Patent Description:
Single-axis load cells are widely used in automation industries as well as research laboratories. Existing single-axis load cells commonly measure deflections using strain gauges, which require a sophisticated sensing structure. The sensors used can be sensitive to manufacturing tolerances, temperature changes, and impact loads, and require recalibration frequently. Multiple strain gauges are typically installed exactly opposite one another in the sensing structure to compensate for off-axis loads. The multiple strain gauges can be susceptible to assembling errors.

<CIT> discloses a displacement measurement device including a first structure, a second structure, and a coupling portion configured to couple the first structure with the second structure. The first structure includes a first sensor configured to generate an electrical signal corresponding to displacement between a first attachment portion of the first structure and a second attachment portion of the second structure in the at least one first direction. The second structure includes a second sensor configured to generate an electrical signal corresponding to displacement between the first attachment portion and the second attachment portion in the at least one second direction. <CIT> discloses an optoelectronic array for detecting relative movements or relative positions of two objects. <CIT> relates to a displacement sensor module, especially for a force sensor or a load cell. <CIT> discloses a magnetic torque sensor for a transmission converter driving plate for measuring torque radially transmitted between a shaft and the radially separated part of a disc type member. <CIT> relates to a load sensor unit which is less likely to suffer from hysteresis errors. <CIT> discloses a force sensor with the Z-axis given as a central axis, on an XY-plane, arranged are a rigid force receiving ring, a flexible detection ring inside thereof, and a cylindrical fixed assistant body further inside thereof. Documents <CIT> and <CIT> anticipate sensing devices with Hall sensors and magnets or magnetization zones with different polarities.

Accordingly, the present disclosure aims to provide an axial force sensor, a robot gripper, and a robot having the axial force sensor.

To solve the above-mentioned problem, the subject matter of the independent claims is provided. The dependent claims describe optional embodiments of the invention.

A technical scheme adopted by the present disclosure is to provide an axial force sensor. The axial force sensor may include a sensing diaphragm and at least two signal pairs. The sensing diaphragm includes an inner ring, an outer ring, and a connecting element connected between the inner ring and the outer ring. The connecting element is more compliant in a direction of the axial force to be detected than in other loading directions. Each signal pair includes a signal emitter and a signal receiver. The signal emitter is coupled to one of the inner ring and the outer ring. The signal receiver is coupled to the other of the inner ring and the outer ring.

To solve the above-mentioned problem, another technical scheme adopted by the present disclosure is to provide a robot gripper. The robot gripper includes a catching mechanism and an axial force sensor. The axial force sensor may be utilized to measure a force acting on the catching mechanism. The axial force sensor may include a sensing diaphragm and at least two signal pairs. The sensing diaphragm includes an inner ring, an outer ring, and a connecting element connected between the inner ring and the outer ring. The connecting element is more compliant in a direction of the axial force to be detected than in other loading directions. Each signal pair includes a signal emitter and a signal receiver. The signal emitter is coupled to one of the inner ring and the outer ring. The signal receiver is coupled to the other of the inner ring and the outer ring.

To solve the above-mentioned problem, another technical scheme adopted by the present disclosure is to provide a robot having at least one axial force sensor. The axial force sensor may include a sensing diaphragm and at least two signal pairs. The sensing diaphragm includes an inner ring, an outer ring, and a connecting element connected between the inner ring and the outer ring. The connecting element is more compliant in a direction of the axial force to be detected than in other loading directions. Each signal pair includes a signal emitter and a signal receiver. The signal emitter is coupled to one of the inner ring and the outer ring. The signal receiver is coupled to the other of the inner ring and the outer ring.

According to the present disclosure, the axial force sensor may include multiple pairs of signal emitters and signal receivers. These signal emitters and signal receivers may be used for off-axis load cancellation and temperature compensation. Thus, the axial force sensor may measure the axial force acting thereon more precisely.

In order to clearly explain the technical solutions in the embodiments of the present disclosure, the drawings used in the description of the embodiments will be briefly described below. The drawings in the following description are merely exemplary embodiments of the present disclosure. For those of ordinary skill in the art, other embodiments may also be derived based on these drawings without any creative work.

The disclosure will now be described in detail with reference to the accompanying drawings and examples.

Referring to <FIG>, an axial force sensor <NUM> is illustrated according to certain embodiments of the present disclosure. The axial force sensor <NUM> may include a sensing diaphragm <NUM>, a holding structure <NUM>, a shielding structure <NUM>, and a hard stop <NUM>. As shown in <FIG>, the sensing diaphragm <NUM> may include an inner ring <NUM>, an outer ring <NUM>, a connecting element <NUM>, and a center hole <NUM>. The connecting element <NUM> may be connected between the inner ring <NUM> and the outer ring <NUM>. In certain embodiments, the sensing diaphragm <NUM> may be made of one or more highly robust materials, such as aluminum alloy, titanium alloy, and stainless-steel alloy. The connecting element <NUM> is more compliant in a direction of the axial force to be detected than in other loading directions. For example, the connecting element <NUM> may be moderately compliant in the axial direction of the sensing diaphragm <NUM> but considerably stiff in other loading directions (e.g., stiff against both forces and moments in other loading directions). Therefore, forces and moments in directions other than the force in the axial direction cannot significantly deflect the structure to change the sensor output.

<FIG> illustrates an example cross-sectional view of an axial force sensor <NUM> showing a signal pair <NUM>. Each signal pair <NUM> may include a signal emitter <NUM> and a signal receiver <NUM>. The signal emitter <NUM> and the signal receiver <NUM> may be connected to different parts of the sensing diaphragm <NUM>. That is, in some examples, if the signal emitter <NUM> is coupled to the inner ring <NUM> of the sensing diaphragm <NUM>, the signal receiver <NUM> may be coupled to the outer ring <NUM> of the sensing diaphragm <NUM>. In other examples, if the signal emitter <NUM> is coupled to the outer ring <NUM> of the sensing diaphragm <NUM>, the signal receiver <NUM> may be coupled to the inner ring <NUM> of the sensing diaphragm <NUM>. When an axial load is applied to the outer ring <NUM> (or the inner ring <NUM>) of the sensing diaphragm <NUM>, the outer ring <NUM> deflects from the inner ring <NUM>, which changes the readings of the signal receiver <NUM>.

In some embodiments, the axial force sensor <NUM> may include only two signal pairs <NUM>. The two signal pairs <NUM> may be oppositely arranged along a circumferential direction of the sensing diaphragm <NUM>. When an axial load is applied to the sensing diaphragm <NUM>, the two signal pairs <NUM> may have opposite trends of signal changes, and thus the total force can be derived by subtracting one from the other and then being divided by two (e.g., calculating a differential output). When an off-axis load, for example, a bending moment, is applied to the sensing diaphragm <NUM>, the two signal pairs <NUM> may share the same trend of signal changes, and thus by subtracting one from the other, the deflection caused by this load may be canceled. In another example, signal changes caused by temperature shifts make the two signal pairs change in the same trend, and thus by subtracting one from the other, the temperature shifts can also be suppressed. Most non-resistive sensing methods are not sensitive to temperature changes, and thus even without perfect cancellation, temperature changes have little effect on the sensor.

In various examples of the present disclosure, more pairs (e.g., <NUM>, <NUM>, or more) of signal emitters <NUM> and receivers <NUM> can also be utilized. In such examples, the use of multiple pairs of signal emitters <NUM> and signal receivers <NUM> may enable the axial force sensor <NUM> to measure the axial force acting thereon more precisely by enabling more precise off-axis load cancellation and temperature compensation. In one embodiment, the signal emitter <NUM> may be a magnet and the signal receiver <NUM> may correspondingly be a hall effect sensor.

A hall effect sensor may work as follows. When a hall effect sensor detects the magnetic field strength perpendicular to the magnetization axis (i.e. the Y axis in <FIG>) and is capable of moving along the magnetization axis of a magnet (i.e. the Z axis out of and into the page in <FIG>), the relationship between the displacement of the sensor and the magnetic field strength detected by the sensor is substantially linear. When a hall effect sensor detects the magnetic field strength perpendicular to the magnetization axis (i.e. the Y axis in <FIG>) and is capable of moving perpendicular to the magnetization axis of a magnet (i.e. the Y axis in <FIG>), the relationship between the detected magnetic field strength and the displacement of the sensor is less linear and can be modeled with non-linear functions, e.g., polynomial functions.

Further, when a hall effect sensor detects the magnetic field strength perpendicular to the magnetization axis (i.e. the Y axis in <FIG>) and is capable of moving in a secondary perpendicular direction to the magnetization axis of a magnet (i.e. the X axis in <FIG>), the detected magnetic field strength does not change. Thus, in aspects of the present disclosure in which the signal emitter <NUM> is a magnet and the signal receiver <NUM> is a hall effect sensor, by properly arranging the signal emitter <NUM> and the signal receiver <NUM> and measuring the magnetic field strength detected by the signal receiver <NUM>, the displacement of the outer ring <NUM> with respect to the inner ring <NUM> in the axial direction of the axial force sensor may be derived. Moreover, the relationship between this displacement and the axial force acting on the axial force sensor <NUM> may be acquired (e.g., by modeling the axial force sensor <NUM> or by testing the prototype of the axial force sensor <NUM>). Therefore, the axial force acting on the axial force sensor <NUM> may be obtained based on the readings of the signal receivers <NUM> of the signal pairs <NUM>.

Referring to <FIG>, in some embodiments, the magnetization direction of the magnet 21a (i.e., signal emitter 21a) may be opposite to the magnetization direction of the magnet 21b (i.e., signal emitter 21b). Moreover, the magnetization directions of the magnets 21a and 21b may both be substantially perpendicular to the extending direction of the sensing diaphragm <NUM>. That is, the magnetization directions of the magnets 21a and 21b may be parallel to the axial direction of the axial force sensor <NUM>.

As shown in <FIG>, the hall effect sensors 22a and 22b (i.e. signal receivers 22a and 22b) may be spaced from the corresponding magnets 21a and 21b in the radial direction of the sensing diaphragm <NUM>. In this way, when axial force is applied on the axial force sensor <NUM>, the hall effect sensors 22a and 22b may move in the axial direction of the axial force sensor <NUM> with respect to the magnets 21a and 21b. Thus, the relationship between the displacement of the hall effect sensors 22a and 22b and the detected magnetic field strength may be substantially linear, which may facilitate the modeling of the structure and the calculation of the axial force. In other embodiments, the two signal pairs <NUM> may be arranged to have the same trend of signal changes when the axial load is applied on the axial force sensor <NUM>. In this situation, the above-described subtraction method may no longer be applicable, and the outputs of the two signal pairs <NUM> may be processed differently, for example, by applying a polynomial fit.

It should be appreciated that the arrangement of the signal pairs <NUM> shown in <FIG> is merely illustrative and the signal pairs <NUM> may be arranged in other configurations. For example, <FIG> show several possible configurations of each of the signal pairs <NUM> of the axial force sensor <NUM>, where the Z direction represents the axial direction of the axial force sensor <NUM> and the Y direction represents the radial direction of the axial force sensor <NUM>. In some of these configurations, the relationship between the axial displacement of the hall effect sensor (i.e., the signal receiver <NUM>) with respect to the corresponding magnet (i.e., the signal emitter <NUM>) and the detected magnetic field strength may not be linear. However, as long as the relative axial displacement of the hall effect sensor may significantly influence the value of the detected magnetic field strength, it can be utilized to calculate the axial force applied on the axial force sensor <NUM>.

Referring to <FIG>, the holding structure <NUM> of the axial force sensor <NUM> may include a center shaft <NUM> and a supporting plate <NUM>. The holding structure <NUM> may be made from rigid material in some aspects. For example, the holding structure <NUM> may be made from the same material as the sensing diaphragm <NUM>. The inner ring <NUM> of the sensing diaphragm <NUM> may define a center hole <NUM>. The center shaft <NUM> may pass through the center hole <NUM> and, in some examples, may be coupled to the inner ring <NUM>. The supporting plate <NUM> may be connected to the center shaft <NUM> and may extend substantially parallel to the sensing diaphragm <NUM>.

In some aspects, the holding structure <NUM> and the sensing diaphragm <NUM> may be separate components. In other aspects, the holding structure <NUM> and the sensing diaphragm may be manufactured as one single component. In some examples, the holding structure <NUM> may provide more space for installing the components of the axial force sensor <NUM>, and may facilitate the connection between the axial force sensor <NUM> and other external components. For example, the axial force sensor <NUM> may be utilized in a robot actuator, and the holding structure <NUM> may be connected to a driven end of a motor assembly or to an output end (e.g., output flange) of the actuator.

In some embodiments, as shown in <FIG>, the signal emitter <NUM> may be installed on the outer ring <NUM> while the signal receiver <NUM> is installed on the supporting plate <NUM> and aligned with the signal emitter <NUM> in either the axial direction or the radial direction of the sensing diaphragm <NUM>. In such embodiments, since the holding structure <NUM> is coupled to the inner ring <NUM> of the sensing diaphragm <NUM>, the signal receiver <NUM> is also coupled to the inner ring <NUM> indirectly. In other embodiments, the signal receiver <NUM> may be installed on the outer ring <NUM> while the signal emitter <NUM> is installed on the supporting plate <NUM> and aligned with the signal receiver <NUM> in either the axial direction or the radial direction of the sensing diaphragm <NUM>. In such other embodiments, the signal receiver <NUM> is coupled to the outer ring <NUM> while the signal emitter <NUM> is coupled to the inner ring <NUM>.

In some embodiments, the axial force sensor <NUM> may further include a shielding structure <NUM>. In some aspects, the shielding structure <NUM> may be installed on the supporting plate <NUM> and located corresponding to the signal pairs <NUM> in the circumferential direction of the sensing diaphragm <NUM>. The shielding structure <NUM> may enclose the signal pairs <NUM> to protect the signal pairs <NUM> from signal disruption and/or interference. In some examples, the structure and material of the shielding structure <NUM> may be based on the type of the signal pairs <NUM>. For example, if magnetic signals are used in the signal pairs <NUM>, the shielding structure <NUM> may be made from high magnetic permeability material such as supermalloy, super mumetal alloys, sanbold, permalloy, carbon steel, martensite steel, etc..

In some embodiments, the axial force sensor <NUM> may further include a hard stop <NUM>. The hard stop <NUM> may be installed on the supporting plate <NUM> and may enclose the outer ring <NUM> of the sensing diaphragm <NUM>. The hard stop <NUM> may have, for example, a C-shaped configuration. In other examples, the hard stop <NUM> may take any number of different suitable configurations. In some aspects, there may exist clearances (not shown) between the hard stop <NUM> and the outer ring <NUM> on both the upper and lowers sides, and the hard stop <NUM> may be utilized to prevent over deflection of the outer ring <NUM>. When excessive deflection occurs with overload, the rigid hard stop <NUM> may prevent further deflection of the outer ring <NUM>, thus protecting the sensing diaphragm <NUM> from yielding and fatigue. In some examples, the axial force sensor <NUM> may have only one hard stop <NUM> as illustrated figures. In other examples, the axial force sensor <NUM> may have more than one hard stop <NUM>.

The present disclosure also provides for a robot gripper. As shown in <FIG>, the robot gripper <NUM> may include a catching mechanism <NUM> and an axial force sensor <NUM>. The axial force sensor <NUM> may be utilized to measure the force acting on the catching mechanism <NUM>. The structure and function of the axial force sensor <NUM> may be similar to any axial force sensor of the embodiments described above (e.g., the example axial force sensor <NUM>). The robot gripper <NUM> may further include a driving assembly <NUM> and a shell <NUM>. The driving assembly <NUM> may be coupled to the axial force sensor <NUM> and configured to drive the catching mechanism <NUM>. The catching mechanism <NUM> and the driving assembly <NUM> may be installed on the shell <NUM> in any suitable way.

Claim 1:
An axial force sensor (<NUM>), comprising
a sensing diaphragm (<NUM>) comprising:
an inner ring (<NUM>);
an outer ring (<NUM>); and
a connecting element (<NUM>) connected between the inner ring (<NUM>) and the outer ring (<NUM>), wherein the connecting element (<NUM>) is more compliant in a direction of the axial force to be detected than in other loading directions; and
at least two signal pairs (<NUM>) comprising a first signal pair and a second signal pair oppositely arranged along a circumferential direction of the sensing diaphragm, each of the at least two signal pairs (<NUM>) comprising:
a signal emitter (<NUM>) coupled to one of the inner ring (<NUM>) and the outer ring (<NUM>), wherein the signal emitter (<NUM>) is a magnet; and
a signal receiver (<NUM>) coupled to the other of the inner ring (<NUM>) and the outer ring (<NUM>), wherein the signal receiver (<NUM>) is a hall effect sensor, wherein:
a magnetization direction of the magnet of the first signal pair is opposite to a magnetization direction of the magnet of the second signal pair;
both the magnetization direction of the magnet of the first signal pair and the magnetization direction of the magnet of the second signal pair are perpendicular to an extending direction of the sensing diaphragm (<NUM>); and
the hall effect sensor of each of the first signal pair and the second signal pair is spaced from the corresponding magnet in a radial direction of the sensing diaphragm (<NUM>).