Twisted string transmission

• US 9,574,646 B1
• Filed: 10/23/2013
• Issued: 02/21/2017
• Est. Priority Date: 10/25/2012
• Status: Active Grant

• Current Assignee: X Development LLC (Alphabet Inc.)
• Original Assignee: Redwood Robotics, Inc.
• Inventors: Edsinger, Aaron, Weber, Jeff, Mullins, Philip, Magnusson, Lee
• Primary Examiner(s): Fennema, Robert
• Assistant Examiner(s): Sivanesan, Sivalingam
• Application Number:
  US14/061,668
• Time in Patent Office: 1,217 Days
• Field of Search: 700/275
• US Class Current: 1/1
• CPC Class Codes: F16H 19/0654 using twisting movement of flexible members to modify the axial length of the mechanism
• CPC Class Codes: F16H 21/16 for interconverting rotary motion and reciprocating motion

Abstract

A twisted string transmission system comprises a twisted string actuator, a force sensor, and a controller. The twisted string actuator is for converting a rotational motion into a linear force. The force sensor is for sensing the linear force. The controller is for receiving sensor information regarding the linear force from the force sensor and for providing control information to control the rotational motion based at least in part on the sensor information.

Claims

1. A twisted string transmission system, comprising:

a twisted string actuator for converting a rotational motion into a linear force;

a force sensor for sensing the linear force;

a controller for;

receiving sensor information regarding the linear force from the force sensor; and

providing control information to control the rotational motion based at least in part on the sensor information; and

a block for extending the actuator throw of the twisted string actuator, wherein the block comprises two pulleys and each string of the twisted string actuator is wrapped around a separate pulley and is separately anchored beyond the separate pin such that beyond the pin, strings of the twisted string actuator are untwisted.

2. The twisted string transmission system of claim 1, wherein the controller controls the rotational motion based at least in part on the sensed linear force.

3. The twisted string transmission system of claim 1, wherein the controller controls the rotational motion based at least in part on a model of the relationship between the linear force and a load displacement.

4. The twisted string transmission system of claim 1, further comprising a motor for providing the rotational motion.

5. The twisted string transmission system of claim 1, wherein the force sensor comprises one of the following:

an encoder, a hall-effect sensor, a capacitive sensor, an IR sensor, a strain-gauge sensor, or an LVDT sensor.

6. The twisted string transmission system of claim 1, further comprising a bending member for bending in response to the linear force.

7. The twisted string transmission system of claim 6, wherein the bending member bends with a linear spring constant.

8. The twisted string transmission system of claim 1, further comprising a spring for expanding or contracting in response to the linear force.

9. The twisted string transmission system of claim 1, wherein the twisted string actuator terminates on a stop block.

10. The twisted string transmission system of claim 9, wherein the stop block is connected to a non-rotating output cable.

11. The twisted string transmission system of claim 10, wherein the output cable wraps around a pulley.

12. The twisted string transmission system of claim 1, wherein a string of the twisted string actuator extends into a shaft of a motor, wherein the motor causes the rotational motion.

13. The twisted string transmission system of claim 12, wherein a lubrication is applied inside the shaft.

14. The twisted string transmission system of claim 12, wherein the string extends from both the front and the back of the shaft.

15. The twisted string transmission system of claim 1, wherein the twisted string actuator comprises part of a differential drive transmission.

16. The twisted string transmission system of claim 1, further comprising diagnostics for determining diagnostic information describing a state of the twisted string actuator.

17. The twisted string transmission system of claim 16, wherein the diagnostics recalibrate one or more control parameters of the controller on a periodic basis.

18. A method for a twisted string transmission system, comprising:

receiving sensor information regarding a linear force of a twisted string actuator of the twisted string transmission system from a force sensor;

providing control information to control a rotational motion of the twisted string actuator based at least in part on the sensor information, wherein the control information controls the rotational motion that is converted into the linear force using the twisted string actuator; and

extending the actuator throw of the twisted string actuator using a block, wherein the block comprises two pulleys and each string of the twisted string actuator is wrapped around a separate pulley and is separately anchored beyond the separate pin such that beyond the pin, strings of the twisted string actuator are untwisted.

19. A computer program product for a twisted string transmission system, the computer program product being embodied in a tangible non-transitory computer readable storage medium and comprising computer instructions for:

receiving sensor information regarding a linear force of a twisted string actuator of the twisted string transmission system from a force sensor;

providing control information to control a rotational motion of the twisted string actuator based at least in part on the sensor information, wherein the control information controls the rotational motion that is converted into the linear force using the twisted string actuator;

determining an output angle of the twisted string actuator from an output angle sensor;

determining a motor angle of the twisted string actuator from a motor angle sensor; and

comparing the output angle to the motor angle over time to determine elongation or breakage of a string of the twisted string actuator.