JPS6325324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light deflection device that mechanically moves a mirror.

Mechanical optical deflection devices such as galvanic mirrors have a slow deflection speed but a large deflection angle and high resolution.
For example, Proceedings
of SPIE vol 84 Laser Sbanning Components
and Techiques (1976) and similar vol 53
It has been widely used for a long time, as described in Laser Recording.

Further, the characteristics and driving method of the galvanic mirror are covered in detail in the above-mentioned literature and in the instruction manual of General Scanning.

In many applications you want to get a serrated motion, so
Although a sawtooth motion is considered here, the results can be applied to other motions as appropriate. In general, it is desired to have a deflection that repeats as quickly as possible and has a large temporal effectiveness rate for one cycle of the slope portion where the sawtooth wave is effectively used.

In order to make a sawtooth movement, it is necessary to quickly suppress the vibration that occurs in the retrace section, so the movement of the mirror is detected and fed back to the input, and damping is applied electrically.
Alternatively, vibrations are suppressed by using a stepped signal waveform.

The latter method will be briefly explained using FIG. The horizontal axis of the figure shows the time axis, and the vertical axis shows the deflection angle.
In the figure, the solid line represents the drive signal, and the dotted line represents the movement of the mirror. This drive signal is set in advance so that when the drive signal is applied until time t ₀ , the peak of the overshoot of the mirror movement that follows it will be at the desired deflection angle. Then, at the final time t ₀ of the applied drive signal, two levels of signals are applied to the retrace section of the mirror in order to return the mirror to the starting position. By doing this, the mirror can be moved in a short transition time without causing vibration.

However, even if such a method is adopted, approximately half of the period corresponding to the resonant frequency of the galvanic mirror is required for the transition time to return the mirror to its starting position. Therefore, if you want to ensure a time efficiency of 70% in the slope section of the sawtooth wave, you can only operate the sawtooth wave at a repetition frequency of about 50% to 60% of the resonant frequency at most. The literature listed above indicates that it is practically 30% to 40%.

The resonant frequency of the galvanic mirror cannot be increased that much once the necessary resolution and deflection characteristics such as the deflection angle are determined.In the end, it is important to move the galvanic mirror given the resonant frequency as fast as possible.
As described above, conventionally, driving is limited to a repetition frequency that is less than half of the resonant frequency, and there is a desire to improve this.

In addition, the deflection characteristics of the galvanic mirror are such that as the speed increases, the inductance of the drive coil cannot be ignored.
Shows third-order characteristics. Generally speaking, when it comes to higher-order properties,
The delay becomes large and it is not suitable for high-speed drive. This is also a problem with normal drive methods.

An object of the present invention is to provide a light deflection device that mechanically moves a mirror and is capable of deflecting light at high speed and with a high time efficiency.

In the present invention, the characteristics of the deflection device including the drive circuit are made quadratic, and the effective deflection section is driven by a signal corresponding to the movement of the mirror, and the transient section is driven by a signal consisting of two levels, high and low. Drive. The two high and low level signals of the transient section serve to accelerate and decelerate the mirror state of the transient section from the initial value and set it to the final value, that is, the initial value of the effective section. In this way, acceleration and deceleration in the transient section are effectively performed, and the transient section can be made shorter than in the prior art.

FIG. 2 is a block diagram of an apparatus showing an embodiment of the present invention, which includes a signal generation circuit 1, a drive circuit 2, and a galvanic mirror 3.

As mentioned above, as the speed increases, the inductance of the drive coil cannot be ignored, and the deflection characteristics of the galvanic mirror 3 generally exhibit third-order characteristics (for example, Proceedings of SPIE vol. 84 Laser
Scanning Components and Techniques (1976)
(See pages 62-63). In other words, a large number of orders (in this case, a cubic equation) means a correspondingly large drive delay, which is not suitable for high-speed drive. However, when driven by the drive circuit of the present invention as shown in FIG. 3, for example, the characteristics including the drive circuit can be made quadratic. Therefore, we will now construct this circuit as shown in the diagram, including each resistor, the galvanic mirror drive coil, and
capacitor, each applied signal (R ₀ ~ _{R 5} )
(L, R), (C), (V ₁ ), and set the voltage and current at the positions shown as V ₀ and i _S to analyze this circuit.

First, due to the characteristics of the galvanic mirror, it is electrically expressed as Gdθ/dt+i _S R=V ₀ −Ldis/dt (1) (where G: driving torque coefficient, θ: deflection angle), and the movement of the galvanic mirror is is expressed as Id ² θ/dt ² +P′dθ/dt+K·θ=G·i _S (2) (where I: inertia, P′: control torque coefficient, K: control torque coefficient).

On the other hand, depending on the characteristics of the drive circuit, V ₀ = -V ₁ R ₂ /R ₁ +R ₂ /R ₅・R ₃ /R ₄・R ₀・i _s +R ₂ /R ₅・R ₃・R ₀・Cdis/dt ...(3) It is expressed as. Next, eliminate V ₀ and i _S from equations (1), (2), and (3) to find the relationship between V ₁ and θ.

Here, when adjusting so that L = R ₂ / R ₅ · R ₃ · R ₀ · C (cancels the back electromotive force of the inductance), V ₀ is canceled from equations (3) and (1). Gdθ/dt+i _S R=-V ₁ ¹・R ₂ /R ₁ +R ₂ /R ₅・R ₃ /R ₄・R ₀・i _S (4). Furthermore, by eliminating i _S from equations (4) and (2), Id ² θ/dt ² +P'dθ/dt+K・θ=G ・V ₁ R ₂ /R ₁ −Gdθ/dt/R−R ₀ R ₂ R ₃ / (R ₅ R ₄ ) From this Id ² θ / dt ² + {P′ + G ² / R−R ₀ R ₂ R ₃ / (R ₅ R ₄ )
} dθ/dtKθ=R ₂ /R ₁ G/R−R ₀ R ₂ R ₃ /(R ₅ R ₄ ). As described above, the circuit shown in Fig. 3 detects the current (i _S ) flowing through the drive coil of the galvanic mirror 3, and feeds back the differential signal to the input via the resistor (R ₅ ) to drive the drive coil. It cancels out the back electromotive force caused by inductance (L) and has second-order characteristics. Furthermore, in this circuit, a signal proportional to the current is fed back to electrically make the damping factor variable. In other words, the damping factor ζ is ζ=1/2w ₀・1/I {P′ +G ² /R−R ₀ R ₂ R ₃ /(R ₅ R ₄ )}, (w ₀ ² =K/I) Yes, and in order to increase the damping, R ₀ R ₂ R ₃ /R ₅ R ₄ >0 should be set.

An example in which the present invention is applied to sawtooth deflection with a quadratic characteristic provided by such a drive circuit will be described with reference to FIG. At the time t = t ⁰ (the time corresponding to the final value of the effective section) when the tilting section 10 of the sawtooth movement reaches the maximum, the drive circuit 2 outputs a signal at a level lower than the initial value level of the next effective section, for example, this drive. A signal 11 of the lowest level allowed by the circuit 2 is applied, and the mirror is returned toward the starting point of the inclined portion 10 (the direction corresponding to the initial value of the next effective section) with maximum acceleration. Then, at time t= _t1 , just before the direction of the mirror reaches the starting point, conversely, a signal with a level higher than the final value level of the previous valid section, for example, the highest level signal 12 allowed by the circuit.
is applied, the brake is applied, and the vehicle is further accelerated in the same direction as the inclined portion 10. Then, at a time point t=t ₂ when the speed of the mirror reaches the speed of the sawtooth-like inclined portion 10, the ramp signal is switched to the ramp signal corresponding to the inclined portion 10. However, a signal at a constant level corresponding to the delay of the mirror is superimposed on this ramp signal. For example, if the repetition period of the sawtooth motion is normalized to 1, the resonance frequency of a system with quadratic characteristics is 1.3 times the repetition of the sawtooth wave, and the damping factor is 0.6, then the drive circuit 2 corresponds to the sawtooth motion. When it is possible to drive a signal up to 1.5 times the amplitude of the signal, t ₁ =0.25 and t ₂ =0.31. In this case, the level corresponding to the delay of the mirror of the inclined part is 0.42 for the amplitude ±1 corresponding to sawtooth movement. In this example, a sawtooth motion with a time effective rate of 69% is obtained at a repetition frequency of 77% (0.77=1/1.3) of the resonant frequency.

The present invention can also be applied to single movements. For example, as shown in Figure 5, when you want to synchronize a stationary galvanic mirror with another system to make a single sawtooth motion, you can send a negative level signal and a positive level signal at the right time. By adding this, the mirror can be quickly moved from a resting state to the starting point of sawtooth motion. In FIG. 5, the present invention is also applied to quickly return to a stationary state after completing the slope section and prepare for the next movement.

The present invention can be similarly applied to the case where a continuous sawtooth movement is started in accordance with a certain timing.
In this case, the rising waveform shown in FIG. 5 is added for only the first shot, and from then on, the driving shown in FIG. 4 is performed.

Furthermore, the present invention is not limited to sawtooth movement, but can also be applied to cases in which mirrors are successively set at arbitrary positions, as shown in FIG. 6, for example.

The drive shown in this figure is a case in which a stationary state, a drive (transient), a stationary state, etc. are repeatedly performed.
This kind of mirror movement can be recorded and recorded using light, for example.
It is effective for information recording devices that perform playback or erasing, generally optical disk devices. That is, when the light is on a predetermined track of the disk and the light is rapidly moved (accessed) to a desired track or adjacent to this track. In the case of this example,
Rather than moving the head itself to access the adjacent or desired track, the light itself is track-jumped by driving only the optical deflector (corresponding to a galvanic mirror) installed in the head. , high-speed random access becomes possible. However, even in this case, when the signal level in the stationary state is higher than the signal level in the next stationary state, the levels of the two signals supplied to the transient section are low.
It must be a high level signal.

In either case, the two high and low signal levels added to the transient section may be set to arbitrary values. However, in order to shorten the transient period, it is advantageous to set the levels to the highest and lowest levels allowed by the drive circuit.

According to the present invention, the transition time of mirror movement can be significantly shortened. If we evaluate this at the maximum repetition frequency that provides sawtooth motion with a time effective rate of 70%, we get:
In the conventional technology, as mentioned earlier, the resonant frequency of the mirror is
According to the present invention, the limit was 30-40%.
It is easy to raise it to about 70%, and it is possible to raise it further depending on the value of the damping factor and the two high and low level values set in the transient section. Furthermore, by lowering the allowable range of the time effective rate, it is possible to perform a practical sawtooth motion above the resonant frequency.

On the other hand, when the drive frequency is fixed, the time efficiency can be increased in the present invention.

Furthermore, in the present invention, it is only necessary to set two levels, high and low, in the transient period, and the signal generating circuit 1 may have a simple configuration.

Further, the present invention can take advantage of the feature of the galvanic mirror, which is not limited to repetitive motion, but responds to any signal.

Further, in the present invention, the mirror moves according to the input signal during the effective period, and good deflection characteristics can be obtained. For example, a sawtooth motion with good linearity is possible.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of input signals and mirror movements for galvanic mirror drive according to the prior art, Fig. 2 is a configuration diagram of a device showing an embodiment of the present invention, and Fig. 3 shows a galvanic mirror with secondary deflection characteristics. FIGS. 4 to 6 are explanatory diagrams illustrating an example of a driving circuit for driving a galvanic mirror according to the present invention, and are explanatory diagrams illustrating input signals and mirror movements in various examples of galvanic mirror driving according to the present invention. 1...Signal generation circuit, 2...Drive circuit, 3...
Galva mirror.

Claims (1)

[Claims] 1. The deflection characteristics of an optical deflection device having a mechanically moving mirror are set to secondary characteristics, including a drive circuit for driving this optical deflection device, and The first and second effective sections are driven by a drive signal corresponding to the desired movement of the mirror, and the transition section of the mirror between the first and second effective sections consists of two predetermined levels. The optical deflection device is driven by a signal, and from the final value of the drive signal in the first effective section,
When the initial value of the drive signal in the second valid section is larger, the signal consisting of the two levels is a level signal equal to or higher than the initial value of the second valid section, followed by a signal in the first valid section. If the final value of the drive signal in the first valid section is greater than the initial value of the drive signal in the second valid section, the signal has a level lower than the final value. The optical deflection device is characterized in that the signal consists of a signal at a level lower than the initial value of the second effective interval and a subsequent signal at a level higher than the long final value of the first effective interval. 2. Claim 1, wherein the signal consisting of two predetermined levels consists of the highest level and lowest level signals allowed by the drive circuit.
The optical deflection device described in .