JPH02226223A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To stabilize the automatic excitation of a vibrator by connecting a fixed load resistance element and a variable resistance load element in series with an automatic excitation driving part and lowering the pure resistance value of the impedance of the driving part with the composite resistance of both the elements. CONSTITUTION:One end of the fixed load resistance element B connected to the scanner coil A of impedance Z of the automatic excitation driving part which has an operational amplifier Q1, etc., is grounded. This driving part is provided with the fixed load resistance element r1 and variable load resistance element r2 which are connected in series and the resistance value of the pure resistance of the impedance of the driving part is lowered with the composite resistance of those elements r1 and r2 to stabilize the automatic excitation of the vibrator which vibrates a galvanometer for optical scanning by the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention is applicable to a galvano-mirror (for example, a crystal optical deflector) such as a vibrator that scans light by deflecting it at a predetermined angle, such as a galvano-mirror one-type laser printer. It is concerned with the oscillation circuit used in a scanner (optical scanning device) composed of This relates to an improvement in the oscillation circuit that increases the speed of the oscillation circuit.

<Prior Art> As a technique using a conventional oscillation circuit, there is a known scanner consisting of a laser printer using a galvano-mirror type that scans by deflecting light at a predetermined angle (for example, see Measurement and Control, Vol. .

27, No. 2 (February 1988) P164~
(See page 167).

FIG. 3 is a schematic explanatory diagram of this conventional technique.

FIG. 4 is a diagram for explaining a conventional oscillation circuit.

5 and 6 are diagrams for explaining FIG. 4. FIG.

A conventional scanner A that uses a vibrator to deflect light at a predetermined angle for scanning is configured as shown in FIG. 3, for example.

In FIG. 3, a laser light source 1 modulated by data is shown.
The laser beam from
The beam is deflected by a predetermined angle and scanned. The scanner A has a structure in which the self-excited vibration of the vibrator 2 is controlled by a drive section 3a consisting of a drive coil of an oscillation circuit (driver circuit) 3, etc., and information is written on the photosensitive drum 4.

By the way, in general, the vibrator is rotated to a position θ (-T/K) that is balanced with the torsional constant of a spring (not shown) by generating 1-Luke T due to the torsional force of the oscillation circuit 3. As a result, the incident light from the laser light source 1 is deflected by θ. At this time, the oscillation circuit 3 is configured as shown in FIG. 4, for example, in order to cause the vibrator 2 to undergo stable self-excited vibration, in other words, to control the current of the drive section 3a.

In Fig. 4, when the impedance related to the vibrator and the drive section is 2 (hereinafter this Z will be expressed as a "scanner coil"), this scanner coil 2 is as follows: Z=X+,)Y...(
1). Here, from the impedance characteristic when the vertical axis is the reactance (Ω, I) and the horizontal axis is the frequency as shown in the fifth factor, X is the pure resistance RDC of the scanner coil Z and the resonance point ( resonance frequency f
. ) The resonance resistance component of the drive coil 3a RT e
Combined resistance with S, X = Ro c +Rr e s
-(2) and Y is the impedance of the drive coil 3a.

This scanner coil 2 is incorporated as a piece of a bridge circuit to cause the vibrator to self-excite vibration. At this time, the bridge circuit has an operational amplifier Q1, and the output terminal of this operational amplifier Q1 is connected to a resistor r1 (the resistance value is R+[
One end of resistor r3 (resistance value R3[Ω]) is commonly connected, and the other end of resistor r3 and the other end of the scanner coil Z are commonly connected to the non-inverting terminal of operational amplifier Q1. One output end of the resistor r1 and the other end of the variable resistor r2 are commonly connected and connected to the inverting terminal of the operational amplifier Q1, and one end of the scanner coil Z and one end of the variable resistor r2 are commonly connected and connected to GRD. ing.

Now, the positive feedback amount f+ and the negative feedback amount f- are expressed as f+=Z/ (r30z) −・−(3
)/ =r2/ (r20r+) −(
4), the resonator with the impedance characteristics shown in Fig. 5 will oscillate when f+>, f- by applying two feedbacks as shown in Fig. 4. Become.

By the way, FIG. 6 shows the feedback amount characteristics when the vertical axis represents the feedback amount and the horizontal axis represents the frequency.

From this Figure 6, the amount of negative feedback, ! - for α+(7-), no oscillation occurs because I+<f- in any frequency range,
Also, the amount of negative feedback! - even when α3(7-), oscillation does not occur because f+>f- in any frequency range. On the other hand, in order for stable oscillation to occur at the resonant frequency fθ, the amount of positive feedback is required!
The relationship between + and the amount of negative feedback f- is α2 e of the amount of negative feedback f-
t-), i.e. in the basin centered on the resonance point! ＋〉! -, and in other regions, f+ must be f-, and conversely, oscillation occurs at the resonance point only when such a state is established, so adjust the variable resistor r2 to By setting the circuit in this state, it is possible to operate the vibrator's self-oscillation.

<Problems to be Solved by the Invention> By the way, in this conventional oscillation circuit, normally, for a given resonator, the ! of FIG. The resistance r2 is adjusted so that it becomes 10-α2(, f-).

By the way, now from r2=R2, r2=R2+ΔR2(Ω
) to satisfy the relationship f + = α2 (7>), in order to adjust the tolerance so that oscillation will rise stably even if there is a mistake in the adjustment of r2, f − (
+)≦α2(/−)≦/−(2). Here, f − (1) − Ro c / (
Rres 10r3).

/-(2)-(Roc+RTes)/(R
o c ten RT e s ten r3) ”is).

Then, when r2=R2, α2 (7-)−/−(1
), α2 (f-) f-(2
), so from equation (5), R2/ (RI + R2
) = Roc/ (Roc + rz).

((R2+ΔR2) / (R+ + R2+ΔR2)
)((RDC+RTGs) / (Roc+Rres+r3) l −(
6) is obtained. From this equation (6), Rres/Roc=ΔR2/R2-(7) can be obtained. Here, if RreS is 1Ω and RDC is 100Ω, then from equation (7), ΔR2−(Rres
/Rc+c)・R2(1/100)・R2...(
8). In this way, in a vibrator with Ro c >Rre s, ΔR2 becomes extremely small. That is, α
2 (7) Since the adjustment range is narrow, it is difficult to set <<, and because this adjustment range is very narrow, if the pure resistance value changes due to temperature etc., the set condition will easily be destroyed. , it is difficult to obtain stable oscillation.

The present invention has been made in view of the above problems of the conventional technology, and its purpose is to provide an oscillation circuit that can stably oscillate a vibrator with a simple circuit configuration. It is.

Means for Solving the Problems> In order to achieve the above object, the present invention provides an oscillation circuit that controls self-excited vibration of a vibrator that scans light by deflecting a predetermined angle. A fixed negative resistance element or a variable negative resistance element is connected in series to the drive unit to combine the pure resistance of the impedance related to the vibrator and the drive unit and the fixed negative resistance element or the variable negative resistance element. The present invention is characterized in that the resistance value of the pure resistor is equivalently lowered by a resistor, thereby stabilizing the self-excited vibration of the vibrator.

<Example> Examples will be described with reference to the drawings.

In the following drawings, parts that overlap with those in FIG. 4 are given the same numbers and their explanations will be omitted.

FIG. 1 is a block diagram showing a specific embodiment of the oscillation circuit of the present invention. Here, FIG. 1(A) is a schematic block diagram of an oscillation circuit, and FIG. 1(B) is a circuit diagram showing a specific example of the oscillation circuit of FIG. 1(A).

In FIG. 1(A), B is a negative resistance element (-R) connected in series with the scanner coil Z, which is the drive unit 3a that causes the vibrator to self-excite vibration. This shows the case where the resistance element is a fixed negative resistance element. This fixed negative resistance element B is connected in series with the scanner coil 2 and connected to the other end or GND, and equivalently reduces the value of the pure resistance RDC of the scanner coil 2 by the combined resistance with the pure resistance (in this case This is provided to stabilize the oscillation startup by setting it to zero).

The fixed negative resistor B shown in FIG. 1(A) can be expressed as a more specific circuit configuration example as shown in FIG. 1(B).

In FIG. 1(B), the fixed negative resistor B can be constituted by, for example, a negative impedance converter (hereinafter abbreviated as rNIc) Q2. The configuration of the fixed eroding resistor B is such that the scanner coil Z is connected to the inverting terminal of NICQ2, and the resistor r4 is connected between the inverting terminal and the output terminal of NICQ2.
A resistor r5 is connected between the non-inverting terminal and the output terminal of NICQ2, and one end of a resistor r6 whose other end is connected to GND is connected to the non-inverting terminal of NICQ2. At this time, the resistance value of resistor r6 needs to be changed according to the pure resistance RDC of the vibrator, so generally a variable resistor is used as shown in the figure, but it is recommended to use it as a fixed resistor and replace it each time. Good too. At this time, the resistance value of fixed negative resistance B is R”= , (ra ・re / r5)
...(9).

By configuring the negative resistance B in this way, the composite impedance (Z+
(-R)l is (Z+(-R)) =Roc 1Rres 14Y -+ (r, ・rs)/r5) = (Roc (ra ・re)/r5)+RT
e s +4Y-=OΦ. From this formula, for example, the value of °'-R' is "9".
0Ω", Roc = 100Ω (the value that first escaped) becomes 10Ω, which means that the pure resistance RDC can be equivalently lowered. This means that RD
Even if a scanner with C:>Rr e S is used, the pure resistance RD
C can be made substantially smaller.

As a result, from equation (7), ΔR2 - (1/10) R2...(II), so the allowable amount ΔR2 for adjusting the resistance r2 becomes large, and even if the resistance value R2 slightly fluctuates, α2 (/-) is extremely unlikely to deviate from the stable point, so an oscillation circuit that can stably oscillate at the resonant frequency is constructed.

Note that the negative resistance B is not limited to the circuit described above as long as it can satisfy the function of '-R', and may be configured as shown in FIG. 2, for example.

FIG. 2 is a block system diagram showing another specific embodiment of the oscillation circuit of the present invention, and in particular, FIG.
) is a block diagram of an oscillation circuit corresponding to FIG. In the following drawings, parts that overlap with those in FIG. 1 are given the same numbers, and the explanation thereof will be omitted.

In Figure 2 (A), BO is a negative resistance connected in series with the scanner coil 2 and connected to GND at the other end, corresponding to the negative resistance in Figure 1 (A) (here, the resistance value is Since it consists of a self-exciting variable ms, it will be referred to as a "variable negative resistance" to distinguish it from the case shown in Fig. 1, and its symbol will be changed to "' -
VR”).

Its configuration consists of a scanner coil Z and a variable negative resistance (-VR
) When the RDC changes significantly by supplying DC current I to the two elements (i.e., the change in RDC becomes Ro C>Rr
e s ), it is always equivalently “Ro c−
VR'' is controlled to a constant value (including zero) without being influenced by external conditions such as temperature, that is, the value of the negative resistance can be substantially changed by the control voltage Vc, and under the external conditions. Even if the DC resistance RDC changes, the structure is such that by canceling the change in RDC, the combined resistance value is always fed back to a constant value, making the oscillation startup more stable. For example, the circuit configuration in FIG.
In the figure, it is sufficient to cope with cases where RDC does not change that much, but when ΔRoc>Rres as described above, there is a possibility that the oscillation start-up may become unstable. , only for ΔRDC “
'-vRII is changed.

Incidentally, the capacitor C1 connected to the feedback resistor r3 for direct current is for cutting off the direct current, and is selected so as not to affect the oscillation frequency. A more specific example of circuit failure is shown in FIG. 2(B), for example.

In FIG. 2(B), the configuration of the variable negative resistance B0 is such that a direct current I is connected to the scanner coil Z and the variable negative resistance (-VR).
It has a constant current source IQ that supplies a constant current source IQ, and uses a low-pass filter L that has the function of a voltage controlled resistor VCH in place of the variable resistor r6 in Figure 1 (B).
l) Based on the value obtained by adding and subtracting the voltage component of the DC current I supplied through F and the reference voltage vTef, calculate the FETTT as follows: (Roc - VR) ・T - VT e f=CON
st -(12) (at this time, -VR" is FET
If the resistance of r is R6, -VR--r4- R6/r
6), resulting in Roc V
R=const. Therefore, even if RDC changes due to temperature or the like, "RDC-VR"° can always be kept at a small constant value (or zero). In addition, in such a circuit, when controlling Roc VR=OΩ, the accuracy of the DC current I has no relation to the value of the constant value (Roc VR).

<Effects of the Invention> Since the present invention is configured as described above, it produces the following effects.

(2): A vibrator with Roc>Rres can be stably driven at the resonant frequency.

■: In addition to this, by using the configuration described in the other embodiments, the amount of change due to external factors etc. in RDC can be reduced to Rre.
Stable startup is possible even when the value is sufficiently larger than s.

[Brief explanation of the drawing]

FIG. 1 is a block system diagram showing a specific embodiment of the oscillation circuit of the present invention, FIG. 2 is a block system diagram showing another specific embodiment of the oscillation circuit of the present invention, and FIG. 3 is a block system diagram showing a specific embodiment of the oscillation circuit of the present invention. A schematic explanatory diagram, FIG. 4 is a diagram for explaining the conventional oscillation circuit,
5 and 6 are diagrams for explaining FIG. 4. FIG. 2... Vibrator (galvano mirror), 3... Oscillation circuit, B, Bo... Negative resistance, Z... Scanner coil. ■ Extortion

Claims (1)

[Claims] In an oscillation circuit that controls the self-excited vibration of a vibrator that scans light by deflecting it at a predetermined angle, a fixed negative resistance element or a variable negative resistance element is connected in series to a drive unit that causes the vibrator to self-vibrate. , the resistance value of the pure resistance is equivalently lowered by the pure resistance of the impedance related to the vibrator and the drive unit, and the combined resistance of the fixed negative resistance element or the variable negative resistance element, and the self-excitation of the vibrator is achieved. An oscillation circuit characterized by stabilizing vibration.