comprises a translational bearing or a rotational bearing.

4. The test system of any preceding claim, wherein: the controller is configured to compute an acceleration compensation based on the sensor output and the secondary mass; and the corrected force measurement is further based on the acceleration compensation.

5. The test system of any preceding claim, wherein the sensor is selected from the group consisting of: a displacement sensor, a velocity sensor, and an acceleration sensor.

6. The test system of any preceding claim, wherein the support comprises a clamp for holding an elastomeric material test sample.

7. The test system of any preceding claim, wherein the controller is configured to apply the damping compensation to the force output within a predetermined frequency range in which the force sensor is subject to vibrations.

8. A method of correcting a force measurement in a test system, the method comprising: supporting a test sample in a support connected to a force sensor; generating, using the force sensor, a force output indicative of a force applied to the force sensor; generating a sensor output indicative of a velocity of an active side of the force sensor relative to a fixed side of the force sensor; receiving, by a controller, the force output and the sensor output; computing, using the controller, a damping compensation based on the sensor output, a damping constant estimate associated with a damping characteristic of the force sensor and the support, and a secondary mass comprising a mass of the force sensor and the support; and generating, using the controller, a corrected force measurement based on the force output and the damping compensation. ​ ​ 9. The method of claim 8, wherein: the force sensor is connected between the support and a common location; the support includes a parallel support and a joint, the parallel support and the joint being connected in parallel between the force sensor and the common location; the method includes using the controller to compute a parallel damping compensation based on a parallel damping constant estimate associated with the joint and a velocity estimate of the parallel support; and the corrected force measurement is based on the parallel damping compensation.

10. The method of claim 9, wherein the joint includes a translational bearing or a rotational bearing.

11. The method of claim 9, wherein: the method includes using the controller to compute an acceleration compensation based on the sensor output and the secondary mass; and the corrected force measurement is further based on the acceleration compensation.

12. The method of any of claims 1-11, wherein the sensor is selected from the group consisting of: a displacement sensor, a velocity sensor, and an acceleration sensor.

13. The method of any of claims 1-12, wherein the support includes a clamp for holding an elastomeric material test specimen.

14. The method of any of claims 1-12, including applying the damping compensation to the force output over a predetermined frequency range in which the force sensor is subject to vibration.

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