Stress sensing device, tactile sensor, and grasping apparatus

1. A stress sensing device for sensing a shear force acting in a shear direction and a pressing force perpendicular to the shear direction, the stress sensing device comprising:

a support body including an opening defined by a pair of straight parts perpendicular to a sensing direction of the shear force and parallel to each other;

a support film on the support body and closing the opening, the support film having flexibility;

a first piezoelectric part configured to output an electrical signal by bending, the first piezoelectric part being disposed over the support film and straddling an inside portion and an outside portion of the opening along at least one of the straight parts of the opening as seen in plan view when the support body is viewed from a thickness direction of the support film;

a second piezoelectric part configured to output an electrical signal by bending, the second piezoelectric part being disposed to the inside portion of the opening and set apart from the first piezoelectric part as seen in the plan view; and

an elastic layer covering the first piezoelectric part, the second piezoelectric part, and the support film.

2. The stress sensing device according to claim 1 , wherein

the opening includes a pair of first straight parts and a pair of second straight parts perpendicular to the first straight parts; and

the first piezoelectric parts are disposed respectively along at least one of the first straight parts and at least one of the second straight parts.

3. The stress sensing device according to claim 1 , wherein

the first piezoelectric parts are disposed respectively along each of the pair of straight parts.

4. The stress sensing device according to claim 1 , wherein

the second piezoelectric part is disposed at the center of the opening viewed in the plan view, and

on the support film, support beams are disposed respectively at locations that, when viewed in the plan view, are symmetrically disposed with respect to a line segment which passes through the center of the second piezoelectric part and extends parallel to the sensing direction of the shear force.

5. The stress sensing device according to claim 4 , wherein

the opening is formed in a rectangular shape, and

the support beams are formed on diagonal lines of the opening.

6. The stress sensing device according to claim 4 , wherein

the second piezoelectric part includes a lower electrode layer formed on the support film, a piezoelectric layer formed on top of the lower electrode layer, and a upper electrode layer formed on top of the piezoelectric layer, and

the support beams include a lower electrode line connected to the lower electrode layer, and a upper electrode line connected to the upper electrode layer.

7. A tactile sensor comprising:

a plurality of the stress sensing devices for sensing a shear force acting in a shear direction and a pressing force perpendicular to the shear direction, the stress sensing devices being arranged in an array, each of the stress sensing devices including

a support body including an opening defined by a pair of straight parts perpendicular to a sensing direction of the shear force and parallel to each other,

a support film on the support body and closing the opening, the support film having flexibility,

a first piezoelectric part configured to output an electrical signal by bending, the first piezoelectric part being disposed over the support film and straddling an inside portion and an outside portion of the opening along at least one of the straight parts of the opening as seen in plan view when the support body is viewed from a thickness direction of the support film,

a second piezoelectric part configured to output an electrical signal by bending, the second piezoelectric part being disposed to the inside portion of the opening and set apart from the first piezoelectric part as seen in the plan view, and

an elastic layer covering the first piezoelectric part, the second piezoelectric part, and the support film.

8. The tactile sensor according to claim 7 , wherein

the elastic layer of the stress sensing devices includes regulating grooves between the stress sensing devices adjacent to each other, the regulating grooves regulating transmission of flexion through the elastic layer.

9. A grasping apparatus for grasping an object comprising:

a tactile sensor including a plurality of the stress sensing devices for sensing a shear force acting in a shear direction and a pressing force perpendicular to the shear direction, the stress sensing devices being arranged in an array, each of the stress sensing devices having

a support body including an opening defined by a pair of straight parts perpendicular to a sensing direction of the shear force and parallel to each other,

a support film on the support body and closing the opening, the support film having flexibility,

a first piezoelectric part configured to output an electrical signal by bending, the first piezoelectric part being disposed over the support film and straddling an inside portion and an outside portion of the opening along at least one of the straight parts of the opening as seen in plan view when the support body is viewed from a thickness direction of the support film,

a second piezoelectric part configured to output an electrical signal by bending, the second piezoelectric part being disposed to the inside portion of the opening and set apart from the first piezoelectric part as seen in the plan view, and

an elastic layer covering the first piezoelectric part, the second piezoelectric part, and the support film;

at least one pair of grasp arms configured to grasp the object, the grasp arms having the tactile sensor disposed on a contact face that contacts the object;

a grasp sensing unit configured to sense a slippage state of the object based on the electrical signal output by the tactile sensor; and

a drive control unit configured to control driving of the grasp arms based on the slippage state.