# US 10,870,202 B2 · Variable stiffness actuator with electrically modulated stiffness

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- Number: US 10,870,202 B2
- Document ID: US10870202B2
- Status: Granted
- Kind: B2
- Application number: 16/111,072
- Filed: 2018-08-23
- Published: 2019-02-28
- Granted: 2020-12-22
- Earliest claimed: 2017-08-23
- Assignees: Board of Regents, The University of Texas System
- Applicants: Board of Regents, The University of Texas System
- Inventors: Robert D. Gregg; Edgar A. Bolivar; David P. Allen; Walter E. Voit
- Web page: https://patentgrep.com/patent/US10870202B2

## CPC

- B25J 9/1633: {compliant, force, torque control, e.g. combined with position control}
- B25J 9/0009: {Constructional details, e.g. manipulator supports, bases}
- B25J 9/123: {Linear actuators}
- B25J 9/1694: {characterised by use of sensors other than normal servo-feedback from position, speed or acceleration sensors, perception control, multi-sensor controlled systems, sensor fusion}
- B25J 19/068: {Actuating means with variable stiffness}
- B25J: MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES ({manipulators specially adapted for use in surgery A61B34/70; manipulators used in cleaning hollow articles B08B9/04}; manipulators associated with rolling mills B21B39/20; manipulators associated with forging machines B21J13/10; {manipulators associated with picking-up and placing mechanisms B23P19/007}; means for holding wheels or parts thereof B60B30/00; {vehicles with ground-engaging propulsion means, e.g. walking members B62D57/02, B62D57/032; devices for picking-up and depositing articles or materials between conveyors B65G47/90, B65G47/91; manipulators with gripping or holding means for transferring packages B65H67/065}; cranes B66C; {manipulators used in the protection or supervision of pipe-line installations F17D5/00; walking equipment adapted for nuclear steam-generators F22B37/006}; manipulators specially adapted for, or associated with, nuclear reactors G21C; {apparatus used for handling wafers during manufacture or treatment of semiconductor H10P72/50})

## Abstract

A dielectric elastomer system (DES) variable stiffness actuator (VSA) is provided. In an embodiment, the DES VSA includes a variable stiffness module (VSM). The VSM includes a DES that softens when energized and stiffens when unpowered, an outer frame, and an inner frame member. The stiffness of the DES is variable. The outer frame supports the DES and the inner frame member, which is disposed within the DES. The inner frame member is configured to be displaceable with respect to the outer frame. The DES VSA also includes an actuation motor mechanically coupled to the inner frame member that is configured to cause a force to be applied to the inner frame member and the actuation motor is configured to control an equilibrium position of the DES VSA.

## Claims

### Claim 1

A variable stiffness actuator (VSA) comprising:
an input block and an output block;
a plurality of stacked dielectric elastomer system (DES) diaphragm modules positioned between the input block and the output block, each DES diaphragm module including an outer frame, an inner frame, and a variable stiffness membrane spanning between the outer frame and the inner frame, the variable stiffness membrane configured to soften when energized and stiffen when not energized, wherein one of the input block or output block is coupled to the outer frames and another of the input block or output block is coupled to the inner frames; and
an actuator mechanically coupled to the input block, the actuator configured to move the input block in a direction substantially parallel with a stacked direction of the DES diaphragm modules.

### Claim 2 (depends on 1)

The VSA of claim 1, further including a stiffness controller coupled to the plurality of stacked DES diaphragm modules, the stiffness controller configured to adjust the stiffness of the variable stiffness membranes by varying a control voltage applied thereto.

### Claim 3 (depends on 1)

The VSA of claim 1, wherein the stiffness of the variable stiffness membranes is at a maximum stiffness level when not energized.

### Claim 4 (depends on 1)

The VSA of claim 1, wherein the stiffness of the variable stiffness membranes is controlled without aid of a motor.

### Claim 5 (depends on 1)

The VSA of claim 1, wherein a force output of the actuator is measured without separate force sensors.

### Claim 6 (depends on 1)

The VSA of claim 1, wherein the actuator is an actuation motor, and further wherein the input block is coupled to the inner frames and the output block is coupled to the outer frames, and further including a ball screw coupled between the actuation motor and the input block, wherein the actuation motor is configured to drive the ball screw thereby applying a force to the inner frames.

### Claim 7 (depends on 6)

The VSA of claim 6, further including an output point connected to the output block, the output point configured to connect the VSA to a load.

### Claim 8 (depends on 1)

The VSA of claim 1, further including a linear-bearing guide-rod system connecting to a mount of the actuator and configured to constrain an output point of the VSA to linear motion.

### Claim 9 (depends on 1)

The VSA of claim 1, further including a stiffness controller coupled to the plurality of stacked DES diaphragm modules, the stiffness controller configured to adjust the stiffness of the variable stiffness membranes by varying a control voltage applied thereto, wherein the actuation motor, the plurality of stacked DES diaphragm modules, and the stiffness controller are configured such that the equilibrium position of the plurality of stacked DES diaphragm modules and the stiffness of the plurality of stacked DES diaphragm modules are independently controllable.

### Claim 10 (depends on 1)

The VSA of claim 1, wherein an applied stiffness of the plurality of stacked DES diaphragm modules is independent of an applied force to the plurality of stacked DES diaphragm modules.

### Claim 11 (depends on 1)

The VSA of claim 1, wherein the variable stiffness membranes each comprise an elastomer layer, a first compliant electrode layer covering a first surface of the elastomer layer, and a second compliant electrode layer covering a second surface of the elastomer layer, the first and second compliant electrode layers configured to provide a voltage difference across a plane of the elastomer layer, wherein an increasing voltage difference causes an increase in softening of the elastomer layer.

### Claim 12 (depends on 1)

The VSA of claim 1, wherein the plurality of stacked DES diaphragm modules are electrically coupled to a stiffness controller in parallel such that the plurality of stacked DES diaphragm modules charge and discharge together.

### Claim 13 (depends on 1)

The VSA of claim 1, wherein the variable stiffness membranes comprise one of an acrylic elastomer, silicone, a fluorosilicone, a polyurethane, and a natural rubber.

### Claim 14 (depends on 1)

The VSA of claim 1, wherein the variable stiffness membranes comprise Very High Bond (VHB) 4910.

### Claim 15 (depends on 1)

The VSA of claim 1, wherein the inner frames comprise a substantially circular disk.

### Claim 16 (depends on 1)

The VSA of claim 1, wherein the inner frames are situated substantially in a center of the outer frames.

### Claim 17 (depends on 1)

The VSA of claim 1, further including a polyimide film lining edges of the plurality of stacked DES diaphragm modules, thereby reinforcing the plurality of stacked DES diaphragm modules against an electrical field and mechanical stress concentrations that occur near the edges of the plurality of stacked DES diaphragm modules.

### Claim 18 (depends on 1)

The VSA of claim 1, wherein the actuator is an actuation motor.

### Claim 19 (depends on 1)

The VSA of claim 1, wherein the input block is coupled to the inner frames and the output block is coupled to the outer frames.

### Claim 20

A variable stiffness actuator (VSA) comprising:
a plurality of stacked dielectric elastomer system (DES) diaphragm modules, each DES diaphragm module including a variable stiffness membrane comprising a material that will soften when energized and stiffen when not energized;
a stiffness controller connected to the plurality of stacked DES diaphragm modules and configured to control the stiffness of the DES diaphragm modules;
an actuator mechanically coupled to the plurality of stacked DES diaphragm modules and configured to control an equilibrium position of the VSA, the actuator configured to move in a direction substantially parallel with a stacked direction of the DES diaphragm modules; and
a connector connecting the plurality of stacked DES diaphragm modules to a load.

### Claim 21 (depends on 20)

The VSA of claim 20, wherein the actuator is an actuation motor.

### Claim 22

A variable stiffness actuator (VSA) comprising:
a plurality of stacked dielectric elastomer system (DES) diaphragm modules, each DES diaphragm module including a variable stiffness membrane, wherein a first side of each of the variable stiffness membranes is at least partially covered by a first compliant electrode, wherein a second side of each of the variable stiffness membranes is at least partially covered by a second compliant electrode, and wherein each of the variable stiffness membranes is configured to soften when energized with an electric field applied via the first and second compliant electrodes and to become stiffer when unenergized;
a stiffness controller connected to the plurality of stacked DES diaphragm modules, the stiffness controller configured to control the stiffness of the variable stiffness membranes via application of a control voltage thereto;
a ball screw;
an actuator coupled to the ball screw, the actuator configured to adjust an equilibrium position of the VSA by moving in a direction substantially parallel with a stacked direction of the DES diaphragm modules;
an input block configured to mechanically couple the ball screw to one of inner frames or outer frames of the plurality of stacked DES diaphragm modules;
an output block configured to mechanically couple the other of the outer frames or the inner frames of the plurality of stacked DES diaphragm modules to an output connection point, the output connection point configured to receive a load.

### Claim 23 (depends on 22)

The VSA of claim 22, wherein the actuator is an actuation motor.

### Claim 24 (depends on 22)

The VSA of claim 22, wherein the input block is coupled to the inner frames and the output block is coupled to the outer frames.