JPH04222472A - Actuator using piezoelectric element and driving method therefor - Google Patents

Abstract

PURPOSE:To provide a rapid, highly accurate, flexible and safe operation well-adapted to restriction by surroundings by controlling a frictional force between a fixed part and a movable body with a frictional force adjusting mechanism having a piezoelectric element. CONSTITUTION:One end of a piezoelectric element for pinching 62 is fixed and the other end is provided with a pushing member 12. On the end of the pushing member 12, a pinching member 11 is so installed that the slanting surface of the pinching member 11 may be joined to the slanting surface of the pushing member 12. Then, a guide board 43 of a movable body 4 is put between the pinching member 11 and a fixed part 2. A frictional force adjusting mechanism is thus obtained. By expanding and contracting the piezoelectric element for pinching 62 with application of voltage, the guide board 43 of the movable body 4 is pinched and thereby a frictional force which works on the movable body 4 is adjusted. In other words, the frictional force which works on the movable body 4 is varied with the voltage applied to the piezoelectric element 62 of the said adjusting mechanism. Accordingly, the fixed driving mode can be obtained by making the frictional force large for fixing the movable body 4 and a free driving mode can be obtained by making the frictional force small for allowing the movable body to move easily.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator for industrial or medical robots, manipulators, etc., and a method for driving the actuator.

0002

[Prior Art] Japanese Patent Application Laid-Open No. 60-601 discloses a technique relating to a method and device for minutely moving a moving object using an impact force.
There is one described in Publication No. 0582.

[0003] The technology shown therein has conventionally been thought that the friction of the guide mechanism would be an obstacle when obtaining highly accurate positioning and movement over minute distances.
The existence of this friction is actively used to apply a minute shock to a moving object that is stationary due to friction, causing a minute movement. (1) The stationary position of the moving object is held by frictional force Therefore, power is not required for holding after positioning is completed.

(2) Since it is a type of self-propelled mechanism, it can perform coarse and fine movements in one.

It has the following characteristics.

As an example of realizing this technology, an actuator using a piezoelectric element as means for generating an impact force is shown in FIG. Further, the movement state and drive voltage pattern for the drive step of the actuator in FIG. 7 are shown in FIGS. 8 and 9, respectively.

The actuator 1 shown in FIG. 7 applies a voltage shown in FIG. 9 to the piezoelectric element 6 to generate a control force greater than the frictional force acting on the moving object 4 due to the interaction between the moving object 4 and the inertial object 7. It is possible to apply an impact force to the movable body 4 to cause it to move minutely.

The driving method will be explained below with reference to FIG.

(2) Keep the piezoelectric element 6 in a constant state.

(2) A voltage is rapidly applied to the piezoelectric element 6 to cause it to expand, thereby moving the movable body 4 and the inertial body 7 in opposite directions.

■ By controlling the acceleration so that the inertia force due to the acceleration of the inertial body 7 is smaller than the static friction force between the movable body 4 and the fixed part 2, the movable body 4 is
, and only the inertial body 7 is pulled back.

■If the movement of the inertial body 7 is suddenly stopped when the element returns to its original length, the inertial body 7 will collide with the moving body 4, and the entire moving part 3 will be affected by static friction. Start a victory movement.

(2) The inertial body 7 moves until it loses the kinetic energy obtained when it is pulled back due to the kinetic friction force, and then stops.

[0014] By repeating the steps from (1) to (2) above several cycles, minute movements or long stroke movements are possible.

[0015]Although the above description is about movement to the left, when moving to the right, the relationship between expansion and contraction of the piezoelectric element 6 may be reversed.

[0016]

The above actuator and drive method may be applied to actuators used in industrial or medical robots, manipulators, or drive devices. The important conditions for actuators in these applications are small size, light weight, and high output/output.
It not only has a high weight ratio, but also high speed, high precision, compliance control, and safety when operating near humans.

[0017] The above-mentioned compliance control is to make a flexible movement suitable for restraint from the environment. It is known that this type of flexibility is required, for example, in tasks such as turning valves with robot arms and assembly tasks.

The skeletal muscles of a living body can be considered as an example of a flexible actuator. This biological actuator can only take two states: contraction and relaxation, but since each joint is made up of one or more pairs of antagonistic muscles to drive the joint, the drive modes for each joint are fixed, increasing, and decreasing. It can have four states: , freedom. "Fixed" is a state where the joint position is held at a fixed position, "increase" and "decrease" are states where the joint position is actively rotated or translated in the positive and negative directions, and "free" is completely flexible and can be controlled from the outside. It is a state of being moved at the mercy of the constraints of the world.

Regarding safety, the above-mentioned fixed and free states are important. For example, if a robot arm is supporting an object, the arm must be firmly fixed with an actuator to prevent the object from falling due to external force, and conversely, if something (such as a human) hits the arm, To avoid this, a free state is required.

However, with the conventional configuration, the magnitude of the frictional force acting on the moving body is fixed at a constant value determined by the mass of the moving body and the friction coefficient of the contact surface on which the moving body is held. . Therefore, in the driving step (■) mentioned above, the frictional force acting on the moving body is an obstacle to movement, and in the driving step (■), if the static frictional force is small, the acceleration that pulls back the inertial body will also be due to it. At the same time, it must be controlled to be small, and the amount of momentum obtained in this drive step also becomes small, resulting in a decrease in the amount of movement in the step (2). As a result of these, high-speed operation is not possible. Although it is possible to obtain the above-mentioned increase and decrease drive modes that move back and forth, it is not possible to arbitrarily switch between fixed and free drive modes in response to various external forces, and it is not possible to arbitrarily switch between fixed and free drive modes in response to various external forces. Safe driving cannot be achieved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a compact and lightweight actuator that is capable of high speed, high precision, flexible and safe operation that adapts to environmental constraints.

[0022]

[Means for Solving the Problems] An actuator using a piezoelectric element of the present invention includes a fixed part, a movable body that is in frictional contact on the fixed part, and a piezoelectric element connected to the movable body. comprises an inertial body coupled in a non-contact state, and an impact force generation mechanism that applies an impact voltage to the piezoelectric element to generate a controlled impact force greater than the frictional force by the piezoelectric element. In an actuator that gives a minute movement to the movable body by impact force, the actuator is provided with a frictional force adjustment mechanism having a piezoelectric element that controls the magnitude of the frictional force between the fixed part and the movable body.

Furthermore, the actuator driving method of the present invention applies an impact force larger than the frictional force to the movable body under the action of frictional force against the fixed part, thereby suppressing minute movements of the movable body. In the method for driving an actuator, the amount of movement of the movable body is controlled by applying the impact force while controlling the friction force.

[0024]

[Operation] With the above means, the frictional force acting on the moving body is changed by the voltage applied to the piezoelectric element of the frictional force adjusting mechanism. This makes it possible to obtain a fixed drive mode in which the movable body is fixed by increasing the frictional force, and a free drive mode in which the movable body is easily moved by an external force by decreasing the frictional force. Furthermore, a drive mode in which frictional force acts between the fixed and free drive modes can be obtained, and these can be controlled arbitrarily during operation.

[0025]

EXAMPLES The present invention will be specifically explained below based on examples.

FIG. 1 shows a perspective view of a specific embodiment of the present invention.
Further, FIG. 2 shows a schematic cross-sectional view thereof.

The actuator 1 of the present invention mainly has a fixed part 2.
and a moving section 3.

The moving unit 3 has a moving object 41 and a moving base 42.
The movable body 4 includes a guide plate 43, and the impact force generating mechanism 5 includes a drive piezoelectric element 61 and an inertial body 7.

A guide groove 9 is provided in the upper part of the fixed part 2, and a friction force adjustment mechanism 8 (see FIG. 3) is incorporated inside.

The moving part 3 has a guide groove 9 provided in the fixed part 2.
The guide plate 43 of the movable part 3 is disposed on the fixed part 2 so as to fit with a small gap, and is movable in the moving direction by being guided by the guide groove 9. The movable base 42 of the movable part 3 and the surface 10 of the guide plate 43 facing the fixed part 2
, and the opposing surface 10 of the fixed part 2 to the movable base 42 and the guide plate 43 may be coated with a lubricant such as a resin coating to reduce the coefficient of friction.

FIG. 3 shows the friction force adjustment mechanism 8. In the figure, one end of the pinch piezoelectric element 62 is fixed inside the fixing part 2, and the pressing member 12 is attached to the other end. Further, a pinch member 11 is provided at the tip of the pressing member 12 so that the oblique sides thereof are joined to each other, and the guide plate 43 of the movable body 4 can be pinched by being sandwiched between the fixing part 2 and the pinch member 11 . Therefore, by applying a voltage to the pinch piezoelectric element 62 and causing it to expand and contract, it is possible to pinch the guide plate 43 of the movable body 4 and adjust the frictional force acting on the movable body 4 . In addition, if the expansion/contraction stroke of the pinch piezoelectric element 62 is insufficient and the adjustment range is affected, the displacement magnification mechanism 1 with a lever action in which a hinge part is formed in the middle of the plate-like part as shown in FIG. 4 is used.
3 may be added.

An example of the driving method of the present invention having the above configuration will be explained below.

The actuator 1 of the present invention applies a drive voltage V1 and a friction adjustment voltage V2 shown in FIG. It operates as follows. FIG. 5 shows the movement state of the actuator for each drive step.

(2) Keep the driving piezoelectric element 61 in a constant state. In this case, the driving voltage V1 is at its minimum and the driving element is in a contracted state. Furthermore, the friction adjustment voltage V2 is also at its minimum, the pinch piezoelectric element 62 is also contracted, and the frictional force is small.

(2) A voltage is rapidly applied to the driving piezoelectric element 61 to cause it to extend, thereby moving the movable body 4 and the inertial body 7 in opposite directions. The pinch piezoelectric element 62 remains in the state of ■, and the movable body 4 moves with small energy.

■When the movement of the moving body 4 is completed, a voltage is applied to the pinch piezoelectric element 62 to stretch it, and the guide plate 43 of the moving body 4 is pinched to increase the frictional force acting on the moving body 4. do.

■ By controlling the acceleration so that the inertia force due to the acceleration of the inertial body 7 is smaller than the static friction force between the movable body 4 and the fixed part 2, the movable body 4 is
prevents the movement of and pulls back only the inertial body. At this time, since the static friction force between the movable body 4 and the fixed part 2 is increased in step (2), the inertial body 7 can be quickly pulled back by greater acceleration.

(2) Just before the drive piezoelectric element 61 returns to its original length, the voltage applied to the pinch piezoelectric element 62 is lowered to reduce the frictional force again.

■ If the movement of the inertial body 7 is suddenly stopped when the drive piezoelectric element 61 returns to its original length, the inertial body 7
collides with the moving body 4, and the entire moving part 3 overcomes the static frictional force and begins to move.

(2) The inertial body 7 moves until it loses the kinetic energy obtained when it is pulled back due to the kinetic friction force, and then stops. ■
Since the inertial body 7 is pulled back with a large acceleration in step , the kinetic energy obtained by the moving part 3 is also large, and
Since the static friction force between the movable body 4 and the fixed part 2 is reduced in step , the amount of movement becomes large.

By repeating steps ① to ① several cycles, minute movements or long stroke movements are possible. Although the length of the fixed part 3 in the moving direction in FIG. 1 is drawn to be slightly longer than the length of the moving part 3, the length of the fixed part 3 can be increased to provide a longer stroke.

[0042]Although the above is an explanation regarding movement to the left, when moving to the right, the relationship between expansion and contraction of the drive piezoelectric element 61 is reversed.
Frictional force adjustment can be performed in exactly the same way as in the case of the left direction.

The actuator of the present invention described above freely controls the friction force acting on the movable body 4 within a certain range by the potential difference ΔV2 of the friction adjustment voltage V2 applied to the pinch piezoelectric element 62 of the friction force adjustment mechanism 8 during operation. Moreover, it can be set instantly, and the movable body 4 can be fixed or set in a free state, so the frictional force can be arbitrarily controlled, making it flexible and safe to adapt to constraints from the environment. It is possible to realize a drive with a high speed. Furthermore, since the piezoelectric element is driven by voltage, the fixed drive mode can be performed with low power.

[0044] Furthermore, since the inertial body 7 can be quickly pulled back in the step (■), one cycle of operation can be completed more quickly, and the amount of movement per cycle is large in the step (■), so it is possible to speed up the movement. At the same time, the frictional force for positioning the moving part 3 can be freely set, and by increasing the frictional force and causing small movements with a large impact force, it is also possible to perform more accurate positioning.

Furthermore, the impact force generating mechanism 5 in FIG. 1 can be made more compact as a whole by using the inertial body 7 as a housing that surrounds the driving piezoelectric element 61, and by using a small piezoelectric element that generates a large force. Furthermore, if necessary, it is also possible to increase the frictional force to make the moving body 4 smaller.

[0046]

[Effects of the Invention] As described above, according to the present invention,
Equipped with a friction force adjustment mechanism, it is possible to realize flexible and safe drive that adapts to restraints from the environment, and allows for high-speed, high-precision operation.Furthermore, since it uses a piezoelectric element, it is small and lightweight, and the voltage It has the great effect of being able to be easily driven with high efficiency by a power source.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an actuator of the present invention.

FIG. 2 is a schematic cross-sectional view of the actuator of the invention.

FIG. 3 is a configuration diagram of a friction force adjustment mechanism.

FIG. 4 is a configuration diagram of a displacement magnifying mechanism.

FIG. 5 is an explanatory diagram of movement states with respect to drive steps.

FIG. 6 is a time chart showing patterns of drive voltage and frictional force adjustment voltage.

FIG. 7 is a front view of a conventional actuator.

FIG. 8 is an explanatory diagram of movement states with respect to drive steps in a conventional example.

FIG. 9 is a drive voltage pattern of a conventional example.

[Explanation of symbols]

1 Actuator 2 Fixed part 3. Moving part 4. Mobile object 5 Impact force generation mechanism 6 Piezoelectric element 61 Drive piezoelectric element 62 Piezoelectric element for pinch 7 Inertial body 8 Frictional force generation mechanism 13 Displacement magnification mechanism

Claims (2)

[Claims] 1. A fixed part, a movable body in frictional contact on the fixed part, an inertial body coupled to the movable body through a piezoelectric element in a non-contact state with the movable body, and the piezoelectric an impact force generation mechanism that applies an impact voltage to the piezoelectric element to generate a controlled impact force greater than the frictional force, and causes the movable body to move minutely by the impact force, An actuator using a piezoelectric element, characterized in that the actuator is equipped with a frictional force adjustment mechanism having a piezoelectric element that controls the magnitude of the frictional force between the fixed part and the movable body. 2. A method for driving an actuator for causing a minute movement of a movable body under the action of a frictional force against a fixed portion by applying an impact force greater than the frictional force to the movable body, the method comprising: A method for driving an actuator, characterized in that the amount of movement of the moving body is controlled by applying the impact force while controlling the frictional force.