Force and torque sensor with overload structure and method for manufacturing
A force/torque sensor includes an outer body structure, an inner body structure, and three sensor structures extending between the outer body structure and the inner body structure. Overload structures are positioned between the sensor structures. An overload structure includes an outer portion that has a plurality of outer facets, and an inner portion that has a plurality of corresponding opposing inner facets. The outer facets and the inner facets are configured to permit a limited predetermined amount of relative motion between the inner body structure and the outer body structure in at least six degrees of freedom from a neutral position, and to inhibit relative motion between the inner body structure and the outer body structure beyond the predetermined amount. An overload structure may be formed by separating a bridge using wire-cut electrical discharge machining, optionally performed in a single pass.
1 . A force/torque sensor comprising:
an outer body structure;
an inner body structure;
three sensor structures, each sensor structure extending between the outer body structure and the inner body structure; and
three overload structures, each overload structure being positioned between two of the three sensor structures;
wherein each of the three overload structures includes an outer portion extending inwardly from the outer body structure, and an inner portion extending outwardly from the inner body structure, and
wherein the outer portion of each overload structure has a plurality of outer facets including a first outer facet and a second outer facet, the inner portion has a plurality of corresponding opposing inner facets including a first inner facet and a second inner facet, the first inner facet corresponding to and opposing the first outer facet and the second inner facet corresponding to and opposite the second outer facet, and the plurality of outer facets and the plurality of inner facets are configured to permit a limited predetermined amount of relative motion between the inner body structure and the outer body structure in at least six degrees of freedom from a neutral position, and to inhibit relative motion between the inner body structure and the outer body structure beyond the predetermined amount, the first inner facet and the first outer facet limiting displacement of the inner body structure and the outer body structure in response to an external force in a positive direction along a Z axis of the force/torque sensor, the second inner facet and the second outer facet limiting displacement of the inner body structure and the outer body structure in response to an external force in a negative direction along the Z axis.
2 . The force/torque sensor claim 1 , wherein the three sensor structures and the three overload structures are spaced generally equidistantly from each other.
3 . The force/torque sensor of claim 1 , wherein, when the outer body structure and the inner body structure are in the neutral position, a gap between each of the plurality of outer facets and the corresponding one of the plurality of inner facets has a distance of between about 25 microns to 0.5 mm.
4 . The force/torque sensor of claim 1 , wherein each of the three sensor structures has a width of between about 1 to 25 mm.
5 . The force/torque sensor of claim 4 , wherein each of the three sensor structures has a width of between about 2 to 12 mm.
6 . The force/torque sensor of claim 1 , further comprising a strain sensor secured to each of the three sensor structures.
7 . The force/torque sensor of claim 6 , wherein the strain sensor comprises a metal-foil strain gauge.
8 . The force/torque sensor of claim 1 , wherein each of the sensor structures extends between the inner body structure and the outer body structure along a plane defined by an X axis of the force/torque sensor perpendicular to the Z axis and a Y axis of the force/torque sensor perpendicular to the X axis and the Z axis.
9 . The force/torque sensor of claim 1 , wherein the first inner facet, the second inner facet, the first outer facet and the second outer facet each includes a face angled relative to the Z axis.
10 . The force/torque sensor of claim 9 , wherein the face of each of the first inner facet and the second outer facet is directed in the negative direction along the Z axis, and the face of each of the first outer facet and the second inner facet is directed in the positive direction along the Z axis.
11 . The force/torque sensor of claim 1 , wherein the outer body structure and the inner body structure are formed from a single blank of metal.
12 . A method of manufacturing a force/torque sensor frame comprising an outer body structure, an inner body structure, at least one sensor structure extending between the outer body structure and the inner body structure, and at least one overload structure, the method comprising:
providing a body structure comprising the outer body structure, the inner body structure, the at least one sensor structure extending between the outer body structure and the inner body structure, and at least one overload bridge extending between the outer body structure and the inner body structure; and
separating, via wire-cut electrical discharge machining, each of the at least one overload bridge into an outer portion extending from the outer body structure and an inner portion extending from the inner body structure, the outer portion having a plurality of outer facets including a first outer facet and a second outer facet, and the inner portion having a plurality of corresponding opposing inner facets including a first inner facet and a second inner facet, the first inner facet corresponding to and opposing the first outer facet and the second inner facet corresponding to and opposite the second outer facet, and
wherein the first inner facet and the first outer facet limit displacement of the inner body structure and the outer body structure in response to an external force in a positive direction along a Z axis of the force/torque sensor, the second inner facet and the second outer facet limit displacement of the inner body structure and the outer body structure in response to an external force in a negative direction along the Z axis.
13 . The method of claim 12 , wherein the wire-cut electrical discharge machining is performed in a single pass.
14 . The method of claim 12 , wherein the plurality of outer facets are formed during a first pass of the wire-cut electrical discharge machining, and the plurality of inner facets are formed during a second pass of the wire-cut electrical discharge machining.
15 . The method of claim 12 , wherein when the outer body structure and the inner body structure are in a neutral position, a gap between each of the plurality of outer facets and the corresponding one of the plurality of inner facets has a distance of between about 25 microns to 0.5 mm.
16 . The method of claim 12 , wherein the three sensor structures and the three overload structures are spaced generally equidistantly from each other.
17 . The method of claim 12 , wherein each of the sensor structures extends between the inner body structure and the outer body structure along a plane defined by an X axis of the force/torque sensor perpendicular to the Z axis and a Y axis of the force/torque sensor perpendicular to the X axis and the Z axis.
18 . The method of claim 12 , wherein the first inner facet, the second inner facet, the first outer facet and the second outer facet each includes a face angled relative to the Z axis.
19 . The method of claim 18 , wherein the face of each of the first inner facet and the second outer facet is directed in the negative direction along the Z axis, and the face of each of the first outer facet and the second inner facet is directed in the positive direction along the Z axis.
20 . The method of claim 12 , wherein the outer body structure and the inner body structure are formed from a single blank of metal.