JPH01282423A - Optical encoder - Google Patents

Abstract

PURPOSE:To enable highly accurate calculation of a position data, by providing a subtraction circuit to subtract an extinguishing signal stored into an extinguishing signal memory section from a lighting signal detected when a light emitting element is lighted. CONSTITUTION:A current ILED applied to an LED 1 is controlled with an emission control section 2 so as to regulate the lighting and extinguishing of the LED 1 at a specified timing. At this point, an output light is converted into electricity with light receiving elements 4a and 4b and detected as light output V1 through an analog amplifier 5. The control section 2 samples an offset component as light output V11 with a sampling/holding circuit 6 when the LED 1 is put out to hold a value thereof. Then, the output V11 is subtracted from the output V1 at an A/D conversion timing in the lighting of the LED 1 to convert a light output V2 with the offset component corrected into digital from analog. Thereafter, by repeating this operation, a position data can be calculated at a high accuracy by a normal light output with the offset component removed.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to an optical encoder that calculates position data of tables and motors of NG machine tools, etc., and particularly relates to an optical encoder that can calculate position data with high accuracy. .

<Prior art> An optical encoder detects the light output emitted from one light emitting element by a light receiving element placed opposite to one light emitting element, and generates position data representing the rotation angle of the motor, etc. according to the light output level. is being calculated.

A fixed slit plate and a rotating slit plate are provided between the light emitting element and the light receiving element, and when the rotating slit plate is rotated, the light incident on the light receiving element changes depending on the degree of overlap between the rotating slit and the fixed slit. The amount of incident light is limited,
It is variable at a constant cycle.

FIG. 5 is a characteristic diagram showing the optical output detected by the light receiving element.

The optical output is detected as a sine wave signal with one period between slits provided adjacently on the rotating plate. The arrow ↑ in the figure indicates the timing at which the optical output is referred to when calculating the position data, and the arrow mark indicates the timing at which the optical output becomes the minimum.

The position data, for example, the rotation angle θ, is determined by referring to the optical output of a cosine wave signal (not shown) whose phase is delayed by 90 degrees from the sine wave signal together with the sine wave signal at the above timing, and based on the optical output of both, the following is performed. It is calculated by calculation formula (101).

COSθ <Problem to be solved by the invention> However, due to temperature changes or aging, current (called dark current) flows through the light receiving element even when the light emitting element, which is not supposed to detect light output, is turned off, causing the apparent In this case, the upper optical output may be detected, or the offset voltage of the amplifier itself, which is installed for the purpose of amplifying the detected weak optical output, may change due to temperature changes or aging, etc., and the light emission may be interrupted. The light-off signal did not become zero even though the element was off.

For this reason, there is a serious problem in that the position data causes errors in response to the lights-out signal, and is calculated as inaccurate position data.

In light of the above, an object of the present invention is to provide an optical encoder that can remove the lights-off signal, which causes errors, from the lights-on signal and can calculate position data with high precision.

Means for Solving the Problems> FIG. 1 is a block diagram of a main part of an optical encoder showing one embodiment of the present invention.

1 is a light emitting diode (LED) serving as a light emitting element; 2 is a light emission control section; 3 is a light output detection section which also serves as a lighting signal detection section and a lighting off signal detection section; 4a and 4b are light receiving elements; 5 is an analog amplifier; 6 is an analog amplifier. A sample and hold circuit serves as a light-off signal storage section, 7 is a subtraction circuit, and 8 is an A/D converter.

Function> The light emission control unit 2 controls the lighting and extinguishing of the light emitting diode 1 at predetermined timing, and the light output detection unit 3 detects a signal when the light emitting diode 1 is turned off. The light-off signal thus obtained is stored in the sample & hold circuit 6, and the subtraction circuit 7 subtracts the light-off signal stored in the sample & hold circuit 6 from the light-on signal detected when the light emitting diode 1 is turned on.

<Embodiment> FIG. 1 is a block diagram of essential parts of an optical encoder showing an embodiment of the present invention. Note that the subtraction in this embodiment is performed using a lighting signal and a lighting-off signal that are analog data.

In the figure, 1 is a light emitting diode (LE) which is a light emitting element.
D), 2 is a light emission control section, which controls the lighting and extinguishing of the light emitting diode 1 at a predetermined timing. For example, lighting is performed at the timing indicated by the arrow ↑ shown in FIG. 5, and extinguishing is performed at the timing indicated by the arrow ↑ between the arrows ↑. Further, the first light emission control unit 2 causes a sample and hold circuit 6 (described later) to store a light-off signal when the light is turned off, and causes a subtraction circuit 7 (described later) to subtract the stored light-off signal from the light-on signal when the light is turned on.

3 is a light output detection section that serves as a lighting signal detection section and a lights-off signal detection section, which detects the light output V□ (lighting signal) when light emitting diode 1 is turned on and the light output when 5 light emitting diode 1 is turned off. V□1 (light-off signal) is detected. 4a, 4b
is a light receiving element, the light receiving element 4a detects the above-mentioned sine wave signal, and the light receiving element 4b detects a cosine wave signal. Reference numeral 5 denotes an analog amplifier, which amplifies the weak optical output detected by the light receiving elements 4a and 4b to a level required for subsequent processing.

6 is a sample and hold circuit which serves as a light-off signal storage section, and when the light emitting diode 1 is turned off, the light output detection section 3
The optical output voltage V detected at is stored.

A subtraction circuit 7 subtracts the optical output v1□ stored in the sample and hold circuit 6 from the optical output v1 detected when the light emitting diode 1 is turned on, and corrects the optical output v2 to a normal value. 8 is an A/D converter, which converts the corrected analog optical output v2 into digital data.

Next, the operation of the embodiment shown in FIG. 1 will be explained with reference to the timing chart shown in FIG.

LED current ILEII applied to light emitting diode 1
is controlled by the light emission control section 2 to control the lighting and extinguishing of the light emitting diode 1 at predetermined timing. The light output at this time is photoelectrically converted by the light receiving element 4a and detected as the light output V□ via the analog amplifier 5 (the light receiving element 4b will be omitted). The optical output VU has an offset amount, which is an error component, due to the dark current of the light receiving element 4a, the offset voltage of the analog amplifier 5, and the like.

The light emission control unit 2 controls when the light emitting diode 1 is turned off (arrow 1t
), the sample and hold circuit 6 is used to sample the offset amount which is the optical output V□□.

Hold that value.

Next, at the A/D conversion timing when the light emitting diode 1 is turned on (arrow ↑), subtract the light output V when the light is turned off from the light output V when the light is turned on, and obtain the optical output v2 with the offset corrected. A/D conversion.

Thereafter, the above operations are repeated to calculate position data with high accuracy using the normal optical output with the offset removed.

FIG. 3 is a block diagram of essential parts of an optical encoder showing another embodiment of the present invention. Note that the subtraction in this embodiment is performed using a lighting signal and a lighting-off signal that are digital data.

In the figure, the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and 11 is an A/D converter.

The optical output of analog data output from the photodetector 3 is converted into digital data. Reference numeral 12 denotes a lighting signal latch, which holds digital data of the optical output V when the light emitting diode 1 is lit. Reference numeral 13 denotes a light-off signal latch, which stores digital data of the optical output V□1 when one light emitting diode is turned off. 14 is a digital subtraction circuit, which subtracts the optical output V□1 stored in the light-off signal latch 13 from the light output V□1, which is detected when 2 light emitting diodes are turned on and held in the lighting latch 12, and 1 is turned on. Correct the signal to the normal value.

Next, the operation of the embodiment shown in FIG. 3 will be explained with reference to the timing chart of FIG. 4.

LED current TLE applied to the light emitting diode 1. is controlled by a light emission control section 2 so as to control the lighting and extinguishing of one light emitting diode 1 at a predetermined timing. The light output at this time is photoelectrically converted by the light receiving element 4a and outputted from the light output detection section 3 as analog data. This analog data is converted into digital data by the A/D converter 11.

The light emission control unit 2 uses the light-off signal latch 13 at the A/D conversion timing (arrow?) when one light-emitting diode 1 is turned off, and latches the light output V s x corresponding to the offset. Also, the A/D conversion timing when light emitting diode 1 lights up (
The lighting signal latch 12 is connected to the arrow ↑) to latch the light output vJ.

Subsequently, the digital subtraction circuit 14 subtracts the light output V11 when the light is turned off from the light output V8 when the light is turned on, and outputs a light output v2 corrected for the offset.

Thereafter, two or more operations are repeated to calculate the position data with high precision using the normal optical output with the offset removed.

In addition, in each of the above embodiments, the turn-off time is set before lighting up one light emitting diode 1 to compensate for offsets such as dark current (light output v
11).

Detects the offset at one timing within one cycle.

Alternatively, it may be configured to be performed once every several cycles, and subsequent subtractions may be performed using the value of − during the period in which the optical output v1□ is updated.

<Effects of the Invention> According to the present invention, there is provided a light emission control unit that controls lighting and extinguishing of a light emitting element at a predetermined timing, a light-off signal detection unit that detects a signal when the light-emitting element is turned off, and Since a lights-off signal storage section that stores the lights-off signal detected by the signal detection section and a subtraction circuit that subtracts the lights-off signal stored in the lights-off signal storage section from the lighting signal detected when the light emitting element is turned on, This has the advantage that offsets that cause errors can be removed from the lighting signal, and position data can be calculated with high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of essential parts of an optical encoder showing an embodiment of the present invention. FIG. 2 is a timing chart for explaining the operation of the embodiment shown in FIG. 1, and FIG. 3 is a block diagram of main parts of an optical encoder showing another embodiment of the present invention. FIG. 4 is a timing chart for explaining the operation of the embodiment shown in FIG. 3, and FIG. 5 is a characteristic diagram showing the light output detected by the light receiving element. 1. A light emitting diode (LED) serving as a light emitting element. 2. Light emission control section, 3. Light output detection section that serves as both the lighting signal detection section and the lights out signal detection section, 4a, 4b... Light receiving element, 5. Analog amplifier, 6. Sample that serves as the lights out signal storage section. & hold circuit, 7... subtraction circuit, 8... A/D converter. Patent Applicant Fanuc Co., Ltd. Agent Patent Attorney Chiki Saito Figure 1 Figure 3 Figure 2 Figure 4 VI Latte V+
VI
Vt figure 5

Claims (3)

[Claims] (1) In an optical encoder that has a lighting signal detection unit that detects an output signal of a light receiving element when a light emitting element is turned on, and calculates position data according to an output value of the detected lighting signal, the light emitting A light emission control unit that controls lighting and extinction of the light emitting element at a predetermined timing, a light-off signal detection unit that detects a signal when the light-emitting element is turned off, and a light-off signal detection unit that stores the light-off signal detected by the light-off signal detection unit. An optical encoder comprising: a lights-off signal storage section; and a subtraction circuit that subtracts the lights-off signal stored in the lights-off signal storage section from the lighting signal detected when the light emitting element is turned on. (2) The optical encoder according to claim 1, wherein the subtraction circuit performs subtraction using a lighting signal and a lighting-off signal that are analog data. (3) The optical encoder according to claim 1, wherein the subtraction circuit performs subtraction using a lighting signal and a lighting-off signal that are digital data.