Transducer with six degrees of freedom

• US 4,369,663 A
• Filed: 02/03/1981
• Issued: 01/25/1983
• Est. Priority Date: 03/07/1980
• Status: Expired due to Fees

• Current Assignee: Centro Ricerche FIAT SPA
• Original Assignee: Centro Ricerche FIAT SPA
• Inventors: Salvatore, Osvaldo, Venturello, Giorgio
• Primary Examiner(s): Ruehl, Charles A.
• Application Number:
  US06/231,065
• Time in Patent Office: 721 Days
• Field of Search: 73/862.04, 73/862.05, 73/862.06, 361/280, 361/283, 361/290, 361/292
• US Class Current: 73/862.043
• CPC Class Codes: B25J 13/02 Hand grip control means handles or pedals for crane control B66C13/56; for measuring the force applied to control members G01L5/22; hand-held casings for switching devices, e.g. joy-sticks H01H9/0214
• CPC Class Codes: B25J 13/085 Force or torque sensors B25J13/082, B25J13/084 take precedence
• CPC Class Codes: G01L 1/144 with associated circuitry G01L1/146 and G01L1/148 take precedence
• CPC Class Codes: G01L 5/165 using variations in capacitance
• CPC Class Codes: G05G 9/04737 with six degrees of freedom

Abstract

A transducer having six degrees of freedom is provided for converting forces and moments applied to a movable member, particularly to the movable arm of a robot, into electrical signals. The transducer includes a cylindrical body which is intended to be connected to the movable member and whose lateral surface has two axially spaced portions each provided with four equiangularly spaced metal plates. A cylindrical casing is resiliently supported about the body and provided on its inner surface with two substantially semi-cylindrical metal plates arranged facing the plates carried by the body in such a way as to define therewith a narrow interspace and to constitute eight capacitors. The capacitances of these capacitors depend on the relative positions of the plates of the casing and the plates of the body. The transducer also includes detectors connected to the plates of the body and of the casing. The detectors are arranged to measure the capacitance of each of the capacitors and to provide, on the basis of this measurement, electrical signals indicative of the forces and the moments applied to the movable member.

Claims

1. A transducer having six degrees of freedom, for converting the forces and moments applied to a movable member, particularly to the movable arm of a robot, into electrical signals, said transducer comprising

a rigid body of substantially cylindrical form intended to be connected to the said movable member, said body having a lateral surface which comprises a first and a second axial portion;

a respective set of four metal plates provided on each of said first and second axial portions of said body, the plates of each set being equi-angularly spaced around the body and being arranged diametrically opposite one another in pairs, the generatrices of the said lateral surface which are tangential to each plate carried by the said first axial portion of the said surface, being tangential to a corresponding plate carried by the said second portion;

a rigid casing having a substantially cylindrical inner surface which surrounds the said body;

resilient spacer means resiliently mounting said casing on the said body in such a way that the casing can perform limited displacements with six degrees of freedom with respect to the body;

two substantially semi-cylindrical equi-angularly spaced metal plates provided on the inner surface of said casing, said semi-cylindrical plates being positioned facing the plates carried by the said body in such a way as to define therewith a narrow interspace and to constitute eight capacitors the capacitances of which depend on the relative positions between the plates of the casing and the plates of the body; and

detector means connected to the said capacitors for measuring, in use, the instantaneous values of the capacitance of each of the said capacitors and for providing, on the basis of this measurement, electrical signals indicative of the forces and the moments applied to the said movable member.

2. A transducer according to claim 1, wherein the said lateral surface and the end surfaces of said body each have at least one annular groove formed therein, said resilient spacer means being constituted by toroidal rings of elastomeric material lodged in the said annular grooves of the body and cooperating with the inner surfaces of the casing.

3. A transducer according to claim 1 or 2, wherein said body is provided at each end with at least one radial projection, said casing being formed with a recess in correspondence with each said projection, and the projections extending into said recesses such as to limit the angular displacements of the casing with respect to the body.

4. A transducer according to claim 2, wherein the casing is provided at each end with a wall extending radially from its inner surface and facing towards a corresponding end surface of the body;

the said radial walls of the casing cooperating with the said toroidal rings lodged in the grooves of the said end faces of the body to limit the axial displacements of the casing with respect to the body.

5. A transducer according to claim 4, wherein each of the said two radial walls is constituted by an annular wall.

6. A transducer according to claim 1, wherein the casing constitutes a handle for manual control of the movable arm of a robot during the teaching phase.

7. A transducer according to claim 1, wherein the casing has at its end which, in use, is opposite the movable arm of the robot, means for connecting a working tool thereto.

8. A transducer according to claim 1, wherein the said detector means include:

eight voltage-to-frequency converters each connected to a respective said plate of the said body, said converters having an associated controlling oscillator which is common to all the converters, and each of the said converters providing output signals the voltage of which is proportional to the capacitance of the corresponding said capacitor; and

processor means for processing the signals emitted by said converters to provide signals indicative of the forces and the moments applied to the casing, and therefore to the movable member by means of the said body.