Position detecting circuit

Abstract: A position detecting circuit for use in an apparatus for performing position control such as an original read­ ing apparatus is disclosed. In the position detecting circuit according to the present invention, emitted light from a light emitting device is received by a CCD image sensor and a peak value of the output signal waveform of the CCD image sensor is detected. Then, the photosensing position of the CCD image sensor is identified according to the position of the peak value in the output signal waveform. The position of a moving member is determined by the photosensing position of the CCD image sensor, whereby the position detecting system is simplified in structure and enhanced in detecting accuracy.

Description: The invention relates to a position detecting apparatus, particularly for an apparatus performing position control, comprising a light emitting device attached to a moving member and a CCD image sensor in the form of a one-dimensional array attached to a fixed member disposed to confront said moving member, a signal processing circuit for processing a signal waveform output from said CCD image sensor, and a counter counting in synchronism with a reading clock signal (first synch signal i), being stopped counting by an output signal of the signal processing circuit, and being reset by a reset signal (second synch signal h) for generating an address designating the current position of said moving member. Such an apparatus is already known from GB-A-21 57 426. Fig. 1 shows the principle of detection performed in a further prior art example of a position detecting system. Referring to the figure, reference numeral 18 denotes a light emitting device, 19 denotes a rotating member, 20 denotes a slit made in the rotating member, 21 denotes a photosensor device, and 22 denotes a counter. Below will be described operation of the above mentioned arrangement. Light emitted from the liaht emitting device 18 is introduced through the slits 19 made in the rotating member 20 into the photosensor device 21 and thereby converted into an electric signal. The electric signal becoming a pulse signal is counted in number of pulses by the counter 22 and thereby the position of the rotating member is detected. The detecting method in the prior art position control system has been of the type to pick up a signal carrying information about position and it therefore has had a mechanical arrangement in the detecting portion. Consequently, there have been such problems that the system requires complex and large size structure and its detecting accuracy is low. The present invention was made to solve the above mentioned problems. Accordingly, an object of the present invention is to provide a position detecting apparatus capable of directly detecting a current position of a moving member, simplifying the structure of the signal processing circuitry for detecting the position, and, further, capable of electric position detecting with high accuracy. The position detecting apparatus according to the invention is characterized in that the signal processing circuit includes a low-pass filter for deriving an envelope waveform from the output of said CCD image sensor, a first and a second level comparator, the first level comparator receiving the output of the low-pass filter and enabling the second level comparator only if the output of the low-pass filter is larger than a first reference voltage, a differentiator for differentiating the output of said low-pass filter, and the second level comparator outputting an output pulse to stop the counting operation of the counter when the output voltage of said differentiator is larger than a second reference voltage. Preferable embodiments are defined in the dependent claims. Fig. 1 is a block diagram showing an arrangement of a prior art position detecting apparatus; Fig. 2 is a block diagram showing an arrangement of the position detecting circuit of an apparatus according to an embodiment of the present invention; Fig. 3 is a drawing showing an arrangement of a detecting portion in an embodiment of the present invention; Fig. 4 is a detailed circuit diagram for the block diagram of Fig. 2; Fig. 5 is a diagram showing partial waveforms of the waveforms obtained at outputs of each of circuits; Fig. 6 is a diagram showing waveforms at the detecting portion; Fig. 7 is a timing chart showing operating principle of Fig. 4; and Fig. 8 is an explanatory drawing of operating principle of the detecting portion. An embodiment of the present invention will be described with reference to the accompanying drawings. Referring to Fig. 3, reference numeral 1 denotes a CCD image sensor attached to a fixed member 17, 13 denotes a moving member, 14, 15, and 16 denote a light emitting device, a reflecting mirror, and a condenser lens, respectively, attached to the moving member 13, and 17 denotes the fixed member. Fig. 2 is a block diagram showing an arrangement of the present invention, in which reference numeral 2 denotes an amplifier for amplifying a signal output from the CCD image sensor 1, 3 denotes a buffer supplied with an output signal of the amplifier 2, 4 denotes a detector such as a low-pass filter (L.P.F.) for obtaining an envelope on an output signal of the buffer 3, 5 denotes an inverting amplifier for amplifying an output signal of the detector 4, 6 denotes a first level comparator for comparing an output signal of the inverting amplifier 5 in voltage level with a first reference input, 7 denotes a differentiator for differentiating an output signal waveform of the inverting amplifier 5, 8 denotes a second level comparator for comparing an output signal of the differentiator 7 in voltage level with a second reference input, 9 denotes a flip-flop (hereinafter to be called "F/F") for synchronizing an output signal of the second level comparator 8 with a first sync signal, 10 denotes an address counter, 11 denotes a latch for receiving an address output from the address counter 10, and 12 denotes a buffer for receiving data output from the latch 11. Fig. 4 is a detailed circuit diagram for the block diagram of Fig. 2, Fig. 5(b) to Fig. 5(g) are diagrams showing partial waveforms of the waveforms obtained at outputs of each of circuits in Fig. 4, Fig. 6 is a diagram showing waveforms at a detecting portion in Fig. 4, Fig. 7 is a timing chart showing operations of Fig. 4, and Fig. 8 is an explanatory drawing of operating principle of the detecting portion. Referring to the detecting portion with a structure as shown in Fig. 3, the light emitted from the light emitting device attached to the moving member 13 is reflected by the reflecting mirror 15 provided to save the distance of the optical path, changed into a spotlight by being passed through the condenser lens 16, and thrown on the photosensing surface of the CCD image sensor 1. The CCD image sensor 1 irradiated by the spotlight senses the light and outputs a video signal. In this video signal, a peak value appears at the portion corresponding to the photosensing portion. The video signal with the peak value is amplified in signal amplitude by the amplifier 2 and input to the detector 4 through the buffer 3. Since the detector 4 operates as a low-pass filter (L.P.F.), the high-frequency portion of the input signal is removed and thereby an envelope signal (c) is obtained. The signal (c) is amplified in amplitude by the amplifier 5 so that the signal processing in the later stages may be performed steadily and input to the detecting portion. Here, the output (d) of the inverting amplifier 5 is first compared in voltage level with the first reference input by the first level comparator 6, whereby an output (e) at a TTL level having "H" value only at the portion of the signal (d) higher in voltage than the first reference input is obtained. On the other hand, the signal (d) input to the differentiator 7 is turned into a differentiated waveform (f) as shown in Fig. 5(f) and supplied to the subsequent second level comparator 8, and therein, compared in voltage level with the second reference input 2. Thereby, an output (g) at a TTL level having now "L" level only at the portion of the signal (f) higher in voltage than the second reference input is obtained. At this time, the output signal (e) of the first level comparator 6 serves as an output enable signal for the second level comparator 8, and therefore, the second level comparator 8 operates as the level comparator only while the signal (e) is "H" to provide the signal (g). The signal (g) is supplied to the subsequent F/F 9 and thereby synchronized with the first sync signal and input to the latch 11 as a latch signal. Meanwhile, the address counter 10 is reset by the second sync signal and the counter is operated to count the first sync signal serving as the clock. Its output is supplied to the latch 11 as address data of 12 bits. Although the 12-bit address data are being always supplied to the latch 11, the instant the latch signal (gl) supplied from the F/F 9 becomes "L", the data are latched in the latch 11, and passed through the buffer 12 in the subsequent stage and output to the control system subsequent thereto at the timing of the second sync signal. The 12-bit address data latched in the above described manner corresponds to the peak value of the video signal output from the CCD image sensor 1, i.e., the address of the photo sensing portion of the CCD image sensor 1, and the position on the moving member can thus be obtained by the 12-bit digital address data. Although, in the above described embodiment, the CCD image sensor was attached to the fixed member and the light emitting device was attached to the moving member, the light emitting device may be attached to the fixed member and the CCD image sensor may be attached to the moving member. Also a circuit configuration in which operational amplifiers are used for the detector (L.P.F.) and the differentiator in the position detecting circuit may be practicable. Further, the embodiment of this invention was described above as to its application to an image reading apparatus, but similar effects will be obtained if it is applied to a position detecting circuit in equipment requiring position control such as an apparatus in which scanning with an electron beam is performed for detecting the current position. It is also possible to detect a quantity in a rotating motion as a change in position by converting the rotating motion into a straight-line motion mechanically or electrically. Although a CCD image sensor and a light emitting device were used in the detecting portion, similar effects will be obtained without using them but by the use of a device providing a detected signal with a peak value in combination with a detecting portion. Further, it will be possible to arrange the address data to be provided in arbitrary number of bits.

Claims: Position detecting apparatus, particularly for an apparatus performing position control, comprising a light emitting device (14) attached to a moving member (13); a CCD image sensor (1) in the form of a one-dimensional array attached to a fixed member (17) disposed to confront said moving member (13); a signal processing circuit for processing a signal waveform output from said CCD image sensor (1); and a counter (10) counting in synchronism with a reading clock signal (first synch signal i), being stopped counting by an output signal of the signal processing circuit, and being reset by a reset signal (second synch signal h) for generating an address designating the current position of said moving member (13); characterized in that said signal processing circuit includes a low-pass filter (4) for deriving an envelope waveform from the output of said CCD image sensor (1); a first and a second level comparator (6, 8), the first level comparator (6) receiving the output of the low-pass filter (4) and enabling the second level comparator (8) only if the output of the low-pass filter (4) is larger than a first reference voltage; a differentiator (7) for differentiating the output of said low-pass filter (4), and the second level comparator (8) outputting an output pulse to stop the counting operation of the counter (10) when the output voltage of said differentiator (7) is larger than a second reference voltage. Position detecting apparatus according to claim 1, wherein light emitted from said light emitting device (14) is reflected by a reflecting mirror (15) and passed through a condenser lens (16) to the photosensing surface of said CCD image sensor (1). Position detecting apparatus according to claim 1 or 2, wherein the CCD image sensor (1) is attached to said moving member (13) instead of a light emitting device (14) and a light emitting device (14) is attached to said fixed member (17) instead of the CCD image sensor (1).

Inventors: TACHIBANA MIYUKI C O MITSUBISH, TACHIBANA MIYUKI C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1989
Main classification: G01D5
IPC codes: G01D5, G05D3