JP3115889B2 - Linear actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention generally relates to a linear actuator used in the FA market such as an assembly line, and more specifically, mainly relates to a stepping motor. The present invention relates to a linear actuator which is a driving source, on which an end effector can be placed, and which moves a moving body guided in a linear direction by a driving force generated by the stepping motor.

[Prior Art] Conventionally, as a drive control method of a linear actuator used in the FA market such as an assembly line, a closed loop control method using a DC motor and an open loop method using a stepping motor have been adopted.

Among these drive control methods, in order to reduce the cost of the linear actuator, the latter open-loop control method using a stepping motor is used.

On the other hand, a moving body of a linear actuator to which a driving force generated by these motors is transmitted is provided with an end effector according to a use purpose of a linear actuator such as a hand for conveying a work.

FIG. 7 shows a block diagram of a conventional linear actuator control device. A stepping instruction signal input from an external control device 3 (for example, a program sequencer) to the linear actuator control device 1 is transmitted to an interface circuit 4. After being converted to an appropriate level, it is input to the arithmetic processing circuit 5.

A series of movement position coordinates are stored in advance in the arithmetic processing circuit 5 by the teaching device 8, and a predetermined number of drive pulses are sequentially sent to the motor excitation current control circuit 6 in accordance with the stepping command.

The motor excitation current control circuit 6 generates a predetermined excitation pattern, and a stepping motor 9 as a drive source so as to obtain a driving force with a sufficient margin to avoid step-out during operation.
To control the exciting current flowing through the power supply.

The driving force generated by the stepping motor 9 is transmitted via an appropriate transmission means so that the moving body 11 performs a linear movement, and the end effector 12 mounted on the moving body 11 performs a desired operation of the user. .

Therefore, even if the excitation current is reduced at the stop point of the stepping motor 9 for the purpose of preventing heat generation and saving power, the moving body 11 is controlled so that the step-out phenomenon does not occur during the operation by the end effector 12. The driving force for the final stop position is controlled to be appropriate.

As an example of the work using such a linear actuator, there is a work that performs a work shaping work (for example, a shaping work of an electromagnetic wire or the like) as shown in FIG. 5 during a predetermined transport work process.

In FIG. 5 (a), a jig 17 held by a hand 12 'mounted as an end effector, a base 18b and a tip 18a
When the positioning with the workpiece 18 is completed, the movement of the jig 17 in the X direction is started at a relatively low speed by the linear actuator.

At this time, when the driving force for the final stop position of the moving body is enhanced by the static torque at the stable point of the stepping motor 9 as described above, and an extra force is applied to the work 18 by the shaping operation, FIG.
Since the shaping operation is continued even after the shaping of the distal end portion 18a of the work 18 as shown in FIG. 7, there is an inconvenience that the work 18 is damaged.

Therefore, when the above-mentioned shaping operation is performed using a conventional linear actuator, it is necessary to provide a mechanism for absorbing extra force in the end effector, and as a result, it is necessary to use an expensive linear actuator as the whole system.

[Problems to be Solved by the Invention] The following points can be considered as reasons for such inconvenience.

In a conventional linear actuator using a stepping motor as a drive source, emphasis is placed on securing the stop position of the moving body, and the driving force control for the final stop position of the moving body does not have flexibility.

In order to realize a low cost linear actuator suitable for the shaping operation as described above, it is necessary to add flexibility to the driving force control for the final stop position of the moving body.

Further, it is necessary to additionally have a function of correcting a positional deviation caused by adding flexibility to the driving force control with respect to the final stop position of the moving body.

An object of the present invention is to provide a linear actuator which solves the above-mentioned conventional problems (problems).

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the linear actuator according to claim 1 uses a stepping motor as a drive source and variably controls an exciting current value of the stepping motor. A current control means, and a movable body capable of mounting the end effector and moving to the work object;
In a linear actuator comprising a guide mechanism that enables the moving body to move linearly, and a unit that directly or indirectly transmits the driving force of the stepping motor to the moving body, the driving current control unit controls the stepping motor. The excitation current of the stepping motor is changed in advance according to the load to set the maximum torque of the stepping motor. During the operation, a load exceeding the maximum torque of the stepping motor is applied to the moving body from the work object. When given, the stepping motor is stepped out to regulate the driving force of the moving body in the moving axis direction.

In the linear actuator according to the second aspect,
A configuration is provided in which means for directly or indirectly detecting the position of the moving body is provided to detect a step-out amount of the stepping motor, and to have a function of correcting a position of the moving body at a stop point based on the detected amount. did.

[Operation] When the exciting current is variously changed according to the load in advance by using the exciting current setting means of the stepping motor to set the maximum torque of the stepping motor, the stepping motor which is the driving source of the moving body is set. When a load exceeding the maximum torque is applied, a step-out phenomenon occurs in the stepping motor, so that the work in the moving axis direction of the moving body is performed by driving force to various stop positions set in advance according to the material of the applied work. Can be done properly.

As a result, flexibility is given to the driving force control with respect to the final stop position of the moving body.

The reason why the exciting current is changed according to the load as described above is that various shaping forces are required depending on the material of the work when shaping the work shown in FIG.

Also, when it is desired to correct a positional deviation due to a step-out phenomenon of the stepping motor at a final stop position of the moving body,
A function is also provided for detecting and correcting the amount of deviation by a position detector.

[Example] Hereinafter, the present invention will be described in detail with reference to an example of the present invention shown in FIGS. 1 to 6.

In each figure, the parts corresponding to those of the prior art are denoted by the same reference numerals as in FIG.

FIG. 1 is a block diagram of a linear actuator control device as one embodiment of the present invention. The difference from the configuration of FIG. 7 is that the motor excitation current setting means 7 and the position detector 10 are different from each other.
Is provided.

In the figure, a step instruction signal input from an external control device 3 (for example, a program sequencer) to the linear actuator control device 1 is converted into an appropriate level by an interface circuit 4 and then input to an arithmetic processing circuit 5.

A series of movement position coordinates are stored in advance in the arithmetic processing circuit 5 by the teaching device 8.
A predetermined number of drive pulses are sequentially sent to the motor excitation current control circuit 6.

The motor excitation current control circuit 6 generates a predetermined excitation pattern, and a stepping motor 9 of a driving source so that a driving force having a sufficient margin can be obtained in order to avoid disengagement during operation.
To control the exciting current flowing through the power supply.

The driving force generated by the stepping motor 9 is transmitted via an appropriate transmission means so that the moving body 11 moves linearly. On the other hand, the feedback signal from the position detector 10 to the arithmetic processing circuit 5 is also taken into consideration, and the teaching device is used. 8 is positioned at a predetermined position taught and stored.

After the positioning is completed, a user's desired work is performed by the end effector 12 mounted on the moving body 11.

At this time, the arithmetic processing circuit 5 includes motor excitation current setting means (for example, a code generation switch having a plurality of bits) 7
And a current command is sent to the motor excitation current control circuit 6.

Generally, the maximum static torque characteristic at the stop position of the stepping motor is as shown in FIG. 4, and changes as shown in FIG. 4 depending on the value of the exciting current _IE .

Stepper motor mover (rotor or mover)
When a displacement of △ θ is given from the stable point as a base point, the maximum torque determined by the exciting current _IE is generated. When the displacement is further given, the torque exceeds the unstable point and stops at the next stable point.

That is, when the exciting current I _E = I _1, maximum torque of T = T ₁ to obtain, when the exciting current I _E = I _2, so that the maximum torque of T = T ₂ is obtained.

FIG. 2 shows a first example of a schematic configuration of a linear actuator using a stepping motor having such characteristics as a drive source.

In the figure, a wire 16 is wound as a transmission means for transmitting a driving force generated by the motor to the moving body 11 around an outer periphery of a driving pulley 14 attached to a rotating shaft of a stepping motor 9 as a driving source. It is connected to the moving body 11.

The other end of the wire 16 is also connected to the moving body 11 via the idler pulley 15.

As a result, the rotating motion generated by the stepping motor 9 is transmitted to the moving body 11, and the moving rod 11 is caused to perform a linear motion with a resolution of approximately 0.01 / step.
The moving body 11 can be moved linearly by a and 13b.

The user mounts an end effector 12 such as a hand suitable for each purpose on the moving body 11 to perform a desired operation.

FIG. 5 shows how the shaping operation is performed using the driving force of the stepping motor, which is the operating force of the linear actuator in the moving axis direction.

The jig 17 gripped by the hand 12 ′ in FIG. 9A starts moving in the X direction toward the work 18 after the predetermined positioning is completed. In this case, the force for moving the moving body in the X direction is
Operating force (thrust).

(B) As shown in the figure, as the shaping of the front end portion 18a of the work progresses, the force opposing the load generated in the R direction is a jig.
The hand 12 ′ holding the 17, that is, the moving body 11 is joined.

At this time, the force in the direction of R applied to the moving body 11 is transmitted to the stepping motor 9 via the wire 16 of the transmission means, but the driving torque of the stepping motor 9 as described above is set to a predetermined maximum torque in advance. Excitation current as regulated
If _IE is set, the force in the R direction causes a step-out of an amount obtained by multiplying the approximate resolution by the number of excitation phases of the stepping motor, and the operating force in the moving axis direction is regulated.

When it is desired to correct the position of the moving body 11 after such work is completed, the amount of step-out during the shaping work is detected using the position detector 10 shown in FIG. 1, and the detected amount is calculated by an arithmetic processing circuit. 5
By feeding back to, the number of drive pulses for moving to the next positioning point is increased or decreased, and the out-of-step amount can be corrected.

The position detector 10 uses an optical encoder as an example,
Although it is possible to indirectly detect the position of the moving body 11 by coupling to the rotating shaft of the stepping motor as shown in FIG. 2, a linear actuator as shown in FIG. By providing a position detector 10 such as a limit switch or an optical sensor at a pre-measured position at the end of the drive mechanism, and after completing the shaping work, once moving the moving body 11 until the position detector 10 operates. The step-out amount can be directly known, and the amount can be corrected similarly to the example of FIG.

In the above embodiment, the case where a rotary motor is used as the stepping motor 9 and the driving force is indirectly transmitted to the moving body 11 using the transmission means has been described. However, the linear stepping motor shown in FIG. A similar effect can be exerted in a linear actuator configured using the same.

In this case, the mover of the motor directly becomes the moving body 11 ',
By making the exciting current supplied to the exciting coil 20 variable, a thrust characteristic similar to that of FIG. 4 can be obtained.

Further, the position detector may be provided with an optical linear encoder in parallel with the stator 19, or a position detector such as a limit switch or an optical sensor at a pre-measured position at one end of the stator 19 as in FIG. May be provided.

[Effects of the Invention] Since the present invention is configured as described above, it has the following excellent effects.

As shown in claim 1, by using the drive current control means,
The exciting current of the stepping motor is changed in advance according to the load to set the maximum torque of the stepping motor. When a load exceeding the limit is applied, the stepping motor is stepped out to regulate the driving force in the moving axis direction of the moving body, so that the final stopping position of the moving body regardless of the fluctuation of the load during work. , The work in the moving axis direction according to the material of the applied work can always be performed appropriately.

According to a second aspect of the present invention, when a means for detecting the position of the moving body and a means for correcting the position at the stop point of the moving body are provided, the stepping motor at the final stop position of the moving body is provided. The position shift due to the step-out phenomenon can be appropriately corrected.

[Brief description of the drawings]

1 to 6 show a specific embodiment of the present invention, wherein FIG. 1 is a block diagram showing a control circuit of a linear actuator according to the present invention, and FIG. 2 is a linear diagram according to the present invention. FIG. 3 is a perspective view showing a first example of a schematic structure of an actuator, FIG. 3 is a perspective view showing a second example of a schematic structure of a linear actuator according to the present invention, FIG. 4 is a characteristic diagram showing a maximum static torque characteristic of a stepping motor, FIG. 5 (a),
(B) is a vertical sectional front view of an essential part for explaining applied work using the linear actuator of the present invention, and FIG. 6 is a perspective view showing a linear stepping motor. FIG. 7 is a block diagram showing a control circuit of a conventional linear actuator. 3: External control device 5: Arithmetic processing circuit 6: Motor excitation current control circuit 7: Motor excitation current setting means 8: Teaching device 9: Stepping motor 10: Position detector 11: Moving body 12: End effector

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ identification symbol FI H02P 8/38 H02P 8/00 R (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 8/00 H02P 7 / 00 101 G05D 3/00

Claims (2)

(57) [Claims] 1. A moving body which uses a stepping motor as a driving source, variably controls an exciting current value of the stepping motor, and a movable body which can mount an end effector and moves to an object to be worked. A linear actuator comprising: a guide mechanism that enables the moving body to move linearly; and a unit that directly or indirectly transmits the driving force of the stepping motor to the moving body. The excitation current of the stepping motor is previously changed according to the load to set the maximum torque of the stepping motor. During the operation, a load exceeding the maximum torque of the stepping motor from the work object is applied to the moving body. When given, the stepping motor loses synchronism and regulates the driving force in the moving axis direction of the moving body. Linear actuator according to claim. 7 2. A function for detecting a step-out amount of the stepping motor by providing means for directly or indirectly detecting a position of the moving body, and correcting a position of the moving body at a stop point based on the detected amount. The linear actuator according to claim 1, wherein the linear actuator is provided.