Compliant mechanism for improving reaction torque sensing in robotic actuators
A robotic system has a bracket that helps integrate a load sensor into a robotic actuator such that the sensor is not overly affected by loads not aligned with its load sensing axis (which can lead to inaccurate measurements of the desired load). The bracket includes: (a) a tube having an exterior wall and a hollow interior, (b) a first beam between first and second voids, a second beam between a third void and the second void, a third beam between the first void and a fourth void, a fourth beam between the third and fourth voids. The bracket further includes: (a) additional first, second, third, and fourth voids; (c) an additional first beam between the additional first and second voids, an additional second beam between the additional third and second voids, an additional third beam between the additional first and fourth voids, and an additional fourth beam between the additional third and fourth voids.
1 . An exoskeleton robotic system comprising:
a shaft coupled to a linkage;
a bearing that couples the shaft to a housing;
an actuator that includes a motor;
an exoskeleton robotic joint configured to rotate the shaft and linkage about the bearing;
a reaction torque sensor configured to sense torque transmitted to the reaction torque sensor via the joint in response to the motor rotating the shaft and the linkage; and
a bracket including: (a) a tube having an exterior wall and a hollow interior, (b) first, second, third, and fourth voids that each extend from the exterior wall to the hollow interior; (c) a first beam between the first and second voids, a second beam between the third and second voids, a third beam between the first and fourth voids, and a fourth beam between the third and fourth voids;
wherein the bracket includes: (a) an additional first void, an additional second void, an additional third void, and an additional fourth void, the additional first, second, third, and fourth voids each extending from the exterior wall to the hollow interior; (c) an additional first beam between the additional first and second voids, an additional second beam between the additional third and second voids, an additional third beam between the additional first and fourth voids, and an additional fourth beam between the additional third and fourth voids;
wherein the bracket couples the actuator to the housing.
2 . The system of claim 1 , wherein:
the tube has a long axis extending through the hollow interior and from a first end of the bracket to a second end of the bracket;
a first axis intersects the first beam and the first and second voids, a second axis intersects the second beam and the third and second voids, a third axis intersects the third beam and the first and fourth voids, and a fourth axis intersects the fourth beam and the third and fourth voids;
the first, second, third, and fourth axes are all parallel to the long axis.
3 . The system of claim 1 , wherein:
the tube has a proximal third, a distal third, and a middle third between the proximal and distal thirds;
a minimum outer diameter of the proximal third of the tube is greater than a maximum outer diameter of the middle third of the tube;
a minimum outer diameter of the distal third of the tube is greater than the maximum outer diameter of the middle third of the tube;
at least a portion of the reaction torque sensor is located on the middle third of the tube.
4 . The system of claim 3 , wherein:
the reaction torque sensor includes a strain gauge located on the exterior wall of the middle third of the tube;
the shaft and the bearing are both included in the hollow interior of the bracket.
5 . The system of claim 2 , wherein:
the bracket includes a first flange at the first end of the bracket and a second flange at the second end of the bracket;
each of the first, second, third, and fourth axes intersect both the first and second flanges;
the first flange is between the actuator and the second flange.
6 . The system of claim 2 , wherein a fifth axis is parallel to the long axis and intersects the second void but does not intersect the first void and does not intersect the third void.
7 . The system of claim 2 , wherein the first axis intersects the additional first beam and the additional first and second voids, the second axis intersects the additional second beam and the additional third and second voids, the third axis intersects the additional third beam and the additional first and fourth voids, and the fourth axis intersects the additional fourth beam and the additional third and fourth voids.
8 . The system of claim 5 , wherein:
the bracket couples the actuator to the housing;
the housing couples the bracket to the bearing;
the bracket couples to the actuator via the first flange; and
the bracket couples to the housing via the second flange.
9 . The system of claim 8 , wherein the bracket is a compliant element.
10 . The system of claim 8 , wherein:
the bracket has first, second, and third translational degrees of freedom;
the bracket has first and second rotational degrees of freedom but not a third rotational degree of freedom.
11 . The system of claim 8 , wherein the bracket is statically coupled to the reaction torque sensor and is statically coupled to the housing.
12 . The robotic system according to any of claim 11 , wherein the bracket is not slidingly coupled to the housing.
13 . The system of claim 1 , wherein the bracket is a compliant mechanism having compliance: (a) translationally along each of X, Y, Z axes, and (b) rotationally about two of the X, Y, Z axes but not a third of the X, Y, Z axes.
14 . The system of claim 13 , wherein:
the motor is configured to rotate the shaft about the third of the X, Y, Z axes; and
the reaction torque sensor is configured to sense torque transmitted about a sensing axis;
the sensing axis is parallel to the third of the X, Y, Z axes.
15 . The system of claim 14 , wherein the sensing axis is colinear with the third of the X, Y, Z axes.
16 . The system of claim 14 , wherein:
the first beam is configured to be in tension when the second beam is in compression in response to a first force on the first beam; and
the first beam is configured to be in compression when the second beam is in tension in response to a second force on the first beam;
the first and second forces are directed along one of the X, Y, Z axes;
the first and second forces are opposite in direction to one another.
17 . The system of claim 14 , wherein the reaction torque sensor includes a Wheatstone bridge.
18 . The system of claim 1 , wherein the bracket has a dumbbell shape.
19 . The system of claim 18 , wherein:
the tube has a long axis extending through the hollow interior and from a first end of the bracket to a second end of the bracket;
the first, second, third, and fourth beams are coplanar with each other in a plane that is orthogonal to the long axis.
20 . The system of claim 1 , wherein:
the tube has a long axis extending through the hollow interior and from a first end of the bracket to a second end of the bracket;
a plane, which is orthogonal to the long axis, intersects the shaft, the bearing, and the bracket.
21 . A robotic system comprising:
a shaft coupled to a robotic appendage;
a bearing that couples the shaft to a housing;
an actuator that includes a motor;
a robotic joint to rotate the shaft and a linkage via the bearing;
a torque sensor to sense torque created when the motor rotates the appendage; and
a bracket including: (a) a rod having an exterior wall, (b) first and second voids in the exterior wall; (c) a beam between the first and second voids, and (d) first and second ends;
wherein the bracket is a compliant element and couples: (a) to the actuator via the first end, (b) to the housing via the second end, (c) the actuator to the housing;
wherein: (a) the bracket has a proximal third, a distal third, and a middle third between the proximal and distal thirds; (b) a maximum outer diameter of the proximal third of the bracket is greater than a minimum outer diameter of the middle third of the bracket; (c) a maximum outer diameter of the distal third of the bracket is greater than the minimum outer diameter of the middle third of the bracket;
wherein at least a portion of the torque sensor is located on the middle third of the bracket.
22 . The system of claim 21 , wherein the torque sensor includes a strain gauge on the bracket between the first and second ends.
23 . The system of claim 22 , wherein the bracket has compliance: (a) translationally along each of X, Y, Z axes, and (b) rotationally about two of the X, Y, Z axes but not a third of the X, Y, Z axes.
24 . The system of claim 23 , wherein:
the motor is configured to rotate the shaft about the third of the X, Y, Z axes;
the torque sensor is to sense torque transmitted about a sensing axis; and
the sensing axis is colinear with the third of the X, Y, Z axes.
25 . The system of claim 24 , wherein the rod is hollow and the shaft and the bearing are both included in a hollow interior of the bracket.