JP2002040358A - Control device for optical scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an optical scanner capable of reducing torsional vibrations and bending vibrations generated at a rotary shaft mounted with a mirror, shortening a mirror positioning time, and further improving positioning accuracy of a laser beam. SOLUTION: To position a mirror at a final angle instructed from a higher rank control unit, a mirror vibration control element 41 removes a natural vibration component from the bending vibration of the rotary shaft to obtain a target angle value signal 21. Moreover, the control device is provided with torsional vibration compensation circuits 33, 34 receiving a current detection signal 31 as an input and negatively feeds back the output to an integral value of a deviation of a detected angle value 22 from the target angle value 21, and thereby controls a value of a motor driving current 29.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an optical scanner device having an angle detecting device and positioning a mirror supported on a rotating shaft around the rotating shaft.

[0002]

2. Description of the Related Art An optical scanner device used in laser marking and laser drilling of a printed circuit board rotates a mirror attached to a rotating shaft by a built-in electric motor and changes the angle of the mirror. A predetermined position on the workpiece is irradiated with laser light output from the laser oscillator.

FIG. 6 is a configuration diagram of a movable section in an optical scanner device. The mirror 11 is attached to one end of the rotating shaft 12. The rotating shaft 12 is supported by bearings 14 and 15, rotates by receiving a driving torque by a moving coil 13 integrated with the rotating shaft 12, and is positioned at a predetermined angle. Hereinafter, the mirror 11, the rotating shaft 12, and the moving coil 13 that rotate integrally are collectively referred to as an optical scanner 1.

The optical scanner 1 is provided with an angle detection sensor (not shown) for detecting a rotation angle of the rotation shaft 12, for example, a variable displacement sensor. The variable capacitance type sensor is configured such that a dielectric flat plate attached to the rotating shaft rotates with the rotating shaft between a pair of fixed pole plates, and the angle of the rotating shaft is the capacitance between the plates. Is detected as an electrical signal. The technology relating to such a variable capacitance type sensor is disclosed in, for example, US Pat. No. 3,517,282.
No. 4,864,295 and JP-A-7-55500.

FIG. 7 is a control block diagram of a conventional optical scanner device. The angle detection signal 22 is negatively fed back to the angle target value signal 21 commanded by the host controller, and the value of the deviation signal 23 in the steady state is set to 0.
3 is integrated by the integration compensation circuit 24. In order to maintain the stability of the servo mechanism, the angle detection signal 22 is input to the proportional compensation circuit 25 and the differential compensation circuit 26, and the sum of the output signals of these circuits is subtracted from the output signal of the integration compensation circuit 24. The control input signal 27 is used. The motor drive circuit 28 supplies the optical scanner 1 with a motor drive current 29 proportional to the control input signal 27. The motor driving current 29 flows through the moving coil 13, and a driving torque proportional to the current value is generated in the moving coil 13.

[0006]

When a hole is formed in a printed circuit board by a laser beam, a positioning error of the laser beam to be processed needs to be about 10 μm or less in order to precisely process the fine circuit pattern. In addition, in order to shorten the processing time, it is required to speed up the movement from one hole to the next hole processing position.
When zero holes are to be formed, it is necessary to set the average moving time between holes to less than 1 ms.

Incidentally, the laser light has an energy distribution and is incident on the mirror 11 with an area spread. For this reason, in order to process a high-quality hole, it is desirable that the mirror 11 be large (having a large area).

However, when the size of the mirror 11 is increased, the torsional vibration and the bending vibration of the rotating shaft 12 are increased, which hinders a high response of the mirror positioning.

First, the effect of torsional vibration will be described. When the size of the mirror 11 increases, the moment of inertia about the rotation axis 12 also increases, so that the natural frequency of torsional vibration in which the rotation axis 12 becomes a torsion spring decreases. The primary mode of the torsional vibration is a torsional vibration having the smallest natural frequency. There is one torsion node in the longitudinal direction of the rotating shaft 12, and both sides sandwiching this node are angularly displaced in opposite phases. In the torsional vibration secondary mode, the natural frequency is the second lowest, and the rotating shaft 1
There are two nodes in the longitudinal direction of No. 2 and the portions on both sides vibrate in opposite phases with respect to the central portion sandwiched between the nodes.

For example, when an angle detection sensor is disposed near a mirror, the nodes of the torsional vibration are located between the angle detection sensor and the moving coil 13 so that the two may have opposite phases. In such a case, in the conventional servo mechanism, the torsional frequency component of the angle detection signal 22 becomes a positive feedback, and the control becomes unstable. A wide control band is desirable in terms of high response of mirror positioning and suppression characteristics of low-frequency disturbance, but the control band is limited by a decrease in natural frequency.

When the node of the torsional vibration overlaps or approaches the position of the sensor, the vibration mode cannot be observed by the angle detection sensor, so that it cannot be controlled and stabilized. The positioning accuracy of the laser beam has decreased.

Next, the effect of bending vibration will be described.
It is desirable that the movable portion of the optical scanner shown in FIG. However, for example, if the mass of the mirror with respect to the two sides in the longitudinal direction receiving the driving torque of the moving coil 13 or the axis of the rotating shaft 12 is different on the left and right, the difference in mass becomes an unbalance weight. Then, due to the inertial force of the unbalance weight accompanying the operation of the optical scanner 1, bending vibration is generated on the rotating shaft 12 with the bearings 14 and 15 as support points. As a result, the mirror 11 vibrates in a direction parallel or perpendicular to the mirror surface. Generally, the optical scanner 1 is not provided with a sensor for detecting bending vibration of the rotating shaft 12 or an actuator for applying a force to the rotating shaft 12 in the bending vibration direction. Also,
In the feedback control by the above conventional servo mechanism,
Once generated, bending vibration cannot be attenuated. For this reason, the positioning accuracy of the laser beam could not be improved.

An object of the present invention is to solve the above-mentioned problems in the prior art, to reduce torsional vibration and bending vibration generated on a rotating shaft on which a mirror is mounted, to shorten a mirror positioning time, and to reduce a laser light beam. An object of the present invention is to provide a control device of an optical scanner device that can further improve positioning accuracy.

[0014]

In order to achieve the above object, the present invention provides an optical scanner device for positioning a mirror supported on a rotating shaft around the rotating shaft based on an angle target value and an angle detection value. And a correction value relating to the torsional vibration of the rotating shaft is added to an integral value of a deviation between the angle target value and the angle detection value.

[0015] In this case, the correction value is calculated by calculating the r of the torsional vibration of the rotating shaft by the driving torque applied to the rotating shaft.
The output value of the transfer function up to the next (where r is a positive integer) angular velocity can be used, and the output value of the transfer function is calculated from the current value supplied to the motor that generates the drive torque. Can be calculated.

Further, in the control device of the optical scanner device for positioning the mirror supported on the rotation axis around the rotation axis based on the angle target value and the detected angle value, the target trajectory is a time function of the position, A specific frequency component is removed from the sum of the target trajectory and a target speed and a target acceleration based on the target trajectory to obtain the angle target value.

In this case, the specific frequency component can be a natural frequency component of bending vibration of the rotating shaft or a natural frequency component of torsional vibration of the rotating shaft.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present invention will be described with respect to torsional vibration. The frequency response (self-compliance) from the driving torque received by the moving coil 13 to the angular displacement of the moving coil 13 is represented by the transfer function G in Equation 1.
(S).

[0019]

(Equation 1) Here, s is a complex variable of Laplace transform, n is a subscripted variable representing the nth mode of torsional vibration (where n is a positive integer), ω _n is the natural angular frequency of the nth mode of torsional vibration, ζ _n
The attenuation coefficient of the torsional vibration n-th order mode, k ₀ is a constant related to the rigid body mode, the k _n is a mode constant of the torsional vibration n-th mode.

Here, paying attention to a specific torsional vibration mode (r-th mode), the transfer function G _r (s) of the _r-th mode included in the second term of the equation (1) is calculated from the driving torque by the moving coil 13. And H _r (s) shown in Expression 3 is a transfer function from the driving torque to the angular velocity of the r-th mode at the position of the moving coil 13.

[0021]

(Equation 2) Since the transfer function H _r (s) represents the response (self-frequency response) at the position where the drive torque acts, the mode constant k _r is positive. Therefore, if the value of the transfer function H _r (s) is negatively fed back to the control input signal 27, the r-th mode can be controlled and attenuated stably.

When the motor drive circuit 28 is of the current control type, the drive torque of the moving coil 13 is normally proportional to the motor drive current 29. Therefore, by measuring the motor drive current 29, the drive torque of the moving coil 13 is measured. I understand. The current detection signal corresponding to the value of the motor drive current 29 is, for example, the motor drive current 29
Through a current detection resistor having a small resistance value (0.1 to several Ω or less), and inputting the voltage between the terminals of the resistor to a differential input type subtraction circuit to obtain an output of the differential input type subtraction circuit. Can be.

Hereinafter, the present invention will be described with reference to the illustrated embodiments. FIG. 1 is a control block diagram of an optical scanner device according to the present invention. Components having the same functions or the same functions as those in FIG. A deviation signal 23 obtained by negatively feeding back the angle detection signal 22 to the angle target value signal 21
Is integrated by the integration compensation circuit 24. In order to maintain the stability of the servo system, the angle detection signal 22 is supplied to the proportional compensation circuit 2.
5 is input to a speed observer 32 described later.

Further, a current detection signal 31 having a magnitude corresponding to the value of the current supplied to the moving coil 13 is input to a speed observer 32 and a primary torsion compensation circuit 33 and a secondary torsion compensation circuit 34 described later. Then, the proportional compensation circuit 25, the speed observer 32, the torsional primary compensation circuit 3
3 and the sum of the output signals of the torsion secondary compensation circuit 34 is subtracted from the output signal of the integration compensation circuit 24 to obtain a control input signal 2
7 is assumed.

Next, the r-th torsion compensation circuit will be described.

By actually measuring the frequency response of the mirror 11, the r-th natural frequency and the damping coefficient can be known. Further, a secondary filter having a frequency response characteristic having the same sign and proportional to Equation 3 (hereinafter referred to as a torsion r-order compensation circuit)
Can be constituted by an electronic circuit.

FIG. 2 is a connection diagram of such a r-th torsion compensation circuit, and includes three operational amplifiers 333 to 335 and 6
It comprises resistors R _{01 to} R ₀₆ and two capacitors C ₀₁ and C ₀₂ . The positive input terminals of the operational amplifiers 333 to 335 are grounded. And the operational amplifier 3
The negative input terminal 33 is connected to one terminal of the resistor _R01 and one terminal of the capacitor _C01 . The output terminal of the operational amplifier 333 is connected to the other terminal of the capacitor _C01 and one terminal of the resistor _R03 . The other terminal of the resistor R ₀₃ is connected to the resistor R ₀₂ , the resistor R ₀₄ , one terminal of the capacitor C ₀₂ , and a negative input terminal of the operational amplifier 334. The output terminal of the operational amplifier 334 is connected to the other terminal of the capacitor _C02 , the other terminal of the resistor _R04 , and one terminal of the resistor _R05 .
Negative input terminal of the operational amplifier 335, the other terminal of the resistor R _05, is connected to one terminal of the resistor R _06. Output terminal of the operational amplifier 335, the other terminal of the resistor R _06, and is connected to the other terminal and the terminal 332 of the resistor R _01. The other terminal of the resistor _R02 is connected to the terminal 33.
1 connected. Further, the resistor _R02 is a variable resistor.

In this circuit, the resistance value R ₀₅ and the resistance value R
₀₆ is equal, the input signal 331 to the output signal 332
The transfer function Gc (s) up to is as shown in Expression 4.

[0029]

(Equation 3) Then, the resistance values R ₀₁ , R ₀₃ , R ₀₄ and the capacitances C ₀₁ , C ₀₂ of the capacitors are represented by the constant term of the denominator polynomial of the equation (4)
Is set to be equal to the constant term of the denominator polynomial of Equation 4 and the coefficient of the primary term of the denominator polynomial of Equation 4 is equal to the coefficient of the primary term of the denominator polynomial of Equation 3.
_r and the damping coefficient ζ _r become equal to the r-th vibration mode.

Therefore, when the current detection signal 31 is input to the terminal 331, the output signal output from the terminal 332 (hereinafter referred to as the output signal 332) is
Is proportional to the angular velocity of the r-th mode at the same position with the same sign. Therefore, by negatively feeding back the output signal 332 to the output signal of the integration compensation circuit 24, the r-th vibration mode can be stabilized, that is, the r-th vibration can be reduced.

In this embodiment, the resistance value R ₀₂ can be set independently of the natural frequency and the damping coefficient.
_{By making 02} a variable resistor, the amplitude of the output signal of the torsional r-order vibration compensation circuit can be adjusted.

The control block diagram shown in FIG. 1 shows a case where the primary torsion compensation circuit 33 and the secondary torsion compensation circuit 34 are provided to stabilize the primary mode and the secondary mode of the torsional vibration. 2 is provided for each mode, and these are connected in parallel with the primary torsion compensation circuit 33, the secondary torsion compensation circuit 34, etc. Can be stabilized.

Next, the speed observer 32 will be described. In the present invention, a velocity observer 32 is provided in place of the conventional differential compensation circuit 26, and the angular velocity of the rigid mode corresponding to the first term of Expression 1 is estimated. Then, the servo system of FIG. 1 is stabilized by negatively feeding back the obtained estimated signal to the output signal of the integration compensation circuit 24.

FIG. 3 is a connection diagram of the speed observer 32, in which two operational amplifiers 324 and 325 and six resistors R
And ₁₁ to R _16, and a capacitor C ₁₁ Prefecture. The positive input terminals of the operational amplifiers 324 and 325 are grounded. Negative input terminal of the operational amplifier 324 is connected to one terminal of one terminal and the capacitor C ₁₁ of the resistors R ₁₁ ~ resistor R _13. The other resistor R ₁₁ is the terminal 3
21 and one terminal of the resistor R _{14, and} the other of the resistor R ₁₂ is connected to the terminal 322. Output terminal of the operational amplifier 324 is connected to the other terminal of the capacitor C _11, to one terminal of the other terminal and the resistor R ₁₅ of the resistor R _13. Negative input terminal of the operational amplifier 325 is connected to one terminal of the other terminal and the resistor R ₁₆ between the resistor R ₁₄ resistor R _15. The output terminal of the operational amplifier 325 is connected to a resistor R ₁₆
Are connected to the other terminal and the terminal 323.

In this circuit, the resistance values R ₁₁ , R ₁₃ , R
_When the values of R ₁₄ and R ₁₅ are set so as to satisfy the relationship of Expression 5, the signals input to the terminals 321 and 322 (hereinafter referred to as input signals 331 and 332) and the signals output from the terminal 323 (hereinafter referred to as input signals 331 and 332). The relationship with the output signal 333 is as shown in Expression 6.

[0036]

(Equation 4) Here, E _i1 (s) is a Laplace transform of the input signal 321 and is a signal obtained by inverting the sign of the angle detection signal 22.
E _i2 (s) is the Laplace transform of the input signal 322 and is the current detection signal 31. E _o (s) is a Laplace transform of the output signal 323 and is an angular velocity estimation signal.

The first-order transfer function of the first and second terms of Equation 6 is
It has a common denominator polynomial, and the constant term 1 / R ₁₃ C ₁₁ is the corner frequency of each transfer function. In accordance with the first term of Equation 6, in the region lower than the corner frequency, the derivative of the angle detection signal is mainly used as the angular velocity estimation signal, and according to the second term of Equation 6, this derivative is used. In a region higher than the point angular frequency, the integration of the current detection signal mainly becomes an angular velocity estimation signal, and the angular velocity of the rigid mode at the position of the moving coil 13 can be accurately estimated.

When the angle detection sensor is arranged at a position distant from the moving coil 13, the angle detection signal in a frequency region near the torsional frequency is shifted with respect to the angular displacement at the position of the moving coil 13.
Therefore, when the angle detection sensor is positioned away from the moving coil 13, so that the corner angular frequency becomes lower than the torsional vibration primary mode, the value of the resistance R ₁₃ and the capacitance C ₁₁ of the capacitor It is desirable to decide. By doing so, the degree to which the torsional frequency component of the angle detection signal is positively fed back can be reduced, so that the stability of the servo system can be ensured even if the servo band is wider than that of the conventional servo system.

Next, an embodiment for suppressing the mirror vibration due to the bending vibration of the rotating shaft will be described.

FIG. 4 is a block diagram of the vibration suppressing element according to the present invention. The target trajectory 411 is a target profile of the rotation angle of the mirror 11.

Here, the target trajectory 411 is represented by α
_MAX is the maximum acceleration, and the shortest time trajectory of one inertial body that performs the maximum acceleration and the maximum deceleration for the same time. Note that L is
This is a stroke from the start of rotation at time 0 to the stop at time T _M. In this case, the acceleration time function α (t),
Time function of velocity v (t) and time function of position x (t)
Are represented by Equations 8 to 10, respectively.

[0042]

(Equation 5) Then, the time function x (t) of the position is set as the target trajectory 411, and the output of the differential element 412 and the output of the second-order differential element 413 are added to the target trajectory 411, and the notch filter 41 is added.
Enter 4 Then, the output signal of the notch filter is set as the angle target value signal 21. Incidentally, a constant of the notch filter, the angular frequency omega _b is equal to the natural angular frequency of the bending vibration of the rotary shaft 12. The constant ζ _{b of the} denominator polynomial and the constant ζ _bn of the numerator polynomial are set so that ζ _b > ζ _bn .

Here, if the Laplace transform of the time function of the target trajectory 411 is X (s) and the Laplace transform of the angle target value signal 21 is R (s), the relationship between X (s) and R (s) is obtained. Has the relationship shown in Expression 11, and the bending frequency component of the rotating shaft 12 is removed by the zero point of the numerator polynomial of the notch filter.

[0044]

(Equation 6) Therefore, when the angle target value signal 21 is input to the feedback control system shown in FIG. 1, the vibration of the mirror accompanying the positioning operation can be suppressed.

Although the notch filter has a phase delay determined by the coefficient of the denominator polynomial, the denominator polynomial of the notch filter is canceled by adding the output of the target trajectory 411, the output of the differential element 412, and the output of the second-order differential element 413. . As a result, the phase lag from the target trajectory 411 to the angle target value signal 21 is eliminated, and the mirror 1
1 can reduce the delay of the positioning operation.

As described above, it is difficult to attenuate the bending vibration once generated by feedback control.
In the present invention, the bending vibration of the rotating shaft 12 is prevented by generating an input to the feedback control system, that is, the angle target value signal 21 by the mirror vibration suppressing element 41.
The positioning error of the laser beam due to the mirror vibration can be reduced.

By the way, the Laplace transform of the target velocity which is the first derivative of the time function of the target trajectory is V (s), and the Laplace transform of the target acceleration which is the second derivative of the time function of the target trajectory is Α (s). Then, Equation 11 can be transformed into Equation 12.

[0048]

(Equation 7) FIG. 5 is a block diagram of the vibration suppressing element according to the present invention, which implements Expression 12. In the figure, gain elements 417 and 418 are notch filters 414
Is a weighting factor determined by the constant of With such a configuration, by weighting and adding the target trajectory (Equation 10), the target speed (Equation 9), and the target acceleration (Equation 8), the notch filter 414 shown in FIG. FIG.
The angle target value signal 21 equivalent to the mirror vibration suppression element shown in FIG.

Here, the vibration suppressing element shown in FIGS. 4 and 5 can be easily realized by a microprocessor. In this case, when the feedback control system in FIG. 1 performs analog control, the present invention can be applied by converting a digital angle target value signal into an analog signal using a DA converter and using it.

Instead of calculating the target trajectory, the target speed, and the target acceleration each time, these time series values are calculated in advance and stored in a memory, and the data stored during the positioning operation is sequentially read. It may be. In this case, if each target value is normalized by the stroke L and stored in the memory, the memory capacity can be reduced.

The operation time T _M may be set in several ways depending on the magnitude of the stroke L.

Further, the target trajectory is not limited to the one represented by Expression 10, and a time waveform that can be differentiated with a rank equal to or higher than the order of the denominator polynomial of the notch filter 414 can be used as the target trajectory.

The angular frequency ω of the notch filter 414
_{When b} is equal to the natural angular frequency of the torsional vibration of the movable portion of the scanner, the torsional vibration can be reduced with a configuration different from that described in the torsional vibration compensation circuit. In this case, the servo mechanism is not limited to the servo mechanism shown in FIG. 1, but may employ the conventional servo mechanism shown in FIG.

[0054]

As described above, according to the present invention,
Since the torsional and bending vibrations of the movable part of the optical scanner are attenuated in a controlled manner, the stability of the servo mechanism can be ensured even when the servo band is wide, and the laser beam can be positioned at high speed and with high accuracy. it can.

Further, since the mirror vibration suppressing element is configured so that there is no phase delay of the input of the angle target value from the target trajectory, the laser beam can be positioned at a high speed.

[Brief description of the drawings]

FIG. 1 is a control block diagram of an optical scanner device according to the present invention.

FIG. 2 is a connection diagram of an r-th torsion compensation circuit according to the present invention.

FIG. 3 is a connection diagram of a speed observer according to the present invention.

FIG. 4 is a block diagram of a vibration suppressing element according to the present invention.

FIG. 5 is another block diagram of the vibration suppressing element according to the present invention.

FIG. 6 is a configuration diagram of a movable unit in the optical scanner device.

FIG. 7 is a control block diagram of a conventional optical scanner device.

[Explanation of symbols]

 Reference Signs List 21 angle target value 22 angle detection value 29 motor drive current 31 current detection signal 33 torsional vibration compensation circuit (primary) 34 torsional vibration compensation circuit (secondary) 41 mirror vibration suppressing element

Continued on the front page (72) Inventor Yoshio Nakajima 502 Kandate-cho, Tsuchiura-shi, Ibaraki Pref. Machinery Research Laboratory, Hitachi Ltd. (72) Inventor Atsushi Sakamoto 502, Kantate-cho, Tsuchiura-shi Ibaraki Pref. (72) Inventor Miyako Okubo 2100 Kamiimaizumi, Ebina City, Kanagawa Prefecture Inside Hitachi Via Mechanics Co., Ltd. (72) Inventor Masahiro Oishi 2100 Kamiimaizumi, Ebina City, Kanagawa Prefecture Inside F-term of Hitachi Via Mechanics Co., Ltd. 2H041 AA12 AB14 AC04 AZ06 2H045 AB44 AB54

Claims (6)

[Claims] 1. A control device for an optical scanner device for positioning a mirror supported on a rotation axis around the rotation axis based on an angle target value and an angle detection value, wherein a deviation between the angle target value and the angle detection value is provided. A controller for adding a correction value relating to torsional vibration of the rotating shaft to the integral value of the optical scanner. 2. The correction value is an output value of a transfer function up to the r-th order (where r is a positive integer) angular velocity of torsional vibration of the rotating shaft due to a driving torque applied to the rotating shaft. The control device for an optical scanner device according to claim 1, wherein: 3. The control device according to claim 1, wherein an output value of the transfer function is calculated from a current value supplied to a motor that generates the driving torque. . 4. A control device for an optical scanner device for positioning a mirror supported on a rotation axis around a rotation axis based on an angle target value and an angle detection value, wherein the target trajectory is a time function of position, A control device for an optical scanner device, wherein a specific frequency component is removed from a sum of the target trajectory and a target speed and a target acceleration based on the target trajectory to obtain the angle target value. 5. The control device for an optical scanner device according to claim 4, wherein the specific frequency component is a natural frequency component of bending vibration of the rotating shaft. 6. The control device for an optical scanner device according to claim 4, wherein the specific frequency component is a natural frequency component of the torsional vibration of the rotating shaft.