Stress detection method for force sensor device with multiple axis sensor and force sensor device employing this method

• US 20050229720A1
• Filed: 03/08/2005
• Published: 10/20/2005
• Est. Priority Date: 04/01/2004
• Status: Active Grant

• Current Assignee: Tamagawa Seiki Co., Ltd.
• Original Assignee: Fujitsu Limited, Fujitsu Media Devices Limited (Fujitsu Limited)
• Inventors: Ono, Masaaki, Ishikawa, Hiroshi, Tokunaga, Hiroshi, Miyashita, Tsutomu, Hanazawa, Toshio
• Granted Patent: US 7,320,253 B2
• Time in Patent Office: Days
• US Class Current: 73/862.42
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass
• CPC Class Codes: G01P 21/00 Testing or calibrating of apparatus or devices covered by the preceding groups

Abstract

The present invention provides the stress detection method for force sensor device with multiple axis sensor device and force sensor device employing this method, whose installation angle is arbitrary. The stress detection method includes, first and second force sensors whose detection axes are orthogonal to each other. When the detection axis of first force sensor forms angle θ with direction of detected stress Ax, and the stress component of direction perpendicular to direction of the detected stress Ax is Az, output Apx of the axis direction of first force sensor is found as Apx=α_x (Ax×cos θ+Az×sin θ), and output Apz of the axis direction of the second force sensor is found as Apz=α_z (Ax×sin θ+Az×cos θ), and, when α_x and α_z are detection sensitivity coefficients of first and second force sensors respectively, the detection sensitivity coefficient α_z of second force sensor is set as α_z=α_x tan θ, and the detected stress Ax is found as Ax=(Apx−Apz)/α_x(cos θ−tan θ×sin θ).

Claims

1. A stress detection method for a force sensor device with a multiple axis sensor comprising, as the multiple axis sensor, first and second force sensors the detection axes of which are orthogonal to one other,

wherein, when the detection axis of the first force sensor forms an angle θ

with the axis direction in which detected stress Ax is delivered, and the stress component of an axis direction that is perpendicular to the axis in which the detected stress Ax is delivered is Az,

an output Apx of the axis direction of the first force sensor is found as Apx=α

_x (Ax×

cos θ

+Az×

sin θ

), and

an output Apz of the axis direction of the second force sensor is found as Apz=α

_z (Ax×

sin θ

+Az×

cos θ

), and, when α

_x and α

_z are detection sensitivity coefficients of the first and second force sensors respectively, the detection sensitivity coefficient α

_z of the second force sensor is set as α

_z=α

_x tan θ

, the difference Apx−

Apz between the output Apx and output Apz is found, and the detected stress Ax is found from the difference as Ax=(Apx−

Apz)/α

_x(cos θ

−

tan θ

×

sin θ

).

12. The stress detection method for a force sensor device with a multiple axis sensor according to claim 1, comprising:

prestoring the relationship of correspondence between the output Apz in the axis direction of the second force sensor and the angle θ

;

keeping the force sensor device at rest such that the first axis is in a horizontal direction;

finding the corresponding angle θ

on the basis of the stored relationship of correspondence from the output of the second force sensor thus found; and

storing the angle θ

thus found and finding the detection sensitivity coefficient of the corresponding second force sensor based on the angle θ

thus found.

14. The stress detection method for a force sensor device with a multiple axis sensor according to claim 12 or 13, wherein the storage of the angle θ

thus found can be reset.

2. A stress detection method for a force sensor device with a multiple axis sensor comprising, as the multiple axis sensor:

first and second force sensors the directions of which form an angle Φ

in mutually opposite directions with the direction of a detected stress F1; and

a third force sensor with a detection axis in a direction that is perpendicular to the plane formed with the detection axes of the first and second force sensors,

wherein, when the plane formed with the detection axes of the first and second force sensors forms an angle θ

with the axis direction of the detected stress F1, and the stress component in an axis direction that is perpendicular to the axis in which the detected stress F1 is delivered is F2,

an output Fx of the axis direction of the first force sensor is found as Fx=α

_x×

(F1×

cos Φ

×

cos θ

−

F2×

sin θ

),

an output Fy of an axis direction of the second force sensor is found as Fy=α

_y×

(F1×

cos Φ

×

cos θ

−

F2×

sin θ

),

an output Fz of an axis direction of the third force sensor is found as Fz=α

_z×

(F1×

sin θ

−

F2×

cos θ

), and

the combined output F of the outputs Fx, Fy and Fz is found as F=Fx+Fy−

Fz; and

,

when α

_x, α

_y and α

_z are detection sensitivity coefficients of the first, second, and third force sensors respectively, the detection sensitivity coefficient α

_z of the third force sensor is α

_z=(α

_x+α

_y)×

tan θ

, and the detected stress F1 is then found from the composite output F as F1=F/{(α

_x+α

_y)cos Φ

×

cos θ

−

α

_z×

sin θ

}.

13. The stress detection method for a force sensor device with a multiple axis sensor according to claim 2, comprising:

prestoring the relationship of correspondence between an output Fz of the axis direction of the third force sensor and the angle θ

;

keeping the force sensor device at rest such that the plane formed with the detection axes of the first and second force sensors is placed in a horizontal direction;

finding the corresponding angle θ

on the basis of the stored relationship of correspondence from the output of the third force sensor thus found; and

storing the angle θ

thus found and finding the corresponding detection sensitivity coefficient of the third force sensor based on the angle 0 thus found.

3. A force sensor device with a multiple axis sensor comprising:

first and second force sensors the detection axes of which are mutually orthogonal; and

a circuit for processing the outputs of the first and second force sensors,

wherein, when the detection axis of the first force sensor forms an angle θ

with the axis direction in which the detected stress Ax is delivered and the stress component of an axis direction that is perpendicular to the axis in which the detected stress Ax is delivered is Az, the circuit outputs;

Apx=α

_x (Ax×

cos θ

+Az×

sin θ

) as an output in the axis direction of the first force sensor, and

Apz=α

_z (Ax×

sin θ

+Az×

cos θ

) as an output in the axis direction of the second force sensor,

where α

_x and α

_z are detection sensitivity coefficients of the first and second force sensors respectively and the detection sensitivity coefficient α

_z of the second force sensor is set as α

_z=α

_x tan θ

;

the difference Apx−

Apz between the output Apx and output Apz is found; and

the detected stress Ax is detected from the difference and outputted as Ax=(Apx−

Apz)/α

_x(cos θ

−

tan θ

×

sin θ

).

15. The force sensor device with a multiple axis sensor according to claim 3, comprising:

prestoring the relationship of correspondence between the output Apz of the axis direction of the second force sensor and the angle θ

;

keeping the force sensor device at rest such that the first axis is in a horizontal direction;

finding the corresponding angle θ

on the basis of the stored relationship of correspondence from the output of the second force sensor thus found; and

storing the angle θ

thus found and establishing the detection sensitivity coefficient for the angle θ

thus found.

17. The force sensor device with a multiple axis sensor according to claims 15 and 16, wherein the storage of the angle θ

thus found can be reset.

4. A force sensor device with a multiple axis sensor comprising, as the multiple axis sensor:

first and second force sensors that form an angle Φ

in mutually opposite directions with the axis direction in which the detected stress F1 is delivered; and

a third force sensor with a detection axis in a direction that is perpendicular to the plane formed with the detection axes of the first and second force sensors, the plane formed with the first and second force sensors forming an angle θ

with the axis direction in which the detected stress F1 is delivered; and

a circuit that processes the outputs of the first, second, and third force sensors, such that, when the stress component in an axis direction that is perpendicular to the axis in which the detected stress F1 is delivered is F2, the circuit outputs;

an output Fx of the axis direction of the first force sensor as Fx=α

_x×

(F1×

cos Φ

×

cos θ

−

F2×

sin θ

),

an output Fy of the axis direction of the second force sensor as Fy=α

_y×

(F1×

cos Φ

×

cos θ

−

F2×

sin θ

),

an output Fz of the axis direction of the second force sensor as Fz=α

_z×

(F1×

sin θ

−

F2×

cos θ

), and

the combined output F of the outputs Fx, Fy and Fz as F=Fx+Fy−

Fz; and

,

wherein α

_x, α

_y and α

_z are detection sensitivity coefficients of the first, second, and third force sensors respectively,

the detection sensitivity coefficient α

_z of the third force sensor is α

_z=(α

_x+α

_y)×

tan θ

, and

the detected stress F1 is obtained from the composite output F and outputted as F1=F/{(α

_x+α

_y)cos Φ

×

cos θ

−

α

_z×

sin θ

}.

16. The force sensor device with a multiple axis sensor according to claim 4,

wherein the relationship of correspondence between the output Fz of the axis direction of the third force sensor and the angle θ

is prestored;

the force sensor device is kept in rest such that the plane formed with the detection axes of the first and second force sensors is placed in a horizontal direction;

the corresponding angle θ

is then found on the basis of the stored relationship of correspondence from the output of the third force sensor thus found; and

the angle θ

thus found is stored and the corresponding detection sensitivity coefficient of the third force sensor is established from the angle θ

thus found.

5. A force sensor device that detects stress that is delivered in the detected axis direction comprising:

first and second force sensors that are arranged to form a predetermined angle Φ

in mutually opposite directions with respect to the detected axis direction that run parallel to the sides of the device that form a rectangular shape; and

a third force sensor that has a detection axis that is perpendicular to the plane formed with the detection axes of the first and second force sensors.

6. The force sensor device according to claim 5, wherein the predetermined Φ

is 45°

.

7. A force sensor device that detects stress delivered in a detected axis direction comprising:

a frame portion with outside edges of a rectangular shape;

a weight that is disposed within the frame portion; and

four flexible beams that are arranged in orthogonal axis directions that pass through the center of the weight, the respective one end of which is connected to the weight and the respective other end of which is connected to the frame portion at an inclination that forms a 45°

angle with the outside edge of the frame portion,

wherein each of the four flexible beams comprises a detection element a physical quantity of which varies according to the flexibility of the beams when stress is delivered to the weight.

8. The force sensor device according to claim 7, wherein the detection element a physical quantity of which varies comprises four piezoresistive elements, which are arranged in two mutually orthogonal axis directions that pass through the center of the weight and at the positions where the beams are connected to the frame portion and the weight;

and

the four piezoresistive elements are connected to a Wheatstone bridge.

9. The force sensor device according to claim 8, further comprising:

two sets of the four piezoresistive elements in either one of the two orthogonal axis directions,

wherein the stress of the first axis direction is detected by means of the four piezoresistive elements of one of the two sets and the stress in a direction that is perpendicular to the two orthogonal axis directions is detected by the four piezoresistive elements of the other set.

10. The force sensor device according to claim 9, further comprising:

switch unit that oppositely switch an arrangement in which two resistive elements of four piezoresistive elements arranged in either axis direction of two orthogonal axis directions are connected to the Wheatstone bridge,

wherein the detection of stress in the first axis direction or the detection of stress in the perpendicular direction is rendered possible by means of the connection switching by the switch means.

11. A force sensor device that detects stress delivered in a detected axis direction, comprising:

a frame portion with outside edges of a rectangular shape;

a weight that is disposed within the frame portion;

four flexible beams that are arranged in orthogonal axis directions that pass through the center of the weight, the respective one end of which is connected to the weight and the respective other end of which is connected to the frame portion at an inclination that forms a 45°

angle with the outside edge of the frame portion;

a first electrode portion that is formed on the weight and on each of the four flexible beams; and

an opposing electrode portion that is disposed to face the first electrode portion via an insulator,

wherein the capacitance between the first electrode portion and the opposing electrode portion varies according to the flexibility of the beams when stress is delivered to the weight.