Electricity: motive power systems – Constant motor current – load and/or torque control
Reexamination Certificate
1999-08-05
2002-02-12
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Constant motor current, load and/or torque control
C318S799000, C318S560000, C074S089230, C074S424710
Reexamination Certificate
active
06346788
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an actuator which can convey a workpiece, etc., for example, under the displacing action of the moving member and the controlling device therefor.
BACKGROUND ART
The actuator has been conventionally used for such a purpose as conveying a workpiece. As shown in
FIG. 18
, this actuator
200
comprises an elongate guide base
201
having a rectangular-shaped cross section; a feed screw shaft
202
both ends whereof are supported by bearing blocks (not shown) so that it can be freely rotated, and whereto the rotation drive force of the drive source (not shown) is transmitted; and a moving member
203
wherein a threaded hole engaging the feed screw shaft
202
is formed as a through-hole, and which is moved in both directions along the longitudinal axis of the guide base
201
under the rotating action of the feed screw shaft
202
.
By providing balls
204
between the guide base
201
and the moving member
203
, this actuator
200
is configured so that the moving member
203
can be smoothly moved in both directions under the rolling action of the balls
204
.
However, with the actuator
200
according to the prior art, when, for example, the thread of the feed screw shaft
202
is worn out, resulting in the linear accuracy for the moving member
203
being lowered, or the feed screw shaft
202
is to be replaced with other feed screw shaft having a different diameter, or other driving force transmission member such as a ball screw shaft, the feed screw shaft
202
, moving member
203
, etc., which form a unit, must be integrally replaced, which makes the replacement operation cumbersome. In addition, not only the feed screw shaft
202
but also the moving member
203
must be replaced, and thus a problem of the cost being increased arises.
Also, with the actuator
200
according to the prior art, when the user intends to use the actuator, meeting specifications different from the normal ones to suit to the operating environment, it is difficult to reassemble the actuator
200
to the desired configuration after disassembling, and the reassembling operation to provide the desired configuration is extremely cumbersome, and thus a problem of the cost rising is caused.
Conventionally, a motor-operated actuator
300
as shown in
FIG. 19
, for example, is known. The motor-operated actuator
300
as shown in
FIG. 19
is formed to be elongate along the longitudinal axis, comprising a frame
320
provided with a set of substantially parallel guide rails
318
a
and
318
b
, and a moving member
330
which is displaced along the longitudinal axis of the frame
320
under the guide by the guide rails
318
a
and
318
b.
In a concavity
321
defined in the frame
320
, a ball screw shaft
316
is supported along the longitudinal axis, and to a moving member
330
is fixed a bearing block
341
wherein a threaded hole (not shown) engaging the ball screw shaft
316
is formed. In addition, the motor-operated actuator
300
comprises a supporting block
342
which is fixed to one end portion of the frame
320
and supports the ball screw shaft
316
so that it can be freely rotated, and a brushless motor
322
fixed to the other end of the frame
320
and constituting the driving section for rotation-driving the ball screw shaft
316
.
With the motor-operated actuator
300
configured as above, when the brushless motor
322
is driven by supplying the power to the brushless motor
322
, the rotation drive force of the rotor (not shown) of the brushless motor
322
is transmitted to the ball screw shaft
316
, resulting in the ball screw shaft
316
being rotation-driven in the set direction.
As the ball screw shaft
316
is rotation-driven, the moving member
330
is smoothly and linearly displaced along the guide rails
318
a
and
318
b
through the bearing block
341
engaged with the ball screw shaft
316
, and thus the workpiece (not shown) loaded on the moving member
330
can be conveyed.
The numerals
310
a
and
310
b
denote stoppers fixed to one end and the other end of the frame
320
, respectively, limiting the movable range for the moving member
330
.
However, for a conventional motor-operated actuator
300
as described above, it has been desired that, when the workpiece loaded on the moving member
330
is conveyed along the frame
320
, the torque for the drive source be limited for such a purpose as slowing down the movement of the moving member
330
in such a case as that when a foreign matter or other is sandwiched between the moving member
330
and the stopper
310
a
or
310
b
at either end of the frame
320
, or when the moving member
330
is struck against the stopper
310
a
or
310
b
at either end of the frame
320
.
This is also true when the motor-operated actuator
300
is installed vertically so that the moving member
330
is displaced in a vertical direction, and when the moving member
330
is displaced downward, the lowering speed is increased by the rotation drive force of the drive source and the weight of the workpiece itself, thus it has been required to allow no foreign matter or other to be sandwiched between the moving member
330
and the stopper
310
a
or
310
b.
Thus, as a controlling device for a conventional motor-operated actuator
300
, a friction plate (not shown) or other is provided between the drive source and the ball screw shaft
316
so as to serve as a torque limiter, and when an excessive load is impressed, the friction plate is caused to slip so that an excessive drive force is prevented from being applied to the moving member
330
, thus torque control of the drive source being performed.
However, with the conventional method as stated above, the tightening force for the torque limiter must be preset at a desired value before the drive source is assembled, and in such a case as that when the weight of the workpiece itself is to be changed due to the change of the workpiece to be loaded, it is difficult to change the torque limit value for the torque limiter, thus a problem of the degree of freedom of changing the torque limit value being absent has been presented.
The present invention is intended to offer an actuator and a controlling device therefor which allows only the driving force transmission shaft to be replaced conveniently and inexpensively, and reassembled conveniently to suit to the operating environment, yet allows the torque limit value for the rotation drive source to be easily set and changed.
DISCLOSURE OF THE PRESENT INVENTION
With the actuator according to the present invention, an opening which allows the driving force transmission shaft to be inserted from the direction perpendicular to the axis thereof is formed in the moving block, and thus assembling and maintenance operations for the driving force transmission shaft can be made with convenience.
Further, with the controlling device for the actuator according to the present invention, the level of the manipulated variable control signal which controls the rotational speed of the rotation drive source to the speed based on the generated speed pattern is level-limited to the level of the torque limit value signal, and on the basis of the level-limited manipulated variable control signal, the amount of current supplied to the rotation drive source for the actuator is controlled, which results in the torque for the rotation drive source being controlled to the level of the torque limit limit value signal.
Therefore, the torque for the rotation drive source is controlled on the basis of the torque limit value signal, and the torque limit value signal can be easily set, thus, the torque setting for the rotation drive source can be easily changed to suit to the operating conditions, which allows the torque to be set at an optimum value for the workpiece conditions.
REFERENCES:
patent: 4656726 (1987-04-01), Suzuki et al.
patent: 5263113 (1993-11-01), Naitoh et al.
patent: 5445045 (1995-08-01), Nagai et al.
patent: 5469215 (1995-11-01), Nashiki
patent: 5499547 (1996-03-01), Nagai et al.
patent: 5676016 (19
Morikawa Fumio
Nagai Shigekazu
Shiomi Hiroyuki
Duda Rina
Nappi Robert E.
SMC Kabushiki Kaisha
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