JPH0115804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a phase detection type scale device suitable for use in devices that measure the amount of relative movement between two relatively moving objects.

Prior to describing the present invention, a general phase detection type scale device will be described with reference to FIG.

The phase detection type scale device shown in Fig. 1 is one in which magnetic powder is coated on a glass plate or metal band.
A magnetic scale 1 is obtained by magnetically recording a sine wave or the like at a characteristic wavelength λ on a rod-shaped high permeability material to form a magnetic grating pattern, and a pair of saturable type magnetic scales are formed using the magnetic grating of this magnetic scale 1 as a reference scale. The magnetic heads 2a and 2b read the information and convert it into an electrical signal. These pair of saturable magnetic heads 2a,
2b are arranged with an interval of (m+1/4)λ (m is an integer) from each other, that is, with an electrical phase difference of 90°. Here, the magnetic head 2a,
2b uses a so-called multi-gap head, each having a plurality of gaps at intervals corresponding to the characteristic wavelength λ of the magnetic grating, thereby enhancing the wavelength selection effect and improving the reproduction characteristics.

Such a pair of magnetic heads 2a, 2b includes:
Detection windings 3a, 3b and excitation winding 4, respectively.
a, 4b are provided, and excitation windings 4a and 4
Excitation currents i ₁ and i ₂ having phases different from each other by 45° (=π/4) are passed through b.

i ₁ = Isin (1/2ω ₀ t + π/4)… i ₂ = Isin (1/2ω ₀ t)… Also, the pair of magnetic heads 2a and 2b are arranged with an interval of (m+1/4)λ from each other. The magnetic fields h ₁ and h ₂ received by the magnetic heads 2a and 2b are out of phase with each other by 90° (=π/2). That is, when x is the distance from the position where the magnetic field on the magnetic scale 1 is zero, h ₁ =Hsin2π/λx... _h2 = Hcos2π/λx... Therefore, the output signals e ₁ and e ₂ from the detection windings 3a and 3b of each magnetic head 2a and 2b are as follows: e ₁ =E ₁ sin2π/λx・cosω ₀ t … e ₂ =E ₂ cos2π/λx・sinω ₀ t …. I, H, E ₁ and E ₂ in these formulas are constants determined by circuit constants, magnetic field strength of the magnetic scale 1, etc., respectively.

Next, the output signals e ₁ and e ₂ from these detection windings 3a and 3b are sent to a summing amplifier 6 via preamplifiers (head amplifiers) 5a and 5b, respectively.
The output signal e _P from the summing amplifier 6 is e _P =Esin(ω ₀ t+2π/λx) . . . The output signal e _P shown in this equation is a phase modulation signal whose amplitude E is constant and whose phase changes in proportion to the position x on the magnetic scale 1. Note that the preamplifiers 5a and 5b are connected to each magnetic head 2a,
This is for making the output levels from the detection windings 3a and 3b of 2b equal to each other and sending them to the summing amplifier 6.

By the way, in the above equation, only the necessary signal components are described to simplify the explanation, but in reality, the excitation signal components of the magnetic head and their harmonic components, and signals with twice the carrier frequency are used. component and its harmonic components. For example, the signal e _PA including harmonics obtained from the summing amplifier 6 is as follows: e _PA =A ₁ sin1/2ω ₀ t+A ₃ sin3/2ω ₀ t+…+A
_2o-1 sin2n−1/2ω ₀ t+… +B ₂ sin(ω ₀ t+2π/λx)B ₄ sin(2ω ₀ t+2
π/λx)+...+B _2o sin(nω ₀ t+2π/λt)+...
It is expressed as The frequency spectrum of the output signal e _PA of this equation is as shown in FIG. 2, and the frequency f ₀ in FIG. 2 is ω ₀ /2π. Therefore, the amplitudes of frequencies 1/2f ₀ , f ₀ , 3/2f ₀ , 2f ₀ , ... are the above A ₁ , respectively.
B ₂ , A ₃ , B ₄ , ... and these signal components are respectively a ₁ , b ₂ , a ₃ , b ₄ , ..., then the signal component b ₂ of frequency f ₀ is the position detection signal of the above equation. becomes the phase modulation signal e _P for. In order to extract only this signal component b ₂ , a band pass filter 7 is used which sets the frequency f ₀ as the center of the pass band and blocks the signal components a ₁ and a ₃ at frequencies 1/2f ₀ and ₃ /2f 0. It is necessary to use it.

FIG. 3 shows an example of the frequency characteristics of the bandpass filter 7, with the vertical axis representing the response or voltage gain. The center frequency of the passband P in FIG. 3 is f ₀ , and it is necessary to sufficiently reduce the output level at frequencies 1/2f ₀ and 3/2f ₀ within the stopbands E ₁ and E ₂ . The width of the passband P determines the response speed of the scale device. This is because the position x changes with time when the magnetic heads 2a, 2b and the magnetic scale 1 are moved relatively, so the frequency of the signal e _P in the above equation, that is, the signal component b ₂ in FIG. fluctuates around f ₀ . For example, when the above relative movement speed is ±v, the initial value
Since x ₀ = 0 and x = ±vt, the angular frequency is ω =
It varies as ω ₀ ±2π/λv. Therefore, the greater the relative moving speed v, the higher the signal component b ₂ will be at the frequency f ₀
The wider the passband P of the bandpass filter 7, the more the bandpass filter 7 can respond to a large relative movement speed, that is, the position detection and movement amount detection can be performed normally.

Next, the output from the bandpass filter 7 is amplitude limited by a limiter amplifier 8, converted into a rectangular wave signal by a waveform shaping circuit 9, and then passed to an interpolation circuit 1.
Sent to 5. The interpolation circuit 15 is supplied with a signal with a frequency nf ₀ from a reference oscillator 10, which will be described later, and electrically reads a more accurate scale obtained by equally dividing the characteristic wavelength λ of the magnetic scale 1. Movement amount detection signals are output from the first and second output terminals 16a and 16b, respectively, depending on the positive and negative directions of the relative movement.

Next, the reference oscillator 10 generates n of the reference frequency f ₀
It oscillates at twice the frequency nf ₀ , and this oscillation output is sent to the interpolation circuit 15. Also, this frequency
The oscillation output of nf ₀ is frequency-reduced to 1/2n via the frequency reduction circuit 11, and the 1/2f ₀ component is extracted by the low-pass filter 12. This frequency 1/2
The f ₀ component is phase-shifted by π/4 in the phase shifter 13, and is then passed through the excitation amplifier 14a to the excitation coil 4a of the magnetic head 2a, and via only the excitation amplifier 14b to the excitation coil 4b of the magnetic head 2b. are sent to each.

According to such a conventional example, from the output signal e _PA from the summing amplifier 6 (see formula and FIG. 2),
A bandpass filter 7 is used to extract only the signal component _b2 necessary for detecting the amount of movement and position. As shown in FIG. 3, this bandpass filter 7 requires a filter circuit configuration in order to obtain response changes at the rise and fall of the frequency characteristic curve. It becomes expensive. Furthermore, if you try to make the rise and fall of the frequency characteristic curve steeper in order to increase the response speed of the scale device, you will have to increase the number of filter stages or use high reactance elements, and you will also have to increase the number of filter stages and use high reactance elements. The configuration becomes complicated and the price becomes high.

Next, FIG. 4 shows another conventional example, which is used in a scale device with a relatively coarse resolution (for example, about 5 μm or 10 μm). The reference oscillator 30 in this example has a frequency nf ₀ and a duty of 50, for example.
% rectangular wave pulse, and this pulse output is passed through a frequency reduction circuit 3 using a counter etc.
1 to 1/m, and the frequency reduction circuit 32 reduces the frequency to m/2n. The output of this frequency reduction circuit 32 is passed through an excitation amplifier 34b to the detection winding 4b of the magnetic head 2b similar to the above, and after being phase-shifted by π/4 by a phase shifter 33, it is sent to the excitation amplifier 34a. The signals are sent to the excitation windings 4a of the magnetic head 2a through the respective excitation windings 4a.

Further, an attenuator 25 for gain adjustment is inserted and connected to either one of the outputs from the detection windings 3a, 3b of the pair of magnetic heads 2a, 2b, and the output voltage from both magnetic heads 2a, 2b is are made equal and applied to the summing amplifier 26. The center frequency of the passband of the bandpass filter 27 is selected to be (n/m-1)f ₀ or (n/m+1)f ₀ . The output from the bandpass filter 27 is sent to a phase comparison circuit 37 via a limiter amplifier 28 and a waveform shaping circuit 29. This phase comparison circuit 37
is constructed using, for example, a D-type flip-flop, and the reference oscillator 3 is used as the clock signal.
The oscillation output from 0 is used as an m-phase clock in the clock output circuit 38. The output from this phase comparison circuit 37 is sent to an interpolation circuit 35. This interpolation circuit 35 is also supplied with an m-phase clock from a clock output circuit 38.

The conventional example shown in FIG. 4 also has a bandpass filter 27 similar to the conventional example shown in FIGS.
This makes the circuit configuration complicated and expensive, and it is difficult to increase the response speed.

The present invention has been made in order to eliminate such conventional drawbacks, and provides a phase detection type scale device that can extract only the above-mentioned phase modulation signal for detecting the above-mentioned relative movement amount with a simple configuration. The purpose is to provide the following.

Hereinafter, preferred embodiments of the present invention will be described.
This will be explained with reference to FIGS. 5 to 7.

First, in the phase detection type magnetic scale device shown in FIG. ) Two saturable magnetic heads 2a and 2b, which are scale detection elements, are arranged at an interval of . These saturable magnetic heads 2a, 2b include a detection winding 3.
a, 3b, and excitation windings 4a, 4b, respectively, and the excitation windings 4a, 4b are connected to each other.
Excitation currents i ₁ and i ₂ (see the formula above) with a frequency of 1/2f ₀ having a phase difference of 45° (=π/4) are flowing.
In addition, output signals e ₁ and e ₂ from the detection windings 3a and 3b
As is clear from the above equation, the amplitudes of the carrier signals of frequency f ₀ (=ω ₀ /2π) are at a position of 90° from each other depending on the position x of the head on the magnetic scale 1. The signal changes with a phase difference. The output signals from these magnetic heads 2a, 2b are sent to a summing amplifier 6 via preamplifiers 5a, 5b, respectively. The phase modulation signal from the summing amplifier 6 is the signal e _P expressed by the above-mentioned equation, but in reality, a signal e _PA including harmonics as shown in the equation is obtained. The frequency spectrum of this signal _ePA is expressed as shown in FIG. 2 mentioned above. In Fig. 2, the phase modulation signal e _P of the above formula has a spectrum b ₂ near the frequency f ₀ , and in the past, only this phase modulation signal component was extracted using a bandpass filter 7 (or 27, etc.). That's why.

The present invention provides an addition output signal e _PA including this harmonic.
The excitation signal components and their harmonic components, that is, the signal components a 1 , a 3 , a ₄ , ... whose frequencies are ₁ /2f ₀ , ₃ /2f ₀ , 5/2f ₀ , ... are filtered through a comb-tooth filter 17 . Among _the signal components _b2 , _b4 , _b6 , .

The comb filter 17 is composed of a delay circuit 18 and an adder 19, and the adder 19 adds the signal e _PA and a signal obtained by delaying the signal e _PA by a time Δt by the delay circuit 18. By doing so, the comb tooth characteristic is obtained. By setting the delay time Δt of the delay circuit 18 so that a delay of 1/2 cycle occurs for the signal with frequency 1/2f ₀ , only the frequency 1/2f ₀ and its harmonic components can be removed. Can be done.

To explain this in detail with reference to mathematical formulas, first, of the signal e _PA in the above formula, when the excitation signal component is f(t) and the phase modulation signal component is g(t), f(t)= A ₁ sin1/2ω ₀ t+A ₃ sin3/2ω ₀ t+
…+A _2o-1 sin2n−1/2ω ₀ t+… = _∞ 〓 ⁿ⁼¹ A _2o-1 sin2n−1/2ω ₀ t … g(t)=B ₂ sin(ω ₀ t+2π/λx)+B ₄ sin( 2
ω ₀ t+2π/λx)+…+B _2o sin(nω ₀ t+2π/λx)
+… = _∞ 〓 ⁿ⁼¹ B _2o sin(nω ₀ t+2π/λx)… It can be expressed as follows. Next, this signal e _PA (=f(t)+g
(t)) is delayed by the above-mentioned time Δt (=2π/ω ₀ ) by the delay circuit 18 of the comb-tooth filter 17, so the delayed signal f(t+△
t) is f(t+△t)=f(t+2π/ω ₀ )=A ₁ sin2
/1ω ₀ (t+2π/ω ₀ )+A ₃ sin3/2ω ₀ (t+2π/
ω ₀ )＋… =−A ₁ sin1/2ω ₀ t−A ₃ sin3/2ω ₀ t…=−
_∞ 〓 ⁿ⁼¹ A _2o-1 sin2n-1/2ω ₀ t=-f(t)... Therefore, the excitation signal component at the output of the adder 19 becomes f(t)+f(t+Δt)=0... and is removed.

Therefore, the output signal from the comb filter 17 is only the phase modulation signal component g(t).
This output signal is sent to a balanced modulator 20 and balanced modulated by an excitation signal of frequency 1/2f ₀ . This means that g(t) is multiplied by sin1/2ω ₀ t, and if we set g(t)・sin1/2ω ₀ t=g _s (t), then g _s (t)=sin1/2ω ₀ t・_∞ 〓 〓 ⁿ⁼¹ B _2o sin(nω ₀ t+2π/λx)=B ₂ /2cos(1/2ω
₀ t+2π/λx)−B ₂ /2cos(3/2ω ₀ t+2π/λx
) +B ₄ /2cos (3/2ω ₀ t+2π/λx) −B ₄ /2cos
(5/2ω ₀ t+2π/λx)+… =B ₂ /2cos (1/2ω ₀ t+2π/λx)+ _∞ 〓 ⁿ⁼¹ B′ _2o cos(2n+1/2ω ₀ t+2π/λx)… However, B′ _2o = 1/2 (B _2o+2 −B _2o ). As is clear from this formula, the frequency f ₀
The signal component with amplitude B ₂ is converted to 1/2ω ₀ (frequency f ₀ /2), and the other frequency components are also shifted to the lower frequency side by f ₀ /2, so the signal component with amplitude B 2 is converted to 1/2ω 0 (frequency f 0 /2). It becomes a frequency spectrum.

The output signal from the balanced modulator 20 is passed through a low-pass filter 21 having frequency characteristics as shown in _FIG .
Only the signal component with the amplitude B ₂ /2 can be extracted.

The frequency characteristics of this low-pass filter 21 are as follows at the frequency 3/2f ₀ of the second harmonic of the phase modulation signal.
It is sufficient that the response is sufficiently reduced, and even if the characteristic curve does not fall steeply, it is easy to widen the width of the passband P. Therefore, despite the simple circuit configuration and the small number of parts, the above-mentioned response speed can be increased, and an inexpensive, high-performance phase detection type scale device can be easily provided. Furthermore, the possibility of using a gyrator or the like as an inductance element for a filter increases, and this can greatly contribute to miniaturization through integrated circuits.

The output signal from this low-pass filter 21 is
The point where the angular frequency is ω ₀ /2 (and the amplitude
B ₂ /2) is the same as the signal of the above-mentioned formula, and is a phase modulation signal in which the amplitude is constant and the phase changes in proportion to the position x on the magnetic scale 1. This phase modulated signal is passed through a limiter amplifier 8 and a waveform shaping circuit 9 to an interpolation circuit 1.
I am sending it to 5. These limiter amplifier 8, waveform shaping circuit 9, and interpolation circuit 15 are similar to each circuit shown in FIG. 1 described above.

The other configuration of this embodiment is the same as that of the conventional example shown in FIG. 1, so the same reference numerals are given to the parts that perform the same operations in the figure, and the explanation will be omitted.

As is clear from the above description, according to the phase detection type scale device according to the present invention, among the signals obtained from the scale detection element, the phase modulation signal (frequency f ₀ ) is Adjacent unnecessary signal components on the frequency side (frequency f ₀ /2 and 3f ₀ /2)
is removed by the comb filter mentioned above,
This eliminates the need for a band-pass filter with a steep slope of the characteristic curve, makes it possible to extract the phase modulation signal using a low-pass filter with a relatively gentle slope, and allows the phase modulation signal to be finally extracted to be transferred to the above-mentioned balanced modulation circuit. By converting to the lowest frequency, f ₀ /2, and increasing the frequency ratio with the adjacent unnecessary signal component (frequency 3f ₀ /2), the frequency characteristics required for a low-pass filter can be further improved. It can be relaxed. In other words, the frequency characteristics of a filter are expressed as a numerical value relative to the frequency ratio, such as the slope of the characteristic curve of 6 dB/oct., and generally speaking, the larger this numerical value, the higher the order of the filter and the more complex its configuration. However, as mentioned above, when the frequency ratio between the necessary signal (frequency f ₀ /2) and the unnecessary signal (frequency 3f ₀ /2) is large, separation is not possible even if the slope of the characteristic curve is made gentler. This can be done effectively and allows for a wide bandwidth.

Therefore, according to the present invention, in a transport detection type scale device, it is possible to replace a conventional band-pass filter, which has a complicated circuit configuration and is expensive, with a low-pass filter, which has a simple configuration and is inexpensive, and has a wide bandwidth. Further, the circuit configuration can be simplified, in particular, the number of inductance elements can be reduced, and it is also possible to form an integrated circuit by employing a wire letterer or the like, thereby making it possible to miniaturize the circuit and reduce costs.

Furthermore, since the passband width of the filter can be widened, the response speed of this scale device can be greatly increased to realize high-speed response.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be easily applied to a scale device using, for example, inductosin.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an example of a conventional phase detection type scale device, FIG. 2 is a graph showing the frequency spectrum of the output signal from the summing amplifier 6 in FIG. 1, and FIG. Pass filter 7
FIG. 4 is a block circuit diagram showing another conventional example. Figures 5 to 7
The figures show an embodiment according to the present invention, in which FIG. 5 is an overall block circuit diagram, FIG. 6 is a graph showing the frequency spectrum of the output signal of the balanced modulator 20, and FIG. 7 is the frequency of the low-pass filter 21. It is a graph showing characteristics. DESCRIPTION OF SYMBOLS 1... Magnetic scale, 2a, 2b... Magnetic head, 6... Addition amplifier, 17... Comb tooth filter, 18... Delay circuit, 19... Adder, 20...
...Balanced modulator, 21...Low pass filter.

Claims (1)

[Claims] 1. A relatively movable scale detection element is arranged opposite to a scale having a scale pattern with a characteristic wavelength λ, and the frequency of the excitation signal of this scale detection element is
In a phase detection type scale device that calculates the relative movement amount based on a phase modulation signal with a frequency f ₀ that is twice f ₀ /2, the frequency f ₀ /2 is determined from the output signal of the scale detection element.
a comb-tooth filter comprising a delay circuit and an adder for removing the excitation signal and its odd-numbered harmonic components at frequencies 3f ₀ /2, 5f ₀ /2, . . . ; The above phase modulation signal of frequency f ₀ obtained from and its harmonic component frequency
A balanced modulation circuit for shifting the signal components of 2f ₀ , 3f ₀ , 4f ₀ , ... to the lower frequency side by f ₀ /2 by the excitation signal of frequency _{f 0} /2; The phase modulation signal converted to /2 is passed and the frequency is 3f ₀ /2,
A phase detection type scale device comprising a low-pass filter for removing harmonic components converted to 5f ₀ /2, .