JP3147254B2 - Robot movable part positioning method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for positioning a movable portion of a robot such as a hand, a finger or an arm.

[0002]

2. Description of the Related Art Conventionally, an assembling operation by an industrial robot has been achieved by teaching an operation procedure and an operation position in advance and causing the robot to perform an operation according to the teaching procedure and the instruction position. FIG. 1 shows a block diagram of positioning control of a conventional robot device. As shown in the figure, the current position of the fin is obtained from the encoder (E), and the moving speed is calculated from the difference between the current position and the command position.

Among such prior arts, Japanese Patent Laid-Open No. 1-2
When the hand device grips a workpiece, the finger part is placed at a specified position (actual workpiece size> 46087).
(Finger interval), and the workpiece is held at that position. Japanese Patent Laid-Open No. 1-183386 discloses a method for controlling a work by torque.
Is a torque detecting means using a strain gauge or the like, detects the torque applied to the finger portion, and feeds it back to the electric motor.

Further, as a simple method of controlling a work by force, there has been proposed a method or an apparatus in which an electric motor is controlled only by current control as disclosed in Japanese Utility Model Application Laid-Open No. 58558/1983.

[0005]

The work to be rejected has a weight and a size. Therefore, in order for the finger as a rigid body to grasp the work, it cannot be grasped simply by moving to the teaching point, and there is an error in the size of the work or the size differs between works. There is. Therefore, there have been the following problems conventionally.

According to the positioning control block diagram shown in FIG. 1 in the above-mentioned conventional example, in order to carry a work, a target position of a finger is directly input as numerical data in advance, or the finger is actually operated. In this method, the work is grasped and the position of the work is taught, but this input and teaching work takes a very long time. In addition, considering how much overpulse is given to the finger drive system in consideration of the size of the work, it is not considered much whether the work is to be gripped with the target gripping force. Since the finger is actually held by the finger and the operator determines the number of overpulses by relying on intuition, the value varies depending on the operator, is unstable, and requires skill.

Further, in the above method, once a target position is set, the finger portion is always positioned at a fixed position with respect to the work. If the workpiece to be actually gripped is slightly smaller, the target gripping force is not actually generated even if the finger is positioned at the set position, and the workpiece may shift or become worst. In the case of (1), the operation may shift to the next operation without generating any gripping force, that is, without the finger gripping the work. On the other hand, if the work to be actually gripped is slightly larger than the work size set in advance, the finger is positioned at the command position rather than the target gripping force, so that the target It is conceivable that a gripping force larger than the gripping force is generated, and the work is bent or broken. In addition, if a gripper with high rigidity is gripped, more current than expected for the DC servomotor as a drive source will flow, and in the worst case, an overcurrent will occur for a DC servomotor with a small capacity. In such a case, a state in which the DC servo motor itself is broken appears, which is a problem.

On the other hand, when detecting and controlling the gripping force applied to the workpiece, a strain gauge is attached to the finger mechanism and an amplifier for amplifying the output signal of the strain gauge is required. The installation of the gauge complicates the construction of the device, and at the same time makes the device expensive, so that the practicality is reduced. Also, there is a problem that there is no highly reliable strain gauge.

[0009] In addition, with only a simple motor current control,
It is natural that position control cannot be performed, and there is a problem that a large error occurs in the pressing force (gripping force) due to the influence of the friction and rigidity of the mechanism. Therefore, the problem to be solved by the present invention has been proposed in order to solve such a conventional problem, and its purpose is to be able to roughly define the target position, and still ensure that the target It is an object of the present invention to propose a method and an apparatus for positioning a movable part of a robot capable of moving the movable part to a target position.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention comprises an electric motor means for moving a movable part of a robot, and controls a moving position, a moving speed and a driving current of the electric motor means. In the method of positioning the movable portion of the robot by performing the above, coarse position information about a target position is given, the movable portion is positioned at the target position based on the coarse position information, and a positioning operation based on the coarse position information is performed. After the end of the above, a first current value that allows only the movement of the movable portion is given, it is detected that the movable portion has come into contact with the object to be pressed, and a second current value larger than the first current value is detected. Is given to the electric motor means.

According to another aspect of the present invention, there is provided a positioning apparatus including electric motor means for moving a movable portion of a robot, and controlling a moving position, a moving speed, and a driving current of the electric motor means. In a positioning device that positions the movable portion of the robot by doing, means for externally inputting coarse position information about a target position, and means for externally inputting current value data for driving the electric motor means, A positioning control circuit including a speed error detection circuit and a position error detection circuit for positioning the movable portion at the target position based on the coarse position information, a detection unit for detecting a moving state of the movable portion, A current control circuit that performs current amount control based on current value data, and wherein the detection unit moves the movable unit by the positioning control circuit. Upon detecting the zero, characterized by comprising a switching means for switching a driving path to the motor means to the current control circuit from said positioning control circuit.

According to the present invention, the movable portion is first roughly positioned, and thereafter the movable portion is accurately positioned to the target position only by controlling the current.

[0013]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. <Structure> FIG. 2 is a view showing a robot hand mechanism according to the present invention. In FIG. 2, 101 is a servo motor,
Reference numeral 102 denotes a pulse encoder for position detection connected to the servomotor 101; 103, a timing pulley attached to a rotary output shaft of the servomotor; 104, a timing belt; 105, a timing pulley located on the opposite side of the pulley 103; Is a ball screw with both left and right screws cut. 107 and 108 are linear guides,
Reference numerals 109 and 110 denote finger portions, which are movable portions to which nuts (not shown) for the ball screw 106 (not shown) are attached. Reference numerals 111 and 112 denote finger stoppers separately attached to the finger portion and the fixed frame 113. is there. Reference numeral 115 denotes an origin sensor for determining the origin position of the finger portion. Reference numeral 114 denotes a mounting flange for mounting the entire robot hand mechanism to the tip of the industrial robot.

The operation of the robot hand mechanism transmits the rotation output of the servo motor 101 to the timing pulley 103, the timing belt 104, and the timing pulley 105, and rotates the ball screw 106. As a result, the finger portions 109 and 110 can linearly move in a direction away from or approaching the finger portion, and the workpiece can be gripped by these two fingers. Also, the servo motor 101
The positions of the finger portions 109 and 110 can be detected by the pulse encoder 102 attached to the oscilloscope. In addition, the position origin of the finger parts 109 and 110 is
The origin sensor 115 can be set as a reference. When the finger portions 109 and 110 move away from each other, before the finger 109 contacts the frame 113, the stopper 112 of the finger 110 and the frame 11
The third stopper 111 comes into contact with the stopper.

FIG. 3 shows a hardware configuration diagram of a control device for realizing the present method. Reference numeral 201 denotes a central processing unit (CPU) for realizing control; 202, a non-volatile memory (ROM) which is connected to the CPU 201 via a bus and includes a series of control processing algorithm programs and a man-machine interface program; It is a power-backed-up memory (RAM) capable of storing data. Reference numeral 204 denotes a current value counter connected to the pulse encoder 102 connected to the servo motor 101 and capable of counting the current position of the servo motor. Reference numeral 208 denotes a D / A converter connected to the servo motor through a torque amplifier 209, which can output an analog current instruction to the torque amplifier 209 according to an instruction from the CPU 201. Reference numeral 206 denotes an I / O interface for taking information of the origin sensor 115 into the CPU 201. Reference numeral 211 denotes an external teaching device 212 and a CP.
It is a communication interface connecting U. 202,
203, 204, 206, 208, 211 are all connected to the CPU 201 by a bus 213. <First Embodiment> FIG. 4 shows a first embodiment of the present invention and is a control block diagram relating to a gripping force control method of a robot hand mechanism. FIG. 4 is composed of two loops: a positioning control loop (shown by a solid frame in the figure) and a gripping force control loop (shown by a broken frame in the figure). The positioning control loop is a loop for positioning the finger at the “preparation position”, and the gripping force control loop is a loop for controlling the gripping force generated by the finger after the finger is placed at the preparation position. Positioning to the standby position is explained first positioning control loop.

In the figure, a command position register 1 is a register for storing a target command position for gripping a target work. This command position is a position where there is some margin for the size of the target work, that is, a position there. This is a position where the servomotor, which is the driving source of the finger, is operated to a position where there is a certain distance between the target work and the finger when positioned, before shifting to the actual work gripping operation. This is the target command position in the preparation stage of. The target command position 1 is output to the adder 2. The adder 2 obtains a position deviation between the target command position 1 and the current position of the finger unit, and outputs the position deviation to the position loop gain multiplier 3. The position loop gain multiplier 3 calculates a target moving speed by multiplying the position deviation by a predetermined control gain, and outputs the target moving speed to the adder 4. The adder 4 calculates a speed deviation between the input target moving speed and the current moving speed 14 of the finger unit, and outputs the result to the speed loop gain multiplier 5. The speed loop gain multiplier 5
Multiply the input speed deviation by a predetermined control gain,
The target command current is output to the adder 7. The adder 7 obtains a current deviation between the input target command current and the current command current currently being output to the servomotor 9, and outputs this to the torque amplifier 8. The torque amplifier 8 amplifies the input current deviation, outputs the amplified current deviation to the servo motor 9 as a command current. The servo motor 9 is driven by the input command current, generates torque, and opens and closes the finger mechanical mechanisms 109 and 110 to perform positioning. The encoder 102 detects the current position of the finger part,
A signal corresponding to the rotation of the servo motor 10 is output to the current position counter 204, and the current position counter 204 calculates a current position based on a signal from the encoder 102,
The current position. The output of the current position counter 12 is set to the current speed through the differentiator 13. These are conventional positioning control loops.

With this positioning control loop, the finger portion is positioned at a preparation position as a preparation operation for gripping the target work. When the finger is positioned at the preparation position, there is a certain distance between the finger portion and the target work to be gripped. Therefore, teaching work for accurate positioning as in the past is not required, and the teaching operation is simplified. Gripping force control Next, the operation for fingers actually grip the object work is performed as follows.

After the fingers are positioned at the preparatory positions, the loop changeover switch 6 is switched from the positioning control loop side (position b in the figure) to the gripping force control loop (position a). At this time, the command gripping force switch 19 is initially set to the first
It is connected to the command gripping force side (position c). Then, the first command gripping force is set, and the gripping force / torque calculating unit 18 is set.
Output to

The gripping force / torque calculating unit 18 has a converter for converting a commanded gripping force into a torque (current) value. When a commanded gripping force is input, a torque (current) value required for the commanded gripping force is calculated. Output as torque (current) value. Generally, a servomotor generates torque proportionally to a command current value, and naturally, the torque and the force generated by the torque are in a proportional relationship. Things are always in a proportional relationship. Therefore, a simple conversion function is prepared in the gripping force / torque calculation unit 18.

The first command gripping force is determined by a gripping force torque calculator 18.
When it is input to the adder 7, it is converted into a torque (current) value by the conversion function and output to the adder 7 through the loop changeover switch 6 as a command value. Then, constant current value control is performed by a current control loop (a loop returning from the torque amplifier 8 to the adder 7) to generate a constant torque in the servo motor 9, operate the hand mechanical mechanism, and bring the finger into contact with the target work. .

Here, the first command gripping force will be described. After the gripping force / torque calculation unit 18, the command current value has an area where the finger unit does not operate when the command current value is small due to the inherent sliding resistance of the hand mechanism mechanism 11. A value equal to or more than a current value that overcomes the sliding resistance and allows the finger to actually operate is set as a command current value. Invert this value,
It is set in the form of a first command gripping force.

The finger portion of the hand mechanism operates in the direction of gripping the target work in response to the first commanded gripping force, and when the finger portion actually contacts the target work, the command gripping force switch 19 is turned on. 2 command gripping force (d position)
Switch to side. The timing of switching the switch 19 from the position c to the position d is the time when the rotation speed of the motor becomes zero after the loop switching switch 6 is switched from the positioning control loop to the gripping force control side. This speed monitoring is performed by the speed monitor 20, and when the current speed becomes speed = 0, it is determined that the finger portion has contacted the target work, and the command gripping force switch 19 is set to the second command gripping force side. It is to switch.

Then, when the switch is switched to the second command gripping force 17 side, the second command gripping force is output to the gripping / torque calculating section 18 and the command torque (corresponding to the second command gripping force) is converted by a conversion function. The current value is converted to a current value and output to the adder 7 through the loop changeover switch 6 as a command value.
Then, the constant current value control is performed by the current control loop, a constant torque is generated in the servo motor 101, the hand mechanical mechanism is operated, and the finger portion can achieve the target gripping force on the target work.

In the first embodiment, the form of gripping force instruction is used. However, since it is a constant current value control, a method of directly inputting a command current value corresponding to a target gripping force from the beginning to the current control loop, Alternatively, there is a method of giving an instruction in the form of torque. Here, in order to hold the target workpiece with the target gripping force by the finger portion, the reason for controlling in two stages, such as the first commanded gripping force and the second commanded gripping force, is that the command that will correspond to the target gripping force is used. When the value is given at a time, since the positioning is performed at the above-described preparation position so that there is a gap between the target work and the finger portion, depending on the distance, the actual work may be applied to the work when the target work is actually gripped. The gripping force may change greatly,
Considering that a collision may occur, the gripping force instantly applied to the target work becomes a very large gripping force with respect to the target gripping force, which has a bad effect on the target work,
In other words, it is deformed, broken, flies without being able to be gripped, and the generated gripping force varies. Therefore, the finger portion is operated stably and reliably by the first command gripping force 16 so that the gripping force at the time of collision does not significantly change (settles down to a constant value) without considering the interval with the target work. Command value and contact (collision)
Even when there is variation in the gripping force generated when
Command values are set so that those values do not exceed the target gripping force, and thereby the finger portion is brought into contact with the target work. From the state where the finger and the target workpiece are in contact with each other, the gripping force generated with respect to the command current value increases in proportion to the command current value. A grip force is obtained.

FIG. 5 shows an example in which a command value corresponding to the target gripping force is given at one time, and FIG. 6 shows an example of the command value (current) and the generated gripping force according to the present invention. As shown in FIG. 6, it can be seen that the method of the present embodiment produces a small gripping force at the time of contact and a small fluctuation range. Next, FIG.
The gripping process of the first embodiment will be described with reference to FIGS.

FIG. 7 is a flowchart showing the overall operation of moving a robot hand mechanism by a robot arm (not shown) and transporting a work. In step S1, the robot arm moves and positions the target work to be gripped by the robot hand mechanism to a position where it can be actually gripped. Next, in step S2, the operation shifts to an operation in which the finger portion of the robot hand grips the target work. In step S3, when the gripping operation is completed, the robot arm is moved and positioned by the robot arm to the mounting position of the target work. Next, step S4
Then, the robot hand performs a work release operation for assembling the target work. Then, if the operation is continued, the operation returns to the first operation, and if not, the operation ends (step S5).

FIG. 8 is a diagram showing the process of the execution unit of the finger gripping operation in step S2 of FIG.
FIG. STEP1 in FIG. 8 corresponds to steps S11 to S13 in FIG. First, a target position and a target speed are set in order for the finger to move to a position where the target work has some margin (steps S11 and S12), and the finger is moved and positioned to the target position (step S11). S1
3).

When the finger portion is positioned near the work in STEP 1 of FIG. 8, the operation then proceeds to STEP 2 in which the finger portion actually grips the target work from the vicinity of the work. First, a command value is given to the servomotor to drive the finger unit. This corresponds to step S in FIG.
14 is a first command gripping force set. The method of determining the first command gripping force is a command value (current value or gripping force etc) at which the finger portion can move stably and reliably.

As an example, FIG. 10 shows the relationship between the command current value and the displacement of the finger portion. From FIG. 10 and FIG. 11, the command current value is 150 m for the mechanism used here.
Since it is understood that the finger portion is stably and reliably displaced from about A, the first command value is 150 mA.
Is set. In step S15 of FIG. 9, the switch is switched from the positioning control loop to the gripping force control loop. In step S16, the first command value is given to the servomotor, and the finger moves in the workpiece gripping direction stably and reliably. In step S17, the current speed is monitored to determine whether or not the finger portion has contacted the target work, and whether or not the current speed is 0 is determined. If the section is moving, the first command value continues to be given. If the current speed becomes "0", it is determined that the finger section has contacted the target work, and STEP 3 in FIG. 8 and step S18 in FIG.
Proceed to.

Step 3 in FIG. 8 specifically corresponds to steps S18 to S21 in FIG.
At P3, a command current value of a target gripping force for gripping the target work is given. First, in step S18, a second command gripping force (target gripping force) is applied to the target work. Set the command current value. The method of determining the second command gripping force is created in advance by assuming a state in which the finger portion and the workpiece are in contact with each other, and it is confirmed how much gripping force is generated with respect to the command current value. FIG. 11 is an example of plotting how the gripping force generated when the command current value is gradually increased from the state where the finger portion is in contact with the workpiece is changed for this purpose. . Thereby, in the second command gripping force set, the relationship with the command current value actually given can be understood.

Next, in step S19, the switch 19 is switched from the first commanded gripping force to the second commanded gripping force. Then, in step S20, the second command value is given to the servomotor from the state where the finger portion is in contact with the target work, and the target work is reliably gripped with the target gripping force by the second instruction gripping force operation. Move the finger in the direction.

In step S21, it is confirmed whether gripping has been completed, and the flowchart of FIG. 9 is skipped while maintaining the gripping force. Then, the process proceeds to step S3 in FIG. Then, the robot hand is moved by the robot arm to a position where the grasped target work is to be assembled, and the operation proceeds to the operation of releasing the work in STEP 4 of FIG.

When the robot hand is performing a gripping operation in step S2 in FIG. 7, especially in STEP2 and STEP3 in FIG. 9, the command position register 1 in FIG. In step 4 in FIGS. 7 and 8, the operation of substituting the current position into the commanded position is extracted by the finger movement command based on the position command, and the switch 6 is switched in a state where the two values match, and the positioning control is performed. Change to the system, perform normal position control, and move the finger to a position where the work can be released. <Second Embodiment> In the gripping operation flowchart of FIG. 9 of the first embodiment, the first gripping operation in step S16 is an example in which the finger is controlled to move with a constant current value only. A second embodiment for further increasing the reliability of the first gripping operation is shown in the flowchart of FIG. FIG. 12 is a flowchart showing step S16 in the flowchart of FIG.
Is written as a detailed flowchart of the section.

In step S31, first, a preset command lower limit value is set as an initial value, and in step S32, a current is supplied to the servomotor 101 via a torque amplifier. In step S33, it is checked whether the servo motor 101 has not moved due to the friction of the movement guide of the finger portion or the ball screw (that is, whether or not the speed is 0). To continue to supply current to the servo motor. If it has not moved in step S33, it is checked in step S34 whether or not the current command value has exceeded a preset command upper limit value. If it has, the process ends, and the process proceeds to step S17 in FIG. . If the value does not exceed the upper limit in step S34, the process proceeds to step S35, where a preset increase value is added to the current command value, and the process returns to step S36 to execute the above-described contents again. <Application> A case where the above-described pressing method with a constant force is applied to an origin search operation will be described.

FIG. 13 shows a flowchart of the origin finding operation. In this flowchart, STEPA is replaced with STEPB at the time of the gripping operation of the first and second embodiments.
Corresponds to STEP3, and has exactly the same operation as the constant force pressing method. According to the flowchart of FIG. 13, a description will be given using a robot hand mechanism diagram (FIG. 2) and a control block diagram (FIG. 4).

First, before performing the home search operation, FIG.
In this control block, the changeover switch 6 is connected to the position b and connected to the positioning control system. In FIG. 13, when the origin search operation is started, the first command force is set in the gripping force control loop of FIG. 12 in step S31, the switch 19 is connected to the position c, and the switch 6 is connected to the position a in step S32. Switch to gripping force control system.

At steps S33 and S34, the command force is continuously output until the speed becomes zero by the speed monitor 20 while controlling the output. In the operations of steps S33 and S34, the robot hand mechanism (FIG. 2)
The finger portions 109 and 110 move away from each other, and the stopper 112 attached to the finger 110 and the stopper 111 attached to the fixed frame 113 come into contact with each other (STEPA).

Next, in step S35, the second command force is set, and in step S36, the switch 19 is switched.
In steps S37 and S38, the second command force larger than the first command force is output-controlled to the servomotor, and the process proceeds to the next step at the timing when the torque of the servomotor is completely transmitted to the hand mechanism. Step S37, Step S3
In the state of No. 8, the robot hand mechanism (FIG. 2) is in a state where the stopper 111 and the stopper 112 abut with a constant force without variation (STEPB).

Further, in step S39, the STE of FIG.
Connect P6 to position b and switch to positioning control system. At this time, the value of the current position from the counter 204 is substituted into the command position register. In step S40, the small movement amount is continuously added to the command position register 1, and the servo motor is rotated so as to be the reverse of the previous movement method. In step S41, steps S4 and S4 are performed until the Z-phase signal of the pulse encoder connected to the rotating servomotor (one pulse signal per one rotation of the servomotor) is detected.
When the Z-phase signal is detected, the current value counter 12 shown in FIG. 4 is cleared in step S42, the servo motor is stopped, and the origin search operation is completed (STEPC). ).

When this constant force pressing method is applied to the origin search operation of the robot hand or the robot arm, the movable part is pressed with an accurate force, the reproducibility of the deformation of the transmission part is increased, and the origin sensor is eliminated. This has the effect of reducing costs. <Other Modifications> The present invention is not limited to the above three embodiments, and various modifications are possible.

For example, in the example of the origin finding operation of the third embodiment, the method of gradually increasing the command value shown in FIG. 12 in the second embodiment is performed as the operation of step S33 in FIG. The reliability of the home search operation can be further improved. Further, the above embodiment has been described by taking the robot hand as an example, but the present invention can be applied to any robot having a concept of a target position, such as a robot arm.

[0042]

As described above, according to the method and the apparatus for positioning the movable part of the robot according to the present invention, after the coarse positioning by the control system capable of performing the coarse positioning, the torque control by the current control is performed to perform the final control. It can move to the target position accurately. Further, in the torque control system, the first command value is given, and after the movement of the movable portion becomes zero, a second command value larger than the first command value is further given to the motor means. It is possible to approach the target position with an accurate force, and for example, there is an effect that the pressing target can be pressed accurately.

Further, by increasing the first command value in a stepwise manner while confirming the movement, there is an effect that the pressing can be realized more reliably.

[Brief description of the drawings]

FIG. 1 is a control block diagram of a conventional positioning circuit.

FIG. 2 is a diagram showing a robot hand mechanism to which the positioning method of the present invention is applied.

FIG. 3 is a hardware configuration diagram of a control device according to the embodiment.

FIG. 4 is a block diagram of a control device according to the embodiment.

FIG. 5 is a diagram showing a temporal change of a command value and a generated gripping force in the related art.

FIG. 6 is a diagram showing a change over time of a command value and a generated gripping force in the present embodiment.

FIG. 7 is a flowchart of the overall operation of the embodiment.

FIG. 8 illustrates a finger gripping process.

FIG. 9 is a flowchart of a finger gripping operation.

FIG. 10 is a diagram illustrating finger portion displacement with respect to a command current.

FIG. 11 is a diagram showing a command current and a gripping force from a pressing portion contact state.

FIG. 12 is a flowchart of a gripping operation in the second embodiment.

FIG. 13 is a flowchart when the present invention is applied to an origin finding operation.

Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) B25J 3/00-3/10 B25J 9/10-9/22 B25J 13/00-13/08 B25J 19/02-19 / 06

Claims (4)

(57) [Claims] 1. An electric motor means for moving a movable part of a robot, wherein a moving position of the electric motor means,
The robot speed can be controlled by controlling the moving speed and drive current.
In the method for positioning a moving part , coarse position information about a target position is given, and the movable part is positioned at the target position based on the coarse position information. After the positioning operation based on the coarse position information is completed,
A first current value that allows only the movement of the movable portion is provided, and it is detected that the movable portion has come into contact with an object to be pressed, and a second current value larger than the first current value is supplied to the electric motor.
A method for positioning a movable part of a robot, which is provided to a motor means . 2. When the movement of the movable part is not recognized ,
2. The method according to claim 1, wherein the first current value is gradually increased. 3. A method for gradually increasing the first current value.
The case, the method of positioning the movable portion of the robot according to claim 2, characterized in that stopping the increase up to the limit value. 4. An electric motor means for moving a movable portion of the robot, wherein a moving position of the electric motor means,
The robot speed can be controlled by controlling the moving speed and drive current.
In a positioning device for positioning a moving part, a means for externally inputting coarse position information about a target position; a means for externally inputting current value data for driving the electric motor means; A positioning control circuit including a speed error detection circuit and a position error detection circuit for positioning the movable section at the target position based on the current value data; A current control circuit for controlling the amount of current through the positioning control circuit, and when the detection means detects that the movement of the movable section by the positioning control circuit is substantially zero, a driving path from the positioning control circuit to the current control circuit A positioning unit for a movable part of a robot, comprising: