JP2000069782A - Linear-direction drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable miniaturization of a drive installation portion by downsizing a motor and to enhance the controllability of the motor and reduce vibration and noise by reducing motor drive current. SOLUTION: The drive is provided with a head unit 5 which is supported on guides 13A and 13B installed on a head unit supporting frame 11 so that the head unit can be linearly moved, and a ball screw stem 15 screwed into a nut 16 placed in the head unit 5. Further, a pair of motors 21 and 22 are connected with either end of the ball screw stem 15, respectively, and the pair of the motors 21 and 22 are simultaneously driven to give rotational force to both the ends of the ball screw stem 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a linear driving device mounted on a mounting machine for mounting electronic components on a printed circuit board.

[0002]

2. Description of the Related Art Conventionally, there has been provided a movable member which can move linearly, a feed screw screwed into a nut provided on the movable member, and a motor for driving the feed screw. A linear driving device that moves a movable member by rotating a feed screw is mounted on a machine in various fields.For example, as a machine equipped with this type of linear driving device, electronic components are printed on a printed circuit board. There is a mounting machine to mount.

FIG. 9 schematically shows the structure of a conventional general mounting machine. The mounting machine shown in FIG. 9 includes a head unit a as a movable member, and the head unit a is a head unit supporting frame b. Are held movably in the X-axis direction. X is attached to the head unit support frame b.
A pair of upper and lower guides c extending in the axial direction, a ball screw shaft (feed screw) d arranged parallel to the guide c and rotatably held by the head unit support frame b;
A servo motor e connected to one end of the ball screw shaft d is provided. The head unit a is slidably supported by the guide c, and the nut unit f provided on the head unit a has When the ball screw shaft d is screwed into the ball screw shaft d by the servo motor e.
The head unit is moved in the X-axis direction as is rotated.

[0004] The head unit a is provided with a nozzle for sucking components. The head unit support frame b is held on the mounting machine main body so as to be movable in the Y-axis direction. Then, the electronic component is picked up from the component supply unit by the head unit a and mounted on a printed circuit board.

[0005]

In the above-mentioned conventional driving device, the ball screw shaft d is driven by only one motor e at one end only. When the weight of the head unit a increases (for example, when the head unit is equipped with a large number of nozzles), a large-output motor is required to move the head unit a, and the motor e becomes large, and the motor installation space becomes large. Therefore, it is difficult to make the frame b and the like compact. Also, if a motor with such a large output is used,
Since the motor drive current also increases, a large-capacity driver must be used in the case where the drive current is detected and feedback control of the current is performed. As a result, the resolution of current detection is reduced. Further, there is a problem that vibrations due to torsion and shaking occur during driving of the ball screw by the motor e, and particularly when the resonance frequency is relatively low and resonance occurs in the driving speed range, vibration noise tends to increase.

In view of such circumstances, the present invention makes it possible to reduce the size of the motor, thereby making it possible to reduce the size of the drive device installation portion, and to reduce the motor drive current to improve the controllability of the motor. It is another object of the present invention to provide a linear driving device that is advantageous in reducing vibration noise.

[0007]

According to the present invention, there is provided a movable member supported by a guide extending in a predetermined direction and movable linearly, a feed screw screwed into a nut provided on the movable member. And a motor for driving the feed screw, wherein a pair of motors are connected to both ends of the feed screw, respectively, and the pair of motors are driven at the same time so that both ends of the feed screw are driven. The rotation force is applied to the motor.

According to this device, since the feed screw is driven at both ends by the pair of motors, the expected output of the motor is smaller than that in which the feed screw is driven only at one end by one motor. And the size of the motor can be reduced. The drive current of the motor is also reduced, so that the resolution of current detection when performing current control is prevented from lowering. Further, the resonance frequency of the feed screw is increased by driving both ends.

In the apparatus of the present invention, in addition to the above configuration, a pair of current control means for respectively controlling the drive currents of the pair of motors, a pair of detection means for detecting the speed of each of the motors, Calculating means for calculating a speed difference between the pair of motors based on each output of each detecting means, and correcting a current command value given to each current control unit according to the speed difference calculated by the calculating means, It is preferable to provide a correction means for adjusting the motor drive current so as to reduce the speed difference. In this way, a speed difference between the pair of motors that drive the feed screw is suppressed, and the drive of the feed screw by the pair of motors is effectively performed.

The present invention is also directed to a linear driving device mounted on a mounting machine for mounting an electronic component on a printed circuit board, for example, having a component suction nozzle as a movable member. A head unit that picks up electronic components from the head unit, the head unit is movably held by a head unit support frame, and a guide extending in a predetermined direction is engaged with the head unit support frame by a nut portion provided on the head unit. It is effective that a feed screw and a motor connected to both ends of the feed screw are provided. This is advantageous for downsizing the drive device mounted on the head unit support frame.

[0011]

Embodiments of the present invention will be described with reference to the drawings.

FIGS. 1 and 2 show a mounting machine as an example of a machine provided with the linear driving device of the present invention. In these figures, a conveyor 2 for transporting a printed board is arranged on a base 1 of a mounting machine body, and a printed board 3 is transported on the conveyor 2 and stopped at a predetermined board installation position. Has become. A component supply unit 4 is disposed on the side of the conveyor 2. This part supply unit 4
Has a feeder for supplying electronic components, for example, a multi-row tape feeder 4a.

A head unit 5 is provided above the base 1 as a working member. The head unit 5 picks up an electronic component from a component supply unit and mounts the electronic component on the printed circuit board 3. The head unit 5 includes one or a plurality of suction nozzles 6, and a Z-axis driving mechanism (FIG. (Not shown) and an R-axis drive mechanism (not shown) for rotating the suction nozzle.

The head unit 5 is held by the head unit support frame 11 so as to be movable in the X-axis direction (the direction of the conveyor 2).
Numeral 1 is supported by the mounting machine main body so as to be movable in the Y-axis direction (a direction orthogonal to the X-axis on a horizontal plane). The movement of the head unit support frame 11 in the Y axis direction and the movement of the head unit 5 with respect to the head unit support frame 11 in the X axis direction cause the head unit 5 to move in the X axis direction and the Y axis direction with respect to the mounting machine body. , And can move across the component supply unit 4 and the component mounting unit where the printed circuit board 3 is located.

That is, a pair of linear guides 7A and 7B extending in the Y-axis direction are disposed on the base 1 at a predetermined distance in the X-axis direction.
Further, both ends in the X-axis direction of the head unit support frame 11 formed long in the X-axis direction are supported so as to be movable along the guides 7A and 7B. Further, a ball screw shaft 8 extending in the Y-axis direction in parallel with the guide 7A is disposed below the one end of the head unit support frame 11 and near the guide 7A.

The ball screw shaft 8 is rotatably held with respect to the mounting machine main body, and is screwed to a nut portion (not shown) provided on the head unit support frame 11. A Y-axis servomotor 9 is connected to one end of the shaft 8 via a coupling 10.

The head unit support frame 11 includes:
As shown in FIG. 3, there is provided a pair of upper and lower guides 13A and 13B extending in the X-axis direction.
The head unit 5 is movably held by B, and a ball screw shaft 15 which is a feed screw in the X-axis direction and a pair of X-axis servos for driving the ball screw shaft 15 are provided on the head unit support frame 11. Motors 21 and
2 are arranged.

The ball screw shaft 15 is connected to the two guides 1.
3A and 13B, are rotatably attached to the head unit support frame 11, and are screwed into a nut portion 16 provided in the head unit 5. X-axis servomotors 21 and 22 are connected to both ends of the ball screw shaft via couplings 23 and 24, respectively.

The X-axis servo motors 21 and 22 have encoders 25 and 2 as detecting means for detecting the speed of the motor.
6 is attached.

The configuration of a control system for the X-axis servo motors 21 and 22 will be described with reference to FIG. In the following description, one of the X-axis servo motors 21 and 22 will be referred to as a first motor 21 and the other will be referred to as a second motor 22.

The control system shown in FIG. 4 includes a position command generator 31 and a speed command generator 3 in the control unit 30.
2, a current command generator 33, first and second current controllers 34 and 35, a speed difference calculator 36, and a current command corrector 37. Further, the control unit 30 is provided with the motors 21 and 26 from the encoders 25 and 26, respectively.
A rotation speed detection signal of the rotation speed 22 is sent.

The position command generating means 31 obtains a target position every fixed minute time and outputs a position command value θ _O in accordance with a control pattern set according to the distance of the head unit support frame 11 to the destination. . The speed command generating means 32 compares the position command value θ _O with a position detection value θ ₁ obtained by integrating the speed detection value output from the encoder 25 attached to the first motor 21, to adjust the speed to approach the position of the actually commanded position, and outputs a speed command value omega _O in accordance with the difference therebetween. The current command generating means 33 outputs the speed command value ω
_O is compared with the speed detection value ω ₁ output from the encoder 25, and in order to adjust the motor drive current so that the actual speed approaches the commanded speed, a current command value i _O corresponding to the difference between the two is set. Output.

Each of the current control means 34 and 35 controls the drive current of each of the motors 21 and 22 according to the current command value. Although the details of this current control are omitted from the drawing, for example, the current supplied to the motor is detected, and the detected current value is compared with the current command value so as to match the two. Current feedback control such as controlling supply is performed.

In this case, the first current control means 34 _{supplies the} current command value i _O1 (= i
_O ), the drive current of the first motor 21 is controlled.
The second current control means 35 controls the drive current of the second motor 22 according to the current command value i _O2 corrected by the current command correction means 37.

The speed difference calculating means 36 includes a first motor 2
A speed difference Δω is calculated, which is a difference between the detected speed value ω ₁ output from the encoder 25 attached to ₁ and the detected speed value ω ₂ output from the encoder 26 attached to the second motor 22. Further, the current command correction means 37 gives a deviation to the current command value given to each current control unit according to the speed difference Δω calculated by the speed difference calculation means 36.
The current command value given to the second current control unit is corrected.

The operation of the apparatus of the present embodiment as described above is as follows.
Next, a description will be given.

In the mounting machine, the head unit 5 first picks up an electronic component from the component supply unit, and then mounts the component on the printed board 3 installed at a predetermined position. In such a mounting operation, when the head unit 5 is moved to the component supply unit 4 for component pickup,
When the head unit 5 is moved onto the printed circuit board 3 for mounting components, the head unit support frame 11 is operated in the Y-axis direction by driving the Y-axis servo motor 9, and the X-axis servo motors 21 and 22 are driven. Drives the head unit 5 against the head unit support frame 11.
Is operated in the X-axis direction.

In this case, in this embodiment, a ball screw shaft 15 for moving the head unit 5 in the X-axis direction is used.
Are driven at both ends by a pair of X-axis servo motors 21 and 22, thereby eliminating the need for a high-output motor as in the case of driving by a single motor, and comparing with each motor 21 and 22. It is possible to use a device having a very small size and a low output, and as a result, the drive device can be made compact. In other words, when one large motor is used, a large motor installation space needs to be taken on one side of the ball screw shaft arrangement portion. On the other hand, in the apparatus of this embodiment, two small motors 21 and 22 are used. If there is a small space on each side of the ball screw shaft arrangement portion, the motor can be arranged, and a compact layout can be easily achieved.

Further, as the output of the motor is reduced, the drive current of each of the motors 21 and 22 is reduced.
In the case where the current control means 34 and 35 perform the current feedback control, the resolution of the current detection is prevented from lowering, and the accuracy of the current control is increased. Also, noise generation can be suppressed with a low pulse.

The ball screw shaft 15 is connected to a pair of motors 2.
When both ends are driven by the drive shafts 1 and 22, the resonance frequency of the ball screw shaft 15 becomes higher than when the drive is performed only on one end side. Therefore, the resonance frequency can be increased to such an extent that resonance does not occur in the practical speed range, thereby reducing vibration noise.

By the way, in such a structure of the driving device, the driving speed of the pair of motors 21 and 22 may be the same. In particular, according to the control system shown in FIG.
When a speed difference occurs between the two motors 21 and 22 due to various factors, this can be corrected and the drive of both motors can be adjusted so as to eliminate the speed difference.
This will be described with reference to FIGS.

FIG. 5 shows a model of a three-inertia system composed of each motor and a load when a load (a head unit or the like) is driven using a pair of motors. FIG. 6 is a block diagram showing such a three-inertia system.

Symbols shown in these figures are as follows: T _e1 : generated torque of the first motor T _e2 : generated torque of the second motor T _f1 : shaft torque of the first motor T _f2 : shaft torque of the second motor T _L : Disturbance torque J _M1 : inertia of first motor J _M2 : inertia of second motor J _L : inertia of load θ ₁ : displacement of first motor θ ₂ : displacement of second motor θ _L : displacement of load ω ₁ : first 1 motor speed ω ₂ : second motor speed ω _L : load speed K _F1 : spring constant between first motor and load K _F2 : spring constant between second motor and load C _F1 : first motor and load Viscous friction coefficient C _F2 : Viscous friction coefficient between second motor and load s: Laplace operator

As shown in these figures, the first motor 21
And the inertia J _M1 of the first motor 21 determine the speed ω ₁ of the first motor 21. Similarly, the generated torque T 2 of the second motor 22 is determined by the difference between the generated torque _{Te 1} and the shaft torque T _f1.
The speed ω ₂ of the second motor 22 is determined by the difference between _{e 2} and the shaft torque T _f2 and the inertia J _M2 of the second motor 22. The loads (movable frame 11 and head unit 5) are acted on by shaft torques _Tf1 and _Tf2 and disturbance torque _TL by first and second motors 21 and 22, and these torques _Tf1 and _Tf2. , T _L and the load inertia J _L ,
The load speed ω _L is determined.

Then, the shaft torque T by the first motor 21
_f1 is determined by a difference between the speed ω ₁ of the first motor 21 and the speed ω _L of the load, a spring constant K _F1 between the first motor and the load, and a viscous friction coefficient C _F1 . Similarly, the shaft torque T _f2 of the second motor 22 is determined by the difference between the speed ω ₂ of the second motor 22 and the speed ω _L of the load, and the spring constant K _F2 between the second motor and the load.
And the viscous friction coefficient C _F2 .

Therefore, even if the first and second motors 21 and 22 have the same specifications and the generated torques T _e1 and T _e2 are the same, the first and second motors 21 and 22 are not changed depending on the position of the head unit 5 in the movable frame 11 or the like. Between the motor and load and the second motor
The spring constants K _F1 and K _F2 and the viscous friction coefficients C _F1 and C
If _F2 is different, the speed omega ₁ of the axial torque T _f1, T _f2 motors 21 and 22 in order is changed, omega ₂ in a difference occurs, the motor 2 by the variation of the inertia of the motor to the other
There is a difference between the speeds ω ₁ and ω ₂ of the _first and _second speeds 22.

FIG. 7 is a block diagram in which control by the control system shown in FIG. 4 is added to the block diagram of the inertial system as shown in FIG.

As shown in this figure, in the above control system, the speed command means 32 multiplies the difference between the position command value θ _O and the detected position value θ ₁ by a predetermined position loop gain K _PP to obtain the speed command value ω _O. Is calculated by the current command means 33 on the basis of the difference between the speed command value ω _O and the detected speed value ω ₁ using the speed loop proportional gain K _SP and the speed loop integral gain K _SI to obtain the current command value i. _O is given. And
A current command value i _O1 (= i _O ) is given to the first current control means 34, and a value obtained by multiplying the current command value i _O1 by a torque constant K _T1 of the first motor 21 is a torque T T generated by the first motor 21. _e1
Becomes

On the other hand, by the current command correction unit 37, the first gain K _rm the current command correction value by is applied .DELTA.i _O to the speed difference Δω of the predetermined second motor 21 is calculated, the current command The correction value Δi _O is the current command value i _O
, The current command value i _O2 for the second current control means 34 is obtained. The value obtained by multiplying the current command value i _O2 by the torque constant K _T2 of the second motor 22 is
_Is generated torque _Te2 .

In this manner, the current and the generated torque of the second motor 22 are adjusted according to the speed difference Δω.
When the speed ω ₂ of the motor 22 is lower than the speed ω ₁ of the first motor (when the speed difference Δω is positive), the second motor 22
Is controlled so as to increase the current and the generated torque, so that the speed difference Δω between the two motors 21 and 22 is reduced.

In the above embodiment, a pair of servomotors 21 and 22 are directly connected to both ends of the ball screw shaft 15 in the X-axis direction. However, as shown in FIG. The servo motors 31 and 32 may be connected via a transmission means 33 including pulleys 35 and 36, so that the motor is prevented from protruding outward in the axial direction of the ball screw shaft 15. At the same time, the degree of freedom in layout is increased.

In the above-described embodiment, the present invention is applied to the drive device for rotating the ball screw shaft in the X-axis direction provided on the head unit support frame. However, the Y-axis direction for moving the head unit support frame is used. In other words, the present invention may be applied to the above-mentioned drive device, that is, a pair of Y-axis servomotors may be connected to both ends of the ball screw shaft in the X-axis direction.

Further, the present invention is not limited to the above-described mounting machine, but can be applied to a device in which a movable member is moved by driving a ball screw with a motor, such as a one-axis robot or a quadrature robot.

[0044]

As described above, according to the present invention, a pair of motors are connected to both ends of a feed screw screwed to a nut portion provided on a movable member, and the pair of motors are simultaneously driven so that the feed screw is driven. Since a rotational force is applied to both ends of the motor, a large-output motor is not required unlike the case where a single motor drives the feed screw, so that the motor can be downsized and the motor installation space can be reduced. Can be reduced, and the drive device can be laid out compactly. In addition, since the driving current of the motor decreases as the output of the motor decreases, the resolution of current detection can be prevented from lowering, and the accuracy of current control can be increased. Further, since the resonance frequency of the feed screw is increased by driving both ends, it is advantageous in reducing vibration noise.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an example of a mounting machine to which the present invention is applied.

FIG. 2 is a front view of a portion where the head unit of the mounting machine is supported.

FIG. 3 is a schematic diagram of a head unit driving portion in the mounting machine.

FIG. 4 is a block diagram illustrating a configuration of a control system.

FIG. 5 is an explanatory diagram showing a model of an inertial system.

FIG. 6 is a block diagram of the inertial system.

FIG. 7 is a block diagram in which control by the control system of FIG. 4 is added to the inertial system.

FIG. 8 is a schematic view showing another embodiment of the present invention.

FIG. 9 is a schematic view of a head unit driving portion of a conventional general mounting machine.

[Explanation of symbols]

 5 Head Unit 11 Head Unit Support Frame 15 Ball Screw Shaft 21, 22 Servo Motor 25, 26 Encoder 34 Current Control Means 36 Speed Difference Calculation Means 37 Current Command Correction Means

Continued on the front page F-term (reference) 5E313 AA01 AA11 CC03 EE01 EE02 EE24 EE25 5H303 AA05 BB02 BB07 BB12 CC01 DD01 FF03 HH02 JJ01 KK03 KK17 LL03 5H572 AA14 BB03 BB07 BB10 DD01 EE06 GG01 GG02 GG01 GG02

Claims (3)

[Claims] 1. A movable member supported by a guide extending in a predetermined direction and movable linearly, a feed screw screwed into a nut portion provided on the movable member, and a motor for driving the feed screw A pair of motors are respectively connected to both ends of the feed screw, and the pair of motors are simultaneously driven to apply a rotational force to both ends of the feed screw. A linear drive device characterized in that: 2. A pair of current control means for controlling a drive current of each of the pair of motors, a pair of detection means for detecting the speed of each of the motors, and the pair of current control means based on each output of each of the detection means. Calculating means for calculating the speed difference of the motor; and correcting the current command value given to each of the current control units according to the speed difference calculated by the calculating means to reduce the motor drive current so as to reduce the speed difference. 2. The linear driving apparatus according to claim 1, further comprising a correcting unit for adjusting the driving direction. 3. A linear drive device mounted on a mounting machine for mounting an electronic component on a printed circuit board, wherein the electronic component is picked up from a component supply unit having a nozzle for component suction as a movable member. Equipped with a head unit
The head unit is movably held by the head unit support frame, and the head unit support frame has a guide extending in a predetermined direction, a feed screw screwed to a nut provided on the head unit, and two ends of the feed screw. 3. The linear drive device according to claim 1, wherein a connected motor is provided.