JPS622690Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to an optical index (photomark) reading device for reliably detecting a reference mark position when dynamically balancing a rotating body, for example.

When electrically reading the reference position of a rotating body, the configuration shown in FIG. 1 is usually used. First, an optical identification mark such as an index line is placed on the rotating body, and this is detected by a photoelectric detector. If the drive motor for the rotating body is a pulse motor, a pulse corresponding to the stop position θ is given to the motor to stop it at the desired position.
It goes without saying that the accuracy of the stop position depends on the rotation angle of the motor due to one pulse, but it is first necessary that the reference position pulse be applied without malfunction.

In the conventional method of photoelectrically detecting the reference position (0°) mark of a rotating body, the mark discrimination threshold is semi-fixed, so it depends on various factors such as the sharpness and reflectance of the mark and the smoothness of the background. The reality is that it is difficult to stably detect marks while keeping the same threshold value. To explain this situation more specifically, when a photomark is detected in the arrangement shown in 1 in Fig. 1, the electrical output signal will be as shown in Fig. 1 2 and 3, respectively, depending on the contrast of the specimen. If the signal No. 2 is detected at the level _L2 of No. 3, a noise signal N as shown in FIG. 4 is generated, which may cause malfunction. Conversely, if the signal of 3 is detected at the level of L ₁ of 2, not only noise but also the photo mark S
I can't even get a signal.

FIG. 2 is a block diagram showing the main parts of a known conventional photoelectric detection electronic circuit, in which 1 is a detector, 2 is a preamplifier, 3 is a comparator circuit, and 4 is a threshold value setting potentiometer. (variable resistance). The threshold setting potentiometer of No. 4 has the trouble of having to be adjusted to the optimum state each time to prevent malfunctions when the skin condition of the test object changes.

Conventionally, in order to solve this drawback, as shown in the block diagram of FIG. 3, a circuit 5 for storing the peak value of the signal is provided, and the output of this storage circuit is attenuated by a certain percentage, and the output of the next stage comparison circuit 3 is attenuated. It has been proposed to provide this as a discrimination threshold and extract the mark signal of the detector. In this case, the threshold value KAp (K: constant, 0<K<1) of 5 in FIG. 1 corresponds to this signal. FIG. 5 shows an embodiment of the peak value storage circuit in FIG. Fifth
In the figure, the detector 1 and the preamplifier 2 are omitted and not shown. In the two sets of blocks surrounded by chain lines, the first stage 5 is a peak value storage circuit, and the second stage is a comparison circuit. The peak signal is temporarily held in a capacitor C, outputted from the capacitor C, and entered into a comparator circuit 3 where it is compared with the input signal at the point.

However, these conventional methods have the drawback that sufficient comparison accuracy cannot be expected. This invention is an attempt to solve these problems. Namely, the average value of the background signal A is stored, the average value is subtracted from the signal A (A-), and the signal is amplified to the required signal level. This is a major feature of this invention, as it is designed to be input to the circuit. FIG. 4 is a block diagram showing its basic configuration, in which 6 represents an average value storage circuit, 7 represents a subtraction circuit, and 8 represents an amplifier. As shown in FIG. 1, the mark signal Ap includes the average value of the background signal, and as the proportion thereof increases, the noise margin decreases. Therefore, the remaining signal after subtracting the signal has an improved signal-to-noise (S/N) ratio. Since this signal is amplified to a required signal level and then input to the circuit shown in FIG. 3, it is possible to detect the mark signal reliably. That is, the present invention is a method of subtracting the average value of the detector output and the output of each moment (peak value, etc.), and the peak value can be extracted with good accuracy.

When detecting photomarks on objects,
The sharpness and reflectance of marks and the smoothness of the background depend on various factors such as color, and it has been difficult to detect marks stably under a wide range of conditions.However, this invention tests the threshold for distinguishing marks. This drawback has been corrected by automatically changing the threshold according to the body, eliminating the need to adjust the threshold each time the test specimen changes, making the positioning device easier to handle and more reliable. can.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the configuration of a rotary positioning device using the photomark photoelectric detection method, Fig. 2 is a block diagram showing the main parts of the electronic circuit for conventional photoelectric detection, Fig. 3 is a diagram showing the peak signal storage circuit output by a comparator. FIG. 4 is a block diagram showing the structure of the present invention; FIG. 5 is an electronic circuit diagram showing an example of the main part of FIG. 3. 1...Detector, 2...Preamplifier, 3...Comparison circuit, 4...Threshold value setter, 5...Peak value storage circuit, 6...Average value storage circuit, 7...Subtraction Circuit, 8...amplifier.

Claims (1)

[Scope of utility model registration request] It has a photoelectric detector that detects a photomark, a comparison circuit that compares its output with a reference signal, and a circuit that stores a peak value of the output of the photoelectric detector,
The reference signal level of the comparator circuit is automatically calibrated to an attenuation value of a certain percentage by the output of this peak value storage circuit, and in a device that detects only the output equal to or higher than the reference signal level as a photomark signal, photoelectric detection is possible. A circuit for calculating and storing the average value of the photoelectric detector output and a circuit for outputting a difference signal between the photoelectric detector output and this average value output are provided between the detector and the peak value storage circuit, and this difference signal is used as the An optical index reading device characterized in that the input is input to a peak value storage circuit.