Apparatus and method for calibrating a shear test tool

Abstract

An apparatus for calibrating a shear testing tool utilizes a resilient pivot mechanism to improve the accuracy and reliability of force calibration. The apparatus includes a fixed element, a pivotable element configured to be rotatable relative to the fixed element, and a resilient pivot mechanism coupled between the fixed element and the pivotable element to form a pivot. When a force is applied on the pivotable element by the shear testing tool in order to rotate the pivotable element and lift a weight coupled to the pivotable element, the pivotable element is rotatable about the pivot to lift the weight.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to shear testing of interconnect bonds formed on electronic devices, such as wire bonds formed on electronic devices, or die bonds formed between a die and a substrate, and more particularly to calibrating a shear testing tool for such bond joints. BACKGROUND

[0002] During semiconductor assembly and packaging, shear testing can be performed to determine the bond strength of interconnect bonds or the degree of attachment between a die and a substrate. It is important to test the mechanical strength of these interconnect bonds in electronic devices in order to accurately assess the quality of these bonds, and thus determine whether the bond strength is sufficient and / or whether bond parameters need to be modified.

[0003] In order to accurately measure the bond strength using a shear testing tool, it is necessary to periodically calibrate the shear testing tool in order to compensate and / or correct the shear testing tool when test results show any variation and deviation from a predetermined allowable tolerance. In prior art force calibration devices for shear testing tools, a bearing pivot is typically used to form a pivot between a fixed element and a pivotable element for calibration. In such a force calibration process, bearing friction in the mechanical bearing can cause the bearing to wear and tear, thereby reducing the service life of the bearing and the reliability of the force calibration. In turn, the calibration results determined using the conventional force calibration device can not be accurate because the bearing friction is not constant and can vary due to the use of different weights in the calibration process. Furthermore, the bearing components can rust and corrode over time if they contain iron. Although lubricants can be used to reduce friction and rust, this results in more maintenance work and higher costs.

[0004] Accordingly, it would be beneficial to design a new force calibration device for a shear testing tool that can avoid at least some of the above-mentioned drawbacks faced by conventional force calibration devices. SUMMARY

[0005] Accordingly, it is an object of the present invention to seek to provide an improved force calibration apparatus that utilizes a resilient pivot mechanism to improve the service life and reliability of the force calibration apparatus.

[0006] According to a first aspect of the present invention, there is provided an apparatus for calibrating a shear testing tool. The apparatus comprises: a fixed element; a pivotable element configured to be rotatable relative to the fixed element; and a resilient pivot mechanism coupled between the fixed element and the pivotable element to form a pivot, such that when a force is applied on the pivotable element by the shear testing tool in order to rotate the pivotable element and lift a weight coupled to the pivotable element, the pivotable element is able to rotate about the pivot to lift the weight.

[0007] In the apparatus for calibrating a shear testing tool, an elastic pivot mechanism is used instead of a bearing pivot used in the prior art force calibration device. Therefore, no friction occurs between the elastic pivot mechanism and other components of the force calibration device. As a result, the problems caused by bearing friction in the prior art force calibration device can be avoided accordingly. The service life and reliability of the force calibration device will be significantly improved, and the calibration results will be more accurate even after being used for a period of time. In addition, no lubricant is needed to reduce friction and rust, so maintenance work and costs will be reduced.

[0008] In some embodiments, the pivotable element can define a first length in a horizontal direction and a second length in a vertical direction relative to the pivot, the weight is coupled to an end of the first length distal from the pivot, and the shear testing tool is operable to exert a substantially horizontal force on an end of the second length distal from the pivot to rotate the pivotable element and lift the weight.

[0009] In one embodiment, the elastic pivot mechanism comprises a cross spring pivot mechanism. The cross spring pivot mechanism is formed by a first spring leaf having an opening and a second spring leaf sized to pass through the opening of the first spring leaf, the first and second spring leaves being arranged at an angle to each other. Each of the first and second spring leaves has a first edge fixed to the fixed element and a second edge fixed to the pivotable element, such that each of the first and second spring leaves is deflectably in contact with the fixed element and the pivotable element. Preferably, the first and second spring leaves are mounted perpendicular to each other.

[0010] In another embodiment, the elastic pivot mechanism comprises a first pair of spring leaves and a second pair of spring leaves. The fixed element has opposite first and second sides positioned along an interface between the fixed element and the pivotable element. The first pair of spring leaves is mounted on the first side of the fixed element, while the second pair of spring leaves is mounted on the second side of the fixed element. Each spring leaf is deflectably in contact with the fixed element and the pivotable element. Preferably, the spring leaves in the first pair are mounted perpendicular to each other, and the spring leaves in the second pair are also mounted perpendicular to each other.

[0011] In some embodiments, the apparatus can further comprise a coupling device configured to detachably couple the weight to the pivotable element. In one embodiment, the coupling device can comprise a hook, the weight being configured to be hung on the hook.

[0012] In some embodiments, the shear testing tool can comprise a shear testing rod and a force sensor coupled to the shear testing rod. The force sensor is operable to measure a force exerted by the shear testing rod on the pivotable element in order to rotate the pivotable element and lift the weight. In one embodiment, the shear testing rod can have a tapered tip.

[0013] In some embodiments, the apparatus can further include a processor operably connected to the force sensor. The processor is configured to determine a relatively constant force measured with the force sensor after the weight has been lifted from a rest position by the force applied by the shear test rod.

[0014] According to a second aspect of the present application, there is provided a method for calibrating a shear test tool. The method comprises: providing a calibration apparatus comprising a fixed element, a pivotable element configured to be rotatable relative to the fixed element, and an elastic pivot mechanism coupled between the fixed element and the pivotable element to form a pivot axis such that the pivotable element is rotatable about the pivot axis; and applying a force on the pivotable element using the shear test tool such that the pivotable element is rotated about the pivot axis to lift a weight coupled to the pivotable element.

[0015] In some embodiments, the pivotable element defines a first length in a horizontal direction and a second length in a vertical direction relative to the pivot axis. Accordingly, the method further comprises: coupling the weight to an end of the first length distal to the pivot axis; and wherein the step of applying a force on the pivotable element comprises applying a substantially horizontal force on an end of the second length distal to the pivot axis with the shear test tool to rotate the pivotable element and lift the weight.

[0016] In one embodiment, the elastic pivot mechanism comprises a cross-spring pivot mechanism. The cross-spring pivot mechanism can be formed by a first spring leaf having an opening and a second spring leaf sized to pass through the opening of the first spring leaf, the first and second spring leaves being arranged at an angle to each other. Preferably, the first and second spring leaves are mounted perpendicular to each other.

[0017] In another embodiment, the elastic pivot mechanism comprises a first pair of spring leaves and a second pair of spring leaves. The fixed element has opposing first and second sides positioned along an interface between the fixed element and the pivotable element. The first pair of spring leaves is mounted on the first side of the fixed element, while the second pair of spring leaves is mounted on the second side of the fixed element. Each spring leaf is deflectably in contact with the fixed element and the pivotable element. Preferably, the spring leaves in the first pair are mounted perpendicular to each other, and the spring leaves in the second pair are mounted perpendicular to each other.

[0018] In some embodiments, the shear test tool can comprise a shear test rod and a force sensor coupled to the shear test rod. The method further comprises: moving the shear test rod to apply a force on the pivotable element; and measuring, with the force sensor, the force applied to the pivotable element with the shear test rod to rotate the pivotable element and lift the weight.

[0019] In some embodiments, the method can further comprise determining, with the processor or computer system, a relatively constant force measured with the force sensor after the weight has been lifted from the rest position by the force exerted on the pivotable element by the shear test rod.

[0020] These and other features, aspects, and advantages will become better understood with respect to the following description, parts of which are described in the description of the section entitled "DETAILED DESCRIPTION", the appended claims, and the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0021] Embodiments of the present application will now be described, by way of example only, with reference to the accompanying drawings in which:

[0022] Figure 1A is a cross-sectional view of an apparatus for calibrating a shear test tool according to some embodiments of the present application.

[0023] Figure 1B is Figure 1A is a cross-sectional view of the apparatus shown, wherein the fixed element and the pivotable element of the apparatus have been separated.

[0024] Figure 2A and Figure 2B show a front view and an isometric view, respectively, of a resilient pivot mechanism according to a first embodiment of the present application.

[0025] Figure 2C is a perspective view of an apparatus for calibrating a shear test tool according to a first embodiment of the present application.

[0026] Figure 3A shows a resilient pivot mechanism comprising two pairs of spring leaves according to a second embodiment of the present application.

[0027] Figure 3B and Figure 3C show a respective perspective view and a front view of an apparatus for calibrating a shear test tool according to a second embodiment of the present application.

[0028] Figure 4 is a cross-sectional view of an apparatus for calibrating a shear test tool according to an embodiment of the present application when used for calibrating a shear test tool.

[0029] Figure 5 is a line graph showing calibration results of a shear test tool obtained using an apparatus for calibrating a shear test tool according to a first embodiment of the present application.

[0030] Figure 6 is a flowchart illustrating a method for calibrating a shear test tool according to an embodiment of the present application.

[0031] In the drawings, like reference numerals refer to like parts throughout the various views. DETAILED DESCRIPTION

[0032] Figure 1A is a cross-sectional view of an apparatus 100 for calibrating a shear testing tool according to some embodiments of the present application. As shown, the apparatus 100 includes a fixed element 111, a pivotable element 112, and a resilient pivot mechanism 113. The pivotable element 112 is configured to be rotatable relative to the fixed element 111. Figure 1A Figure 1B is a cross-sectional view of the apparatus 100, wherein the fixed element 111 and the pivotable element 112 of the apparatus have been separated. The resilient pivot mechanism 113 is coupled between the fixed element 111 and the pivotable element 112 to form a pivot, such that upon application of a horizontally oriented force by the shear testing tool to the pivotable element 112 in order to rotate the pivotable element 112 and lift a weight coupled to the pivotable element 112, the pivotable element 112 is rotatable about the pivot to lift the weight.

[0033] Figure 2A and Figure 2B respectively show a front view and an isometric view of the resilient pivot mechanism 113 according to a first embodiment of the present application. Figure 2C is a perspective view of the apparatus 100 according to the first embodiment of the present application. In this embodiment, the resilient pivot mechanism 113 includes a cross-spring pivot mechanism formed by a first spring leaf 113a having an opening and a second spring leaf 113b sized to pass through the opening of the first spring leaf 113a. When the first spring leaf 113a and the second spring leaf 113b are installed between the fixed element 111 and the pivotable element 112, the first spring leaf 113a and the second spring leaf 113b are installed perpendicular to each other, as shown in Figure 2C

[0034] In this embodiment, the first spring leaf 113a is coupled between the fixed element 111 and the pivotable element 112 by a first coupling device including four pairs of bolts and nuts, while the second spring leaf 113b is coupled between the fixed element 111 and the pivotable element 112 by a second coupling device including two pairs of bolts and nuts. Referring to Figures 2A to 2C ​​The first spring leaf 113a has a first edge 113a-1 fixed to the fixed element 111 and a second edge 113a-2 fixed to the pivotable element 112, such that the first spring leaf 113a is in deflectable contact with both the fixed element 111 and the pivotable element 112. Similarly, the second spring leaf 113b has a first edge 113b-1 fixed to the fixed element 111 and a second edge 113b-2 fixed to the pivotable element 112, such that the second spring leaf 113b is in deflectable contact with both the fixed element 111 and the pivotable element 112. It should be noted that the first coupling means and / or the second coupling means in the present embodiment are for illustration only. In other embodiments, different coupling means can be used to mount the first spring leaf 113a and the second spring leaf 113b between the fixed element 111 and the pivotable element 112.

[0035] It should be understood that the components and structure of the cross spring pivot mechanism in the present embodiment are for illustration only. The cross spring pivot mechanism can have different structure and components, for example, the cross spring pivot mechanism can be a one-piece component having two spring leaves that are integral and arranged perpendicularly with respect to each other.

[0036] In a second embodiment of the present application, the resilient pivot mechanism 113 comprises a first pair of spring leaves 113A and a second pair of spring leaves 113B. Figure 3A Two pairs of spring leaves 113A and 113B according to the second embodiment of the present application are shown. Each pair of spring leaves comprises two spring leaves mounted perpendicularly with respect to each other between the fixed element 111 and the pivotable element 112. As Figure 3A shown, the first pair of spring leaves 113A comprises a first spring leaf 113A-1 and a second spring leaf 113A-2, and the second pair of spring leaves 113B comprises a first spring leaf 113B-1 and a second spring leaf 113B-2. Figure 3B and Figure 3C Perspective and front views of the apparatus 100 according to the second embodiment of the present application are shown, respectively. As Figure 3B and Figure 3C shown, the fixed element 111 has opposite first and second sides 111a and 111b located on the interface between the fixed element 111 and the pivotable element 112. The first pair of spring leaves 113A is mounted on the first side 111a of the fixed element 111, while the second pair of spring leaves 113B is mounted on the second side 111b of the fixed element 111. Each spring leaf is in deflectable contact with both the fixed element 111 and the pivotable element 112. The two spring leaves 113A-1 and 113A-2 are mounted perpendicularly with respect to each other, and the two spring leaves 113B-1 and 113B-2 are also mounted perpendicularly with respect to each other.

[0037] Figure 4is a cross-sectional view of the apparatus 100 for calibrating a shear testing tool 115 according to an embodiment of the present application. In use, a weight 114 having a predetermined weight value (e.g. constant weight or dead mass) is coupled to the pivotable element 112 by a coupling means. In this embodiment, the coupling means comprises a hook 116, the weight 114 being configured to hang from the hook 116. It is noted that the weight 114 can be coupled to the pivotable element 112 in any way using any of the other embodiments of the present application, as long as the weight 114 exerts a known vertically oriented force Fl on the pivotable element 112. For example, the weight 114 can be attached directly to the bottom / top surface of the pivotable element 112, with or without any additional coupling means.

[0038] The shear testing tool 115 comprises a shear testing rod 115a and a force sensor 115b coupled to the shear testing rod 115a. The shear testing tool 115 is moved so that the shear testing rod 115a comes into contact with the pivotable element 112 and exerts a force on the pivotable element 112 to rotate the pivotable element 112 in order to lift the weight 114. The force sensor 115b is operable to measure the reaction force exerted by the pivotable element 112 on the shear testing rod 115a as the shear testing rod 115a rotates the pivotable element 112 to lift the weight 114. The shear testing rod 115a can have a tapered tip to minimize contact between the shear testing rod 115a and the surface on which the interconnecting joint is formed or positioned.

[0039] As shown in Figure 4 In this embodiment, the pivotable element 112 defines a first length LI along a horizontal direction relative to the pivot axis and a second length L2 along a vertical direction relative to the pivot axis. The weight 114 is coupled to an end of the first length LI distal to the pivot axis and the shear testing tool 115 is operable to exert a substantially horizontal force F2 on an end of the second length L2 distal to the pivot axis to rotate the pivotable element 112 in order to lift the weight 114. In this embodiment, the end of the first length LI distal to the pivot axis is located at an end P of the arm of the pivotable element 112. However, in other embodiments, the location of the end of the first length LI distal to the pivot axis can be different, for example, the location can be positioned at a point other than at the end P.

[0040] In some embodiments of the present application, the apparatus 100 can further comprise a processor or any computing system operatively connected to the force sensor 115b and configured to determine a relatively constant force measured by using the force sensor 115b after the weight 114 has been lifted from its rest position by the force exerted on the pivotable element 112 by the shear testing rod 115a.

[0041] Figure 5is a line graph showing the calibration result of the shear testing tool 115 obtained using the apparatus 100 according to the first embodiment of the present application. As shown in Figure 5 the reaction force measured by the force sensor 115b increases significantly as the shear testing rod 115a moves along the horizontal direction towards the pivotable element 112 until the pivotable element 112 starts to rotate and the weight 114 is lifted. Once the processor determines that the force measured by the force sensor 115b remains relatively constant, i.e. the force measured by the force sensor 115b does not increase significantly as the shear testing rod 115a moves further along the horizontal direction, the value of the relatively constant force C is taken as the calibration result for calibrating the shear testing tool 115. It is noted that the force measured by the force sensor 115b, although can not increase significantly after the weight 114 is lifted, can not become a truly constant value during the calibration process. The reason is that in order to ensure that the shear testing rod 115a moves along the horizontal direction at a constant speed, the force applied to the pivotable element 112 will still increase slowly as the shear testing rod 115a moves further, because the pivot spring force will increase as the spring leaf of the elastic pivot mechanism 113 deforms further. Since the spring constant of the elastic pivot mechanism 113 is a very small value, e.g. 0.017 g / um, the increase in the measured force caused by the further deformation of the elastic pivot mechanism 113 is not significant.

[0042] In order to calibrate the shear testing tool 115 accurately, a plurality of weights with different values can be used to calibrate the shear testing tool 115.

[0043] Figure 6 is a flow chart illustrating a method 600 of calibrating a shear testing tool using the apparatus 100 according to an embodiment of the present application.

[0044] In step 601, a calibration apparatus 100 is provided, which comprises a fixed element 111, a pivotable element 112 configured to be rotatable relative to the fixed element 111, and an elastic pivot mechanism 113 coupled between the fixed element 111 and the pivotable element 112.

[0045] In step 602, a weight 114 with a predetermined value is coupled to the pivotable element 112.

[0046] In step 603, a shear testing tool 115 is moved relative to the pivotable element 112 such that a shear testing rod 115a of the shear testing tool 115 contacts the pivotable element 112 and exerts a force to rotate the pivotable element 112 and lift the weight 114.

[0047] In the present embodiment, the shearing test tool 115 can be first moved downward until the shearing test bar 115a is at a predetermined height, and then the shearing test tool 115 is moved in a horizontal direction at a constant speed until the shearing test bar 115a contacts the pivotable element 112 at a predetermined position, for example, at an end of the second length L2 away from the pivot defined by the pivotable element 112. Once the shearing test bar 115a contacts the pivotable element 112, a substantially horizontal force is applied on the pivotable element 112 to rotate the pivotable element 112 and lift the weight 114.

[0048] In step 604, the processor or computing system operatively connected to the shearing test tool 115 determines a relatively constant force measured by the force sensor 115b of the shearing test tool 115 after the weight 114 has been lifted by the force applied on the pivotable element 112 by the shearing test bar 115a.

[0049] In particular, during the movement of the shearing test bar 115a in the horizontal direction, the processor or computing system can record the force measured by the force sensor 115b as the distance of the movement of the shearing test bar 115a in the horizontal direction increases. The value of the relatively constant force is determined based on the recorded forces.

[0050] To accurately calibrate the shearing test tool 115, steps 602 to 604 can be performed using a plurality of weights with different weight values.

[0051] From the above description, it can be appreciated that the apparatus and method for calibrating a shearing test tool provided by the embodiments of the present application utilize an elastic pivot mechanism to form a pivot between a fixed element and a pivotable element, such that when a force is applied on the pivotable element by the shearing test tool, the pivotable element rotates around the pivot to lift a weight. Compared to the force calibration device of the prior art formed by a bearing pivot, since the elastic pivot mechanism installed between the fixed element and the pivotable element does not generate friction, problems caused by bearing friction in various mechanical bearings will be avoided. In particular, the service life and reliability of the force calibration device will be significantly improved, since lubricants are not required to reduce friction and rust, thus reducing the maintenance work and cost of the force calibration device. Furthermore, more accurate calibration results will be obtained, especially in the case of long-term use, since inaccuracy caused by bearing friction is avoided.

[0052] Table 1 below illustrates the calibration results obtained using the apparatus 100 according to the first embodiment of the present application. Weights with different values are used to perform the calibration process. As can be seen from the results shown in Table 1, the force ratios obtained from the apparatus 100 based on the measurement results are relatively constant.

[0053] Table 1

[0054] Weight (g) Force (N / g) Ratio 5.000 8.600 1.7201 10.000 17.210 1.7210 25.000 43.084 1.7234 50.000 86.259 1.7252 100.000 172.523 1.7253

[0055] While the application has been described in detail with reference to certain implementations thereof, other implementations are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the implementations contained herein.

Claims

1. An apparatus for calibrating a shear testing tool, the apparatus comprising: a fixed element; a pivotable element configured to be rotatable relative to the fixed element; and a resilient pivot mechanism disposed between the fixed element and the pivotable element and coupled to the fixed element and the pivotable element to form a pivot such that the pivotable element is rotatable about the pivot, and a weight having a predetermined weight value coupled to the pivotable element such that when a shear testing tool exerts a force on the pivotable element, the pivotable element rotates to lift the weight to thereby calibrate the shear testing tool based on the force exerted by the shear testing tool and the predetermined weight value of the weight.

2. The apparatus of claim 1, wherein: the pivotable element defines a first length in a horizontal direction and a second length in a vertical direction relative to the pivot; the weight is coupled to an end of the first length distal from the pivot; and the shear testing tool is operable to exert a substantially horizontal force on an end of the second length distal from the pivot to rotate the pivotable element and lift the weight.

3. The apparatus of claim 1, wherein the resilient pivot mechanism comprises a cross-spring pivot mechanism.

4. The apparatus of claim 3, wherein the cross-spring pivot mechanism is formed by a first spring leaf having an opening and a second spring leaf sized to pass through the opening of the first spring leaf, the first and second spring leaves being angularly disposed relative to one another.

5. The apparatus of claim 4, wherein each of the first and second spring leaves has a first edge fixed to the fixed element and a second edge fixed to the pivotable element such that each of the first and second spring leaves is deflectably in contact with the fixed element and the pivotable element.

6. The apparatus of claim 4, wherein the first and second spring leaves are mounted perpendicular to one another.

7. The apparatus of claim 1, wherein the fixed element has opposing first and second sides positioned along an interface between the fixed element and the pivotable element, and the resilient pivot mechanism comprises a first pair of spring leaves mounted on the first side of the fixed element and a second pair of spring leaves mounted on the second side of the fixed element, each spring leaf being deflectably in contact with the fixed element and the pivotable element.

8. The apparatus of claim 7, wherein the spring leaves of the first pair are mounted perpendicular to one another and the spring leaves of the second pair are also mounted perpendicular to one another.

9. The apparatus of claim 1, further comprising a coupling device configured to detachably couple the weight to the pivotable element.

10. The apparatus of claim 9, wherein, the coupling device comprises a hook, the weight being configured to be hung on the hook.

11. The apparatus of claim 1, wherein the shear test tool comprises a shear test rod and a force sensor coupled to the shear test rod, the force sensor operable to measure a force exerted by the shear test rod onto the pivotable element in order to rotate the pivotable element and lift the weight.

12. The apparatus of claim 11, further comprising a processor operably connected to the force sensor, the processor configured to determine a relatively constant force measured by the force sensor after the weight has been lifted from a rest position by the force exerted by the shear test rod.

13. The apparatus of claim 11, wherein the shear test rod has a tapered tip.

14. A method for calibrating a shear test tool, the method comprising: providing a calibration apparatus comprising a fixed element, a pivotable element configured to be rotatable relative to the fixed element, and a resilient pivot mechanism disposed between and coupled to the fixed element and the pivotable element to form a pivot axis such that the pivotable element is rotatable about the pivot axis; and a weight having a predetermined weight value coupled to the pivotable element; and applying a force on the pivotable element using the shear test tool such that the pivotable element rotates about the pivot axis to lift the weight coupled to the pivotable element, thereby calibrating the shear test tool based on the force applied by the shear test tool and the predetermined weight value of the weight.

15. The method of claim 14, wherein the pivotable element defines a first length in a horizontal direction and a second length in a vertical direction relative to the pivot axis, wherein the method further comprises: coupling the weight to an end of the first length distal from the pivot axis; and wherein the step of applying the force on the pivotable element comprises applying a substantially horizontal force on an end of the second length distal from the pivot axis with the shear test tool to rotate the pivotable element and lift the weight.

16. The method of claim 14, wherein the resilient pivot mechanism comprises a cross-spring pivot mechanism.

17. The method of claim 16, wherein the cross-spring pivot mechanism is formed by a first spring leaf having an opening and a second spring leaf sized to pass through the opening of the first spring leaf, the first and second spring leaves being angularly arranged relative to one another.

18. The method of claim 14, wherein the fixed element has opposing first and second sides positioned along an interface between the fixed element and the pivotable element, and the resilient pivot mechanism comprises a first pair of spring leaves mounted on the first side of the fixed element and a second pair of spring leaves mounted on the second side of the fixed element, each spring leaf being deflectably in contact with the fixed element and the pivotable element. moving the shear test rod to apply the force on the pivotable element; ​ 19. The method of claim 14, wherein the shear testing tool comprises a shear testing bar and a force sensor coupled to the shear testing bar, and the method further comprises: ​ and measuring, with the force sensor, the force exerted by the shear test rod onto the pivotable element in order to rotate the pivotable element and lift the weight.

20. The method of claim 19, further comprising: after the weight has been lifted from a rest position by the force exerted by the shear test rod, determining, with a processor or computing system, a relatively constant force measured by the force sensor.

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