JPH0445092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improving the electrical characteristics of an encoder used in a control system for a direct drive motor (hereinafter referred to as DD motor).

[Conventional technology] In systems that detect the rotation of the DD motor using an optical rotary encoder and control the drive of the DD motor based on the detection signal, malfunction of the encoder due to noise etc. can lead to motor runaway and accidents. . Therefore, it is necessary to take measures to prevent noise from entering the encoder.

However, there are noise sources such as 300V and 20V power lines around the encoder. Furthermore, there is a possibility that external noise may be picked up while the encoder detection signal is transmitted to the controller via the signal line.

Therefore, in conventional encoders, the operating voltage of the circuit section is increased to ±15V, for example, to increase the amplitude of the output signal and ensure a sufficient S/N ratio even against external noise. The thing I made was hot.

[Problems to be solved by the invention] However, since this encoder requires a high power supply voltage, it is difficult to integrate the entire circuit into an IC, and there are other problems such as the need to supply both positive and negative power to the encoder. It was hot.

The present invention was made to solve these problems, and aims to realize an encoder that has high noise resistance even at a low power supply voltage and whose circuit can be easily integrated into an IC.

[Means for Solving the Problems] The present invention comprises: a movable code plate in which a slit row in which slits are arranged at a constant pitch is formed; a light-emitting means for shining light onto the slit; Detects the light from the light emitting means that has passed through the slit,
a light receiving means that outputs a current signal according to the amount of detected light; a current/voltage conversion circuit that is provided for each light receiving means and uses an operational amplifier to convert the current signal output by the light receiving means into a voltage signal; and each current/voltage. A switch provided at the output end of the conversion circuit and a switch of a plurality of consecutively arranged light receiving means are closed in accordance with the arrangement order of the light receiving means,
a scanning means for scanning the detection signal of the light receiving means; an addition circuit for calculating the sum of the scanned detection signals using an operational amplifier and outputting a signal corresponding to the displacement of the code plate; the current/voltage conversion circuit and the addition circuit. The encoder includes a reference voltage applying means for applying different reference voltages to the operational amplifiers of the encoder.

[Example] Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a block diagram of an embodiment of an encoder according to the present invention.

In the figure, 1 is a code plate which has a slit row in which slits 2 are arranged at a constant pitch and is rotatable in the b-b' direction, 3 is a light emitting means such as an LED, and 4 is a parallel light source for the light from the light emitting means 3. The lens 5 is a light receiving means for detecting the light passing through the slit 2. The light receiving means 5 is one of the slits 2.
Multiple pieces are arranged in a pitch. As such a light receiving means, for example, a photodiode array (hereinafter referred to as PDA) is used. The photodiode array 5 shown in the figure is an array of eight photodiodes 5 ₁ to 5 ₈ . The photodiodes 5 ₁ to 5 ₈ output current signals according to the detected amount of light.

6 scans the detection signals of photodiodes 5 ₁ to 5 ₈ to generate a rotation angle signal θ _sig corresponding to the displacement of the code plate 1.
This is a signal processing circuit that outputs .

A specific configuration of the signal processing circuit 6 is shown in FIG.

In the figure, 61 ₁ to 61 ₈ are current/voltage conversion circuits. This circuit uses operational amplifiers A ₁ -A ₈ in which a resistor R is connected between the inverting input terminal and the output terminal, and converts the output current signals of the photodiodes 5 ₁ -5 ₈ into voltage signals. The divided voltage _Vs1 of the drive voltage _Vcc is used as the reference voltage for the operational amplifiers _A1 to _A8 .

62 ₁ to 62 ₈ are analog switches connected to the output terminals of operational amplifiers A ₁ to _{A 8} .

Reference numeral 63 denotes a shift register that provides open/close signals to the switches 62 ₁ to 62 ₈ and sequentially shifts these open/close signals. The shift register 63 performs shifting at the timing given by the clock signal CLK.

Reference numeral 64 denotes an adding circuit that adds voltage signals taken out by closing the switches 62 ₁ to 62 ₈ to generate a rotation angle signal θ _sig . This circuit uses a summing amplifier U in which a resistor R ₁ is connected to an inverting input terminal and a resistor R ₂ is connected between an output terminal and an inverting input terminal. Reference voltage of summing amplifier U
V _s2 is the drive voltage V _cc divided by a resistor, and is different from the reference voltage V _s2 . Further, the other end of the resistor R ₁ is connected to the switch 62 .

Here, the scanning means referred to in the claims is the shift register 63, and the reference voltage applying means are resistors _R3 to _R5 connected in series, with one end connected to the drive voltage _Vcc and the other end connected to the common. .

Next, the operation of such an encoder will be explained.

The output current of each photodiode 5 ₁ to 5 ₈ changes from 0 to i depending on the amount of detected light. The shift register 63 has 4 of the 8 switches 62 ₁ to 62 ₈
Turn on all the switches at the same time, and shift the switch to turn on according to the CLK signal.

Here, like the conventional signal processing circuit, the amplifier A
(Amplifiers A ₁ to A ₈ ) and U with the same reference voltage (hereinafter referred to as a single reference voltage) corresponds to the circuit shown in Figure 2 where V _s1 = V _s2 . The maximum and minimum values of the rotation angle signal θ _sig are as follows.

θ _sig (max) = V _s1 + (iR/R ₁ ) x 4 x R ₂ = V _s1 + 4iR x (R ₂ / R ₁ ) (1) θ _sig (min) = V _s1 (2) R, R ₁ , _R2 : Resistance values of resistors R, _R1 , and _R2 , and the output voltage of the signal processing circuit 6 is limited to V _s1 ~ (maximum output voltage of amplifier U), making it impossible to obtain sufficient dynamic range. .

On the other hand, as in the circuit shown in Figure 2, the reference voltage V _s1 and
When V _s2 is made different, the maximum and minimum values of the rotation angle signal θ _sig are as follows.

θ _sig (max) = V _s2 + 4 x (V _s2 - V _s1 + iR) x (R ₂ / R ₁ ) (3) θ _sig (min) = V _s2 + 4 x (V _s2 - V _s1 ) x (R ₂ /R ₁ ) (4) By appropriately selecting the values of R ₁ , R ₂ , V _s1 , and V _s2 in equations (3) and (4), the output voltage of the signal processing circuit 6 can be adjusted within the output voltage range of the amplifier U. Can be expanded to full size. An enlarged example is shown in FIG.

In FIG. 3, a ₁ and a ₂ are the output voltage ranges of amplifiers A and U.

Figure a shows the output voltage range when V _s1 = 8V and V _s2 = 5V, and Figure b shows the output voltage range when V _s1 = 5V and V _s2 = 4V.

By choosing an appropriate reference voltage value as shown in figure b, a dynamic range of 6V can be obtained with a reference voltage of 5V or less.

FIG. 4 is a diagram showing the main part of another embodiment of the encoder according to the present invention.

In this embodiment, the reference voltages of amplifiers A and U are level-shifted without providing two reference voltages.

In the figure, a current from a current source I flows into an inverting input terminal of an amplifier U, and a non-inverting input terminal is connected to a reference voltage V _s1 . In this circuit, the rotation angle signal can be lowered to θ _sig (min) = V _s1 −IR ₂ I: the current of the current source I, and by appropriately selecting the values of R ₁ and R ₂ , the signal processing circuit 6 The dynamic range of the amplifier can be extended to the full output voltage range of the amplifier U.

Note that the number of photodiodes provided within one pitch of the slit 2 may be other than eight.

Further, the number of switches that can be closed simultaneously may be other than four.

Furthermore, the code plate 1 is not limited to one that is rotatably displaced, but may be one that is linearly displaced.

[Effects] According to the present invention, since the signal processing circuit 6 is internally equipped with means for level shifting the reference voltages of the amplifiers A and U, a rotation angle signal θ _sig of large amplitude can be obtained with a low power supply voltage. Therefore, even when compared with a conventional single reference voltage circuit, an output signal with a high S/N ratio can be extracted even with the same power supply voltage. Furthermore, according to the present invention, a low power supply voltage is required to obtain signals of the same amplitude, making it easy to unify the drive voltage V _cc and to integrate the signal processing circuit into an IC. When the signal processing circuit according to the present invention is made into a monolithic IC, for example, the same amplitude as the output signal obtained by a conventional single reference voltage circuit with a power supply voltage of ±15V can be obtained.
Can be obtained with a power supply voltage of 10V.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the encoder according to the present invention, FIG. 2 is a configuration diagram of the main parts of FIG. 1, FIG. 3 is an explanatory diagram of the operation of the encoder in FIG. FIG. 2 is a configuration diagram of main parts of another embodiment of the encoder according to the present invention. DESCRIPTION OF SYMBOLS 1... Code plate, 2... Slit, 3... Light emitting means, 5... Light receiving means, 6... Signal processing circuit, 61
₁ ~ 61 ₈ ... Current/voltage conversion circuit, 62, 62 ₁
~62 ₈ ...Switch, 63...Shift register,
64...Addition circuit, R, _R1 to _R5 ...Resistance, A,
_A1 to _A8 , U... operational amplifier.

Claims (1)

[Scope of Claims] 1. A movable code plate having a slit row formed with slits arranged at a constant pitch, a light emitting means for emitting light to the slits, and a plurality of slits arranged within one pitch of the slits. , detecting the light from the light emitting means that passed through the slit,
a light receiving means that outputs a current signal according to the amount of detected light; a current/voltage conversion circuit that is provided for each light receiving means and uses an operational amplifier to convert the current signal output by the light receiving means into a voltage signal; and each current/voltage. A switch provided at the output end of the conversion circuit and a switch of a plurality of consecutively arranged light receiving means are closed in accordance with the arrangement order of the light receiving means,
a scanning means for scanning the detection signal of the light receiving means; an addition circuit for calculating the sum of the scanned detection signals using an operational amplifier and outputting a signal corresponding to the displacement of the code plate; the current/voltage conversion circuit and the addition circuit. An encoder comprising a reference voltage applying means for applying different reference voltages to an operational amplifier.