JP2770459B2 - Manufacturing equipment for piezoelectric actuators - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for manufacturing a piezoelectric actuator that can be used, for example, in a fuel injection device of an internal combustion engine for a vehicle.

[Conventional technology]

A piezoelectric actuator using a piezoelectric element made of laminated ceramics or the like is described in, for example, JP-A-61-43266. Also in this prior art, a means such as a disc spring for applying a compressive load to the piezoelectric element in advance is provided, and the load is reduced.
By operating in the linear region of the characteristic curve of the amount of strain, variation in characteristics is prevented.

A typical piezoelectric actuator according to the prior art has a structure as shown in FIG. A cap nut 104 is engaged with a screw portion 103 of a housing 102 that accommodates the laminated piezoelectric element 101, thereby attaching a cap 105, and a spacer 107 supported by the cap 105 via a ball 106 forms a piezoelectric element. It is in contact with the element 101. The lower end of the piezoelectric element 101 is supported by a piston 108, which is urged by a suitable spring 109 to preload the piezoelectric element 101. The displacement of the piston 108 due to the expansion and contraction of the piezoelectric element 101 is taken out by the rod 110.

[Problems to be solved by the invention]

In general, a piezoelectric element has an extremely small displacement of about several tens of μm with respect to an applied voltage within a range in which it can be actually used. When using stacked piezoelectric elements,
As described in the above-mentioned JP-A-61-43266, there is a gap between the element plates due to surface roughness, etc., so that there is a non-linear relationship between the terminal voltage of the element and the displacement. Create a positive relationship. Therefore, a large preload is applied to the piezoelectric element by using a disc spring or the like. However, if an excessively large preload is applied, the piezoelectric element is likely to be damaged due to fatigue, so that an appropriate initial stress is generated. like,
Strict management is required.

However, simply using a disc spring or the like may not be able to accurately generate an optimum preload due to manufacturing errors or variations in characteristics.

Accordingly, an object of the present invention is to provide a manufacturing apparatus for a piezoelectric actuator that performs assembling while managing a preload applied to a piezoelectric element accurately to a predetermined value.

[Means for solving the problem]

The apparatus for manufacturing a piezoelectric actuator according to the present invention includes means for supporting an actuator case including a housing and a cap accommodating the stacked piezoelectric elements at a predetermined position, and the cap in a displacement axis direction of the piezoelectric element. Means for applying a load via the load and maintaining the state, means for measuring the generated voltage of the piezoelectric element and comparing the measured voltage with a preset target voltage, and calculating the difference between the generated voltage of the piezoelectric element and the target voltage. Means for changing the magnitude of the load applied to the piezoelectric element until the load becomes equal to or less than a set value, and while the load applied to the piezoelectric element is held when the voltage difference becomes equal to or less than the set value, Means for fixing the cap to the housing.

[Action]

Since the present invention is constituted by the above means, first, the case of the actuator including the housing and the cap accommodating the stacked piezoelectric elements is placed at a predetermined position of the manufacturing apparatus in a temporarily assembled state. . Next, means for applying a load in the displacement axis direction of the piezoelectric element is urged, and the load acts on the piezoelectric element via the cap. for that reason,
Since the piezoelectric element generates a voltage corresponding to the applied load, it is extracted and compared with a preset target voltage. When the difference between the generated voltage and the target voltage is equal to or larger than the set value, the magnitude of the load is changed so that the difference is adjusted to be equal to or smaller than the set value. When the difference between the voltages becomes equal to or less than the set value, it is when the applied load substantially matches the predetermined value, and the cap is fixed to the housing while maintaining the state, and the assembly of the piezoelectric actuator is performed. Complete.

〔Example〕

FIG. 1 conceptually shows an embodiment of the present invention, in which PZ indicates a piezoelectric actuator which is a workpiece,
As a partial structure, 1 is a laminated piezoelectric element that is displaced in the axial direction when a voltage is applied, 2 is a piston that supports the lower end of the piezoelectric element 1, and 3 is a displacement of the piston 2 caused by expansion and contraction of the piezoelectric element 1. A rod 4 supports a piston 2 from below and generates a compressive force. A housing 5 supports the compressive force of the spring 4 and serves as a case of the piezoelectric element 1. A cap for holding a compressive force, a spacer 7 for supporting the upper end of the piezoelectric element 1, and a ball 8 for applying a load to the center of the axis of the piezoelectric element are shown. The ball seat is formed on the surface of the cap 6 and the spacer 7 as a part of a concave spherical surface having substantially the same diameter as the ball 8,
These form a spherical joint. Reference numeral 9 denotes a connection portion formed by caulking the housing 5 and the cap 6.

A device for manufacturing a piezoelectric actuator PZ is generally M
In the drawing, 10 is a roller for caulking, 11 is a fixed seat of the main body of the manufacturing apparatus M which is also a support base of the piezoelectric actuator PZ, and 12 is a pair of fixing the actuator PZ to the fixed seat 11. , A movable portion for applying a load to the piezoelectric element 1, 13 is a ball screw for moving the movable portion 12 up and down, 14 is a DC servo motor 15 which is a driving source for rotating a screw spindle 13a of the ball screw 13. And a coupling for coupling the spindle 13a with the spindle 13a. Note that 1
Reference numeral 6 denotes a guide shaft supported by a part of the fixed seat 11, which stops the rotation of the movable portion 12 and guides the movable portion 12 so that it can move only in the vertical direction. Reference numerals 17 and 18 denote lead wires derived from the pole plates of the piezoelectric element 1.

The components from the roller 10 to the shaft 16 constitute the actuator PZ while applying an appropriate preload to the piezoelectric element 1.
Is a work head unit WH of an apparatus M for manufacturing a device, 20 is a charge amplifier that charges (integrates) a charge generated by the piezoelectric element 1 to which a load is applied to a capacitor, converts the charge into a voltage and outputs the voltage, and 21 is a charge amplifier. differential increase width unit for Zohaba the difference between the target voltage E _c corresponding to the setting load and the voltage E _s output from 20, 22 enter the rotation angle of the voltage E _r and DC servo motor 15 which is Zohaba servo amplifier for outputting a voltage E _d for rotating the servo motor 15 to a position corresponding to the target voltage E _c as, 23 Zohaba power (in this case current) required for the servo motor 15 is rotated The device, specifically a power transistor amplifier.

FIG. 4 is a front view showing the entire caulking apparatus including the work head WH of the manufacturing apparatus M, and FIG. 5 is a plan view thereof. FIG. 6 is a detailed view of the work head section WH. Next, the structure of the caulking device will be described with reference to FIGS.

The caulking device holds the above-mentioned piezoelectric actuator PZ at a fixed position, and a work head WH for caulking while applying a load, and a swing for bringing the roller 10 as a caulking tool into contact with the case of the piezoelectric actuator PZ. Arm 3
0, a motor 31 for rotating the roller 10, a fixed shaft 32 which is a rotation axis of the swing arm, a swing arm 30
A motor 33 as a drive source for rotating the fixed shaft 32 as a center, a worm 34 for reducing the rotation of the motor, a worm wheel 35, and a housing 5 and a cap 6 which are the case of the piezoelectric actuator PZ. Collet chucks 36 and 37 for holding, motor as drive source for tightening and loosening collet chucks
38, a column 39 to which the work head WH is attached, a base 40 of the main body of the manufacturing apparatus M, and the like.

Next, the detailed structure of the work head WH will be described with reference to FIG. 41a and 41b are a pair of upper and lower rotatable shafts on the same axis having collet chucks 36 and 37 for grasping the case of the piezoelectric actuator PZ, and 42 and 43 are tapered portions and screws for tightening the collet chucks 36 and 37. Gears having portions 44 and 45 (the screw portions 44 and 45 are oppositely threaded to each other), and 46 is a gear that always meshes with the gears 42 and 43 to rotate the actuator PZ. It is mounted on a rotating shaft 48 via an electromagnetic clutch 47. 49 is the fourth
These gears transmit torque from a motor 38, which is a drive source for operating the collet chucks 36 and 37 shown in the figure.

Also, 50 is a disk provided with splines on the outer diameter side, 51
Is a locking shaft that fits into a spline of the disk 50 to prevent the rotation of the shaft 41, 52 is an eccentric cam for pushing the locking shaft 51 in the axial direction, 53 is a rotating shaft of the roller 10, and 54 is a roller. A toothed belt for transmitting a rotational force from a motor 31 which is a driving source for rotating, 55 is a gear attached to the rotating shaft 53 so as to engage with a toothed belt 54, and 56 is a movable part 12 This is a bush provided on the guide shaft 16 that serves as a guide when moving in the vertical direction. The piezoelectric actuator PZ shown in FIG. 6 has a slightly different structure from that shown in FIG. 1, and the piezoelectric element PZ is directly provided by the cap 6 without providing the spacers 7 and the balls 8. The upper end of the piezoelectric actuator PZ is pressed, but as described above, the piezoelectric actuator PZ which is the workpiece in the present invention is not limited to the one shown in the figure.

Next, the state of the device before the piezoelectric actuator PZ as a workpiece is attached will be described with reference to FIGS. 4 and 5. FIG. Roller 10 is in its original operational position, position A in FIG. Further, since the servomotor 15 is at the original position, the movable portion 12 is lifted upward in FIG. 4, and is stationary at a position where the workpiece can be mounted. In the above state, the piezoelectric actuator PZ as a workpiece is temporarily assembled and inserted into the collet chucks 36 and 37.

When the start button of the machine is pressed, the piezoelectric element 1 is moved
Servo motor 12 to the voltage E _s generated by a load applied through the shaft 41a has reached the target voltage E _c
15 rotates, and the movable part 12 moved downward by the ball screw 13 compresses the workpiece. Thereby, the cap 6 overlaps the housing 5 more deeply, and the piezoelectric element 1
Gap is also eliminated. This state is continued from the point O on the characteristic curve indicating the voltage generated by the piezoelectric element 1 in FIG. 2 to the point C which is a predetermined position after passing the bent portion and moving to the linear portion. . In point C, the voltage generated E _s reaches the target voltage E _c, load or stress has a P _c. Further, the displacement amount S of the movable portion 12 indicating the change in length of the piezoelectric element 1 reaches the point C 'on the characteristic curve of the lower half shown in Figure 2, the displacement amount at this time is S _c. When the target voltage E _c and the generated voltage E _s is equal, the servo motor stops the rotation,
Maintain the rotation angle. In this state, the rotation of the shaft 41ab is stopped, and after the electromagnetic clutch 47 is turned on, the motor 38 rotates by a predetermined angle, the gears 42 and 43 are rotated by the gear 46, and the collet chucks 36 and Tighten 37.

When the collet chucks 36 and 37 are tightened, the electromagnetic clutch 4
7 turns OFF and the rotation stop is removed. Next, the motor 33 rotates by a predetermined angle, and the swing arm 30 moves from the position A to the position B
Rotate to the position. The motor 31
Starts rotating continuously, and rotates the roller 10 via the belt 54. When the roller 10 comes to the position B, the cap 5 of the piezoelectric actuator PZ is swaged so as to form a joint 9 with the housing 5 of the case. Accordingly, the piezoelectric element 1 is assembled with the optimum preload (or stress) _Pc shown in FIG. 2 applied. Caulking is performed over the entire circumference of the workpiece by rotating the workpiece by the shafts 41a and 41b. When removing the assembled piezoelectric actuator PZ, the process is the reverse of the above operation.

This operation is shown by a flowchart in the seventh part.
FIG. Although the contents are clear and need not be explained, an electronic control unit having a microprocessor can be used to automatically or partially perform such a procedure.

〔The invention's effect〕

According to the present invention, by the means as described above, the operating characteristics can be accurately matched with the predetermined ones, so that a product having no variation in the strict sense can be obtained, and by applying the initial load of the optimum value to the piezoelectric element, In addition, while maintaining linear operation characteristics, it is possible to minimize damage due to fatigue.

[Brief description of the drawings]

FIG. 1 is a partial sectional view conceptually showing an embodiment of the present invention, FIG. 2 is a diagram showing characteristics of a piezoelectric element, FIG. 3 is a longitudinal sectional view showing a conventional example of an actuator, FIG. FIG. 5 is a front sectional view specifically showing an apparatus according to the present invention, FIG. 5 is a plan view thereof, FIG. 6 is a sectional view showing a part of FIG.
FIG. 5 is a flowchart showing the operation of the embodiment apparatus. 1 ... piezoelectric element, 4 ... spring, 5 ... housing, 6 ... cap, 7 ... spacer, 8 ... ball,
9 ... caulked joint, 10 ... roller, 11 ... fixed seat, 12
…… Movable part, 13… Ball screw, 14… Coupling,
15 …… DC servo motor, 16 …… Guide shaft, 17,18 …… Lead wire, 20 …… Charge amplifier, 21 …… Differential amplifier, 22
…… Servo amplifier, 23 …… Power transistor amplifier,
30 ... Swing arm, 31 ... Motor, 32 ... Fixed shaft, 33 ... Motor, 35 ... Worm wheel, 36,37
…… Collet chuck, 38 …… Motor, 39 …… Column,
40 …… Base, 41a, 41b …… Shaft, 42,43 …… Gears,
44, 45 Screw part, 47 Electromagnetic clutch, 48 Rotating shaft, 50 Disk, 51 Locking shaft, 53 Roller shaft, 54
... toothed belt, 55 ... gear, 56 ... bush, 101 ...
... Piezoelectric element, 103 ... Screw part, 109 ... Spring, PZ ... Piezoelectric actuator, WH ... Work head, M ... Actuator manufacturing equipment.

Claims (1)

(57) [Claims] 1. A means for supporting a case of an actuator comprising a housing and a cap accommodating a laminated piezoelectric element at a predetermined position, and applying a load via the cap in a displacement axis direction of the piezoelectric element. Means for maintaining the state of the piezoelectric element, means for measuring the generated voltage of the piezoelectric element and comparing the measured voltage with a preset target voltage, and until the difference between the generated voltage of the piezoelectric element and the target voltage becomes equal to or less than a set value. Means for changing the magnitude of the load applied to the piezoelectric element, and the housing with respect to the housing while holding the load applied to the piezoelectric element when the voltage difference is equal to or less than a set value. Means for fixing a cap, the apparatus for manufacturing a piezoelectric actuator.