Force and torque sensing method and means for manipulators and the like

• US 3,921,445 A
• Filed: 10/15/1973
• Issued: 11/25/1975
• Est. Priority Date: 10/15/1973
• Status: Expired due to Term

• Current Assignee: Antony J. Sword, John W. Hill
• Original Assignee: Antony J. Sword, John W. Hill
• Inventors: Hill, John W., Sword, Antony J.
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US05/406,553
• Time in Patent Office: 771 Days
• Field of Search: 73/133R 250/231R,231P 244/83E 214/1CM
• US Class Current: 73/862.043
• CPC Class Codes: B25J 19/021 Optical sensing devices
• CPC Class Codes: G01L 1/24 by measuring variations of optical properties of material when it is stressed, e.g. by photoelastic stress analysis using infrared, visible light, ultraviolet
• CPC Class Codes: G01L 5/163 of potentiometers
• CPC Class Codes: G01L 5/166 using photoelectric means
• CPC Class Codes: G01L 5/226 to manipulators, e.g. the force due to gripping

Abstract

A manipulator is shown of the type which includes an effector, such as a hand, comprising a pair of jaws relatively pivotally movable between open and closed positions under operation of power means such as an electric motor. Sensing means, for sensing both magnitude and direction of forces along three mutually orthogonal axes intersecting at the wrist and for sensing magnitude and direction of torques about said axes, are provided at the wrist intermediate to the manipulator hand and hand supporting means. The sensing means includes a plurality of sensing units radially spaced from the longitudinal axis of the manipulator at equal distances therefrom. In an exemplary arrangement, four such orthogonally located sensing units are employed, each of which includes a radially extending opaque pin carried by the manipulator arm or hand. Each pin extends into a clearance hole formed in an energy source and detector housing carried by the other of the arm and hand. The housings also are formed with passages which intersect the pin receiving hole and along which passages an associated energy source and energy detector are located, with the energy from the source being directed toward the energy detector. A portion of the energy from each of the sources is blocked by the pin such that only the unobstructed portion of the energy from the source reaches the detector. The amount of shadowing of energy by the pins depends upon forces and torques applied to the hand, and the outputs from the detectors are combined in such a manner as to provide output signals representative of the three components of force at the wrist corresponding to reach, lift and sweep directions of hand motion and the three components of torque corresponding to twist, turn and tilt of the hand. Also, the hand and power means for operation of the hand are located at opposite sides of the wrist, such that the power means functions as a counterweight to balance the weight of the hand. Consequently, the hand weight is not reflected in the outputs of the torque sensors.

Claims

1. Sensing means for use in sensing at least one component of force and torque components along mutually orthogonal X, Y and Z axes transmitted between first and second members having a longitudinal axis extending along the Z axis, said sensing means comprising:

resilient coupling means coupling said first and second members to allow for relative movement therebetween and through which said X, Y and Z axes extend;

a plurality of sensing units radially displaced from said Z axis at the resilient coupling means, each of which sensing units includes first and second cooperating means attached to said coupled first and second members, respectively, so that relative movement between said first and second cooperating means is produced upon transmission of forces and torques between said coupled first and second members through said resilient coupling means;

said forces and torques being transmitted through said resilient coupling means substantially independently of said sensing units, and means for obtaining at least first and second electrical outputs from each of said sensing units, the outputs from each sensing unit being respectively responsive only to relative movement of said cooperating means along a first direction perpendicular to the radius extending from the Z axis through the associated sensing unit and responsive only to relative movement of said cooperating means along a direction mutually orthogonal to said associated first direction and radius.

2. The sensing means as defined in claim 1 wherein said sensing units are of the non-piezoelectric type.

3. The sensing means as defined in claim 1 wherein:

said plurality of said sensing units are circumferentially spaced about said longitudinal axis at the resilient coupling means; and

including means for connecting electrical outputs from different sensing units together in circuit arrangements having outputs algebraically related to said electrical outputs from said sensing units.

4. The sensing means as defined in claim 1 wherein said first and second cooperating means of each said sensing unit include an opaque member and spaced apart light source and photocell, respectively, arranged so that light from the source is directed toward said photocell past an edge of said opaque member, which opaque member blocks a variable portion of the light preventing the same from reaching the photocell.

5. The sensing means as defined in claim 1 wherein Said first and second cooperating means of each of said sensing units include a potentiometer comprising a resistive element with parallel extending terminals along opposite edges thereof and a contact in movable engagement with the resistive element, respectively.

6. The sensing means as defined in claim 1 wherein said first and second cooperating means of each said sensing unit include a pair of adjacent photocell elements and a light source, respectively, arranged so that light from the source is directed radially onto both of said photocell elements.

7. The sensing means as defined in claim 1 which includes:

first and second of said sensing units diametrically oppositely located along said Y axis;

said first and second electrical outputs from each of said sensing units being responsive only to relative movement of said cooperating means along directions parallel to said X and Z axes, respectively.

8. The sensing means as defined in claim 7 including:

means for connecting electrical outputs from said first and second sensing units together in circuit arrangements having outputs algebraically related thereto, one of said circuit arrangements having an output indicative of force transmitted along said X axis, and another of said circuit arrangements having an output indicative of torque about the X axis.

9. The sensing means as defined in claim 8 wherein another of said circuit arrangements has an output indicative of torque about the Z axis.

10. The sensing means as defined in claim 8 wherein another of said circuit arrangements has an output indicative of force transmitted along said Z axis.

11. The sensing means as defined in claim 8 including:

a second pair of said sensing units diametrically oppositely located along said X axis, said first and second electrical outputs from each sensing unit of said second pair thereof being responsive only to relative movement of said cooperating means along directions parallel to said Y and Z axes, respectively;

means for connecting the electrical outputs from said second pair of sensing units together in circuit arrangements having outputs indicative of force transmitted along and transmitted torque about said Y axis.

12. Sensing means for use in sensing at least one component of force and torque components along mutually orthogonal X, Y and Z axes transmitted between first and second members having a longitudinal axis extending along the Z axis, said sensing means comprising:

resilient coupling means coupling said first and second members to allow for relative movement therebetween and through which said X, Y and Z axes extend;

at least one sensing unit radially displaced along the Y axis from said Z axis at the resilient coupling means, which sensing unit includes first and second cooperating means attached to said coupled first and second members, respectively, so that relative movement between said first and second cooperating means is produced upon transmission of forces and torques between said coupled first and second members through said resilient coupling means; and

means for obtaining a first electrical output from said sensing unit responsive only to relative movement of said cooperating means along a first direction parallel to said longitudinal axis;

said first and second members comprising a manipulator and effector and end effector supporting means, respectively, interconnected by said resilient coupling means.

13. The sensing means as defined in claim 12 wherein said end effector comprises:

a pair of relatively movable members;

a motor for operating said movable members; and

means for mounting said motor along said Z axis at the side opposite sais sensing unit from the manipulator end effector to counterbalance said end effector.

14. Sensing means for use in sensing components of force and torque along mutually orthogonal X, Y and Z axes extending through resilient coupling means coupliNg first and second members together, said Z axis extending longitudinally therethrough;

at least three sensing units circumferentially spaced about said Z axis about said resilient coupling means;

each of said sensing units including first and second cooperating means attached to said coupled first and second members, respectively, so that relative movement between said first and second cooperating means is produced upon transmission of forces and torques through said resilient coupling means;

means for obtaining first electrical outputs from each of said sensing units responsive only to relative movement of said cooperating means along a direction parallel to said Z axis;

first circuit means;

means for combining said first electrical outputs in said first circuit means for obtaining outputs indicative of torque components about said X and Y axes and the force component along said Z axis;

means for obtaining second electrical output from each of said sensing units responsive only to relative movement of said cooperating means along a direction mutually orthogonal to the radius through said sensing unit and the direction parallel to said Z axis;

second circuit means; and

means for combining said second electrical outputs in said second circuit means for obtaining outputs indicative of the force components along said X and Y axes and the torque component about said Z axis.

15. The sensing means as defined in claim 14 wherein there are four of said sensing units circumferentially spaced about the Z axis along said X and Y axes.

16. The sensing means as defined in claim 14 wherein said first and second cooperating means include an opaque member and spaced apart light source and photocell, respectively, arranged so that light from the source is directed toward said photocell past an edge of said opaque member, which opaque member blocks a variable portion of the light preventing the same from reaching the photocell.

17. The sensing means as defined in claim 14 wherein said first and second cooperating means of each sensing unit include a potentiometer comprising a resistive element with parallel extending terminals along opposite edges thereof and a contact in movable engagement with the resistive element, respectively.

18. The sensing means as defined in claim 14 wherein said first and second cooperating means include a pair of adjacent photocell elements and a light source, respectively, arranged so that light from the source is directed radially onto both of said photocell elements.

19. The sensing means as defined in claim 14 wherein said first and second members comprise a manipulator end effector and end effector supporting means, respectively, interconnected by said resilient coupling means.

20. The sensing means as defined in claim 19 wherein said end effector comprises:

a pair of relatively movable members;

a motor for operating said movable members; and

means for mounting said motor along said Z axis at the side opposite said sensing unit from the manipulator end effector to counterbalance said end effector.

21. A method of sensing components of torque and force transmitted between first and second members along mutually orthogonal X, Y and Z axes comprising:

attaching said first and second members together by resilient coupling means through which substantially the entire force and torque components are transmitted between said first and second members;

attaching a plurality of two-part sensing units, at circumferentially spaced locations about the Z axis in the plane of the X and Y axes, to said first and second members such that relative movement between the two parts of the sensing units is produced upon transmission of forces and torques through said resilient coupling means;

obtaining first electrical outputs from the sensing units in response to relative movement of the two parts along a direction parallel to the Z axis;

combining the first electrical outputs in different combination to obtain outputs related to torque components about said X and Y axes and the force component transmitted along said Z axis;

obtaining second electrical outputs from the sensing units in response to relative movement of the two parts of each sensing unit along a direction mutually orthogonal to the associated radius through said sensing unit and the direction parallel to the Z axis; and

combining the second electrical outputs from the sensing units in different combinations to obtain outputs related to force components transmitted along said X and Y axes and the torque component about said Z axis.

22. Sensing means for use in sensing at least one component of force and torque components transmitted between first and second members having a longitudinal axis extending therebetween comprising:

resilient coupling means coupling said first and second members to allow for relative movement therebetween;

an opaque member located along a radius extending from said longitudinal axis;

housing means having a clearance hole into which said opaque member extends;

means for attaching said opaque member and housing means to said first and second members so that relative movement is produced therebetween upon transmission of force and force moments through said resilient coupling means;

means forming at least one light passage in said housing means which intersects with said clearance hole formed therein; and

light source and light sensing means at said light passage with said light sensing means arranged to receive light emitted by said light source after passing an edge of said opaque member which blocks a variable portion of the light depending upon force and force moments transmitted by said resilient coupling means.

23. The sensing means as defined in claim 22 including;

a plurality of said light passages formed in said housing means which intersect with said clearance hole and extending along generally perpendicular axes, and light source and light sensing means at opposite ends of each of said light passages.