Photoelectric switch

Abstract: A light projecting circuit of a photoelectric switch includes a light projecting element (2), a driver circuit (1, 3) for driving the light projecting element by use of pulses, and a change-over switch (4) for increasing or for decreasing an amount of light emitted from the light projecting element. With this provision, in an operation to adjust optical axes, the change-over switch can be used to increase the amount of the emitted light. Consequently, the position of the projected light beam can be easily confirmed.

Description: Field of the Invention The present invention relates to a photoelectric switch associated with optical fibers in which a projected light is introduced to a sense position by means of an optical fiber and a transmitted light or a reflection light thereof is delivered from the sense position to a light receiving element by use of an optical fiber. Description of the Prior Art Heretofore, in a light projecting circuit of an photoelectric switch, a light-emitting diode (LED) is used as a light projecting element. The LED is connected to a resistor for limiting a current flowing therethrough and a transistor as a driver thereof. The transistor has a base, which is supplied with a pulse signal from an oscillator so as to be turned on and off in response thereto, thereby resultantly blinking the LED by use of the pulse signal. The photoelectric switch of this type can be used in a wide range of environmental temperatures ranging from -25°C to 55 °C. The LED is assigned with a rated current, which is decreased as the temperature is increased. In consequence, the driving current of the light projecting LED has a limit associated with a rated current developed at an upper limit of the environmental temperature. In the conventional photoelectric switch, the rated current obtained at the upper limit of the environmental temperature limits the light projecting current. Consequently, the amount of the light thus projected from the LED is not sufficient. Even when a red-light LED is employed, a position of a beam of lights is not easily determined and hence there has been a problem that a considerably long period of time is necessary to align a light axis, for example, in a light receiving section. On the other hand, in a photoelectric switch employing optical fibers in which the fibers connect a sense position to a sensor unit, for example, as shown in FIG. 6, a light projecting element 6 of a sensor unit 101 is intermittently driven (with pulsated signals or pulses) by means of an oscillator circuit 103 so as to deliver a light emitting output from the light emitting element 6 to a light projecting optical fiber 7. Disposed to oppose an end surface of the optical fiber 7 is an end surface a light receiving optical fiber 8. Through the optical fiber 8, a light signal is delivered so as to be sensed by a light receiving element 9, which converts the light signal into an electric signal to be processed through an amplifier circuit 106, a detection circuit 107, and a waveform shaping circuit 108. The electric signal is thus converted into a rectangular wave to be outputted as an object sense signal via an output circuit 109 and to an indicator lamp 110, which thus indicates a sense state of an object. In the conventional photoelectric switch using optical fibers, since the optical fiber has a small diameter and is flexible, such a photoelectric switch is arranged in a position where the ordinary photoelectric switch not employing the optical fiber cannot be easily installed. In this arrangement, the optical fibers 7 and 8 are extended from the sensor unit 101. With the provision of this configuration in which an optical system of the photoelectric switch is constituted with optical fibers having a small diameter, it is possible to sense a fine or very small object. However, in the photoelectric switch adopting the optical fibers as described above, since the end portions of the optical fibers 7 and 8 are separated from the sensor unit, in an alignment of optical axes of the optical fibers and in a position alignment to adjust a distance to an object, it is necessary to confirm the blinking state of the indicator lamp 110 of the sensor unit 101 disposed at a location separated from the end portions of the optical fibers 7 and 8. Consequently, when the sensing position (associated with the end positions of the optical fibers) is apart from a location of the sensor unit or when a fine adjustment is required in the setting of the apparatus, there has been a disadvantage that the adjustment takes a long period of time. A device having the features of the preamble of claim 1 is known from MODERN ELECTRONIC CIRCUITS REFERENCE MANUAL McGraw-Hill, J. Markus, p300, "Light transmission checker" SUMMARY OF THE INVENTION It is therefore an object the present invention to provide a photoelectric switch in which an amount of light is increased when adjusting an optical axis to facilitate an alignment of a beam position. A technical problem to be solved in accordance with the present invention devised to cope with the problems of the conventional photoelectric switch employing optical fibers is to confirm an operation state at end portions of the optical fibers. The invention is as defined in claim 1. In accordance with the present invention, when aligning optical axes of the optical fibers, the light projecting element is intermittently driven by the light projecting means and then the amount of light attained from the light receiving optical fiber is determined for each first predetermined period by use of the deciding means so as to vary the number of light emitting pulses of the light projecting element based on the obtained light amount. In consequence, as the optical axes approach the aligned positions in the optical axis alignment, the intensity of the light beam emitted from an end surface of the light projecting fiber is increased. The deciding means favorably comprises an integrator circuit for integrating the signal outputted by the light receiving element for each first predetermined period and a comparator circuit for comparing the output from the integrator circuit with a predetermined threshold value. The light projecting circuit includes an oscillator circuit for oscillating a signal at a second predetermined period, a frequency divider circuit for a frequency of the oscillation output from the oscillator circuit, a synchronization circuit for producing a logical product or an ANDed result between an output from the comparator circuit of the decide means and the oscillation output from the oscillator circuit, and a driver circuit for driving the light projecting element based on the logical sum or ORed result obtained between an ouptut from the synchronization circuit and an output from the frequency divider circuit. The signal outputted by the light receiving element is integrated for each first predetermined period by use of the integrator circuit such that the comparator circuit produces a comparison output having a signal width associated with the amount of the receive light. By using the resultant signal as a gate signal, when an oscillation signal is supplied to the light projecting element, the number of emitted pulses per the unit time is altered, thereby changing the intensity of the light beam. The light projector circuit may also be constituted with a voltage/frequency (V/F) converter for converting a voltage representing the light amount determined by the decide means into a low-frequency signal having a frequency corresponding to the voltage and a driver circuit for driving the light projecting element based on an output from the voltage/frequency converter. The light projector means is provided with a voltage/frequency converter so that based on an amount of the receive light, the intermittent frequency of light at a visible level is changed by use of the voltage/frequency converter. In accordance with the present invention, as described above, when aligning optical axes at end portions of the optical fibers, the alignment of the optical axes can be checked depending on the amount of light emitted from the light projecting optical fiber or on the frequency of the blinking. Consequently, the indication on the sensor unit need not be confirmed for the purpose above. Namely, the confirmation can be accomplished by the light at the end portion of the optical fiber. As a result, the operation to align the optical axes of the optical fibers is facilitated, which leads to an advantageous effect that the operation can be easily confirmed. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and advantages of the present invention will become apparent by reference to the following description and accompanying drawings wherein: FIG. 1 is a block circuit diagram showing the constitution of the primary portion of a photoelectric switch using optical fibers as a first embodiment in accordance with the present invention; FIG. 2 is a timing chart showing operations of the switch of FIG. 1; FIGS. 3a to 3c are diagrams showing alignment states of optical axes at the ends respectively of the light receiving and projecting optical fibers; FIG. 4 is a block circuit diagram showing a photoelectric switch using optical fibers as a second embodiment in accordance with the present invention; FIG. 5 is a timing chart showing operations of the switch of FIG. 4; and FIG. 6 is a block circuit diagram schematically showing a conventional photoelectric switch using optical fibers. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, description will be given of an embodiment of a photoelectric switch according to the present invention. FIG. 1 is a block diagram showing a photoelectric switch employing optical fibers as a first embodiment in accordance with the present invention. As can be seen from this configuration, a photoelectric switch 10 employing optical fibers includes a circuit block 101 operative in the ordinary mode to detect presence or absence of an object, an operation indicator lamp 110 to indicate operations thereof, and a circuit block 20 to be operated to align optical axes. The change-over between the ordinary mode and the optical axis alignment mode is accomplished by means of a change-over switch 5 arranged on a panel of the photoelectric switch. Either one of outputs from the circuit blocks 101 and 20 is fed to a light projecting element 6 depending on the state of the change-over switch 5. The light projecting element 6 emits a visible light in response to a signal produced from either one of the circuit blocks 101 and 20. The emitted light is fed to a light projecting optical fiber 7. Like in the case of the conventional example above, an end portion of a light receiving optical fiber 8 is disposed to oppose an end portion of the light projecting optical fiber 7. The light receiving optical fiber 8 is used to conduct the light from a sense region to a photoelectric switch 10. The optical fiber 8 is connected to a light receiving element 9 at other end portion thereof. A light emitted from the light projecting element 6 and obtained from the sense region is received by the light receiving element 9 so as to be converted therein into an electric signal. The light receiving element 9 delivers a resultant signal as an output therefrom to the ordinary-mode block 101 and to the optical axis alignment circuit block 20. The configuration of the ordinary-mode circuit block 101 is identical to that of the sensor unit (FIG. 6) of the conventional photoelectric switch employing optical fibers described above. In consequence, the constitution thereof is not shown in FIG. 1. A description will next be given of the optical axis alignment circuit block 20. This circuit block 20 includes an oscillator circuit 11 oscillating at a predetermined period. The oscillator 11 delivers an output to a frequency divider circuit 12 and a synchronization circuit 13. The frequency divider 12 divides the frequency oscillation output, for example, by four and supplies an output to a driver circuit 14. The light receiving element 9 produces a receive signal, which is then amplified by an amplifier circuit 15 so as to be fed to a synchronization circuit 16. The synchronization circuit 16 is supplied with the frequency divided output from the frequency divider 12 such that the amplified output is further delivered therefrom to an amplifier circuit 17 by using the frequency divided output as a gate signal. The amplifier circuit 17 generates an amplified output, which is supplied via an integrator circuit 18 to a comparator circuit 19. The comparator circuit 19 is provided with a predetermined threshold value Vref1 set thereto so as to supply the synchronization circuit 13 with a signal exceeding the level of the threshold value Vref1. Based on the comparison output as a gate signal, the synchronization circuit 13 creates a synchronization signal based on a logical product between the comparison output and the oscillation output, thereby delivering the resutant signal to the driver circuit 14. The driver circuit 14 produces a drive signal based on a logical sum obtained between the output from the frequency divider circuit 12 and the output from the synchronization circuit 13 so as to drive the light projecting element 6. Incidentally, the amplifier circuit 15, the synchronization circuit 16, the amplifier circuit 17, the integrator circuit 18, and the comparator circuit 19 constitute decide means for determining an amount of light received by the light receiving optical fiber 8 for each predetermined period. On the other hand, the oscillator circuit 12, the frequency divider circuit 12, the synchronization circuit 13, and the driver circuit 14 configure light project means for intermittently driving the light projecting element 6 by changing the number of pulses emitted therefrom for each unit period of time based on the determined light amount. Next, a description will be given of operations of this embodiment. Referring now to FIG. 2 the frequency of the oscillation output from the oscillator circuit 11 is divided by the frequency divider circuit 12 by four. Based on a logical sum computed between the frequency divided output and the output from the synchronization circuit 13 which will be described later, the driver circuit 14 drives the light projecting element 6. As shown in FIG. 3a in a zone of time T1 in which the optical axis at the end portion of the light projecting optical fiber 7 is not aligned to that of the light receiving optical fiber 8, the light receiving element 9 is supplied with few output signals. In consequence, the output from the amplifier circuit 17 develops a value in the neighborhood of zero. The integrator circuit 18 therefore produces an output, which is below the threshold value Vrefl of the comparator circuit 17. Resultantly, the light projecting element 6 is driven for each predetermined period only by the output from the frequency divider circuit 12. Namely, in this state, the light is emitted at a low level for the operator adjusting the optical axes. When an optical axis adjustment is conducted under this condition to substantially establish an alignment of the optical axes of the light projecting and receiving optical fibers 7 and 8 as shown in FIG. 3b, the output signal received from the light receiving element 9 is amplified through the amplifier circuit 15 and the synchronization circuit 16. This time zone is designated as T2 in FIG. 2 in which there is obtained from the amplifier circuit 17 an output amplified in association with the amount of the received light. The resultant signal is integrated through the integrator circuit 18. At a point of time t₂ when the integrated value exceeds the predetermined threshold value Vrefl, the comparison output is produced. In consequence, the synchronization circuit 13 outputs a signal developed when the comparison output matches with the oscillation output so as to supply the signal to the driver circuit 14. As a result, the amount of light emitted for each unit of time is increased, which enables the operator to recognize that the end portion of the light projecting optical fiber 7 emits the light with a higher intensity. Consequently, comparing with the state of FIG. 3a in which the optical axes are not aligned to each other, the operator can gradually establish a complete alignment of the optical axes. Furthermore, as can be seen from FIG. 3c, when the optical axes are finally aligned to each other (in a time zone T3), the amplifier circuit 17 generates an output at a higher level and hence the integration output becomes to be increased. In consequence, as indicated in the range between the points of time t₃ and t₄, the compartor circuit 19 produces an output with a wider signal width. In association therewith, the number of pulses of the oscillation output passing through the synchronization circuit 13 becomes to be greater. Resultantly, the number of driver pulses for each unit time is increased in the driver circuit 14. Namely, the operator adjusting the optical axes perceives the light having a higher intensity. As described above, the operator visually checks the intensity of light at the end portion of the light projecting optical fiber 7 to set the level of the amount of light to a higher level. Namely, without necessitating the confirmation of the state by means of the indicator lamp 110 or the like on the photoelectric switch, the optical axes can be appropriately adjusted only by use of the optical fiber portions. Although the embodiment employs the frequency divider 12 to divide the frequency of the original oscillation output by four, the division ratio or the divisor may be further increased so as to natually obtain a greater change in the amount of light emitted from the light projecting optical fiber 7 depending on the degree of the alignment between the optical fibers. Next, a description will be given of the second embodiment in accordance with the present invention. This embodiment is characterized in that in place of the amount of light emitted from the light projecting optical fiber, the period of the light emission to be intermittently driven is changed. FIG. 4 is a block diagram showing the constitution of the embodiment. The same constituent components of this configuration as those of FIG. 1 are assigned with the same reference numerals. The system of FIG. 4 also includes an ordinary-mode circuit block 101 and an optical axis alignment circuit block 21, which are changed over by means of a mode change-over switch 5 so as to supply driver and receive signals associated with light projecting and receiving elements 6 and 9, respectively. The circuit block 21 includes an amplifier circuit 22 to amplify a receive signal attained from the light receiving element 9. The amplifier circuit 22 supplies an output to a sample-and-hold circuit 23. This circuit 23 samples and holds an amplified output at a timing which will be described later so as to supply an output to an integrator circuit 24. The integrator circuit 24 integrates a received signal to supply a resultant signal to an adder circuit 25. In the adder 25, a predetermined reference voltage Vref2 is added to the integrated output so as to feed the result of the addition to a voltage/frequency (V/F) converter 26. The converter 26 converts a supplied voltage to a low-frequency signal having a frequency repetition of which is visible and which is associated with the value of the input voltage. The converted signal is delivered to a driver circuit 27 and the sample-and-hold circuit 23. Based on the received output, the driver circuit 27 drives the light projecting element 6. Referring next to timing charts of FIG. 5, a description will be given of operations of this embodiment. As shown in FIG. 3a, when the optical axes of the light projecting and receiving fibers are not aligned to each other, since the integrator circuit 24 does not receive any significant output, the V/F converter 26 directly receives the reference voltage Vref2 from the adder circuit 25. Resultantly , as indicated in a time zone T1 of FIG. 5, there is produced a low-frequency signal having a duty of, for example, 50%. The obtained signal is delivered via the driver circuit 27 to the light projecting element 6, which in turn emits lights. In a time zone T2 in which the optical axes are to be gradually aligned to each other, the light receiving element 9 obtains a light signal. The signal is passed via the amplifier circuit 22 to the sample-and-hold circuit 23. In consequence, at points of times t 11, t₁₂, etc., the output signal is held so as to be supplied to the integrator circuit 24. The integrator circuit 24 hence produces an output with an increased value. Namely, the V/F converter 26 generates a low-frequency signal having a frequency associated with a voltage obtained by adding the reference voltage Vref2 to the voltage outputted from the integrator circuit 24. This signal is delivered via the driver circuit 27 to the light projecting element 6, which is thereby driven to emit lights. Consequently, by visually checking the end portion of the light projecting optical fiber 7, the operator can recognize that the period of the driving operation is gradually reduced. In a state where the optical axes are aligned to each other as shown in FIG. 3c (time zone T3), the end portion of the light projecting optical fiber 7 blinks at a minimized period, thereby indicating that the axis alignment is completed. In accordance with the present invention, as described above, the axis alignment can be determined only by visually confirming the state of the end portions of the light projecting optical fiber 7. Although the blinking frequency is increased as the axis alignment approaches the completed state in this embodiment, it may also be possible to lower the blinking frequency for this purpose. In the respective embodiments above, the ordinary-mode circuit block and the optical axis alignment circuit block are disposed to be independent of each other; however, the circuit configuration can be naturally simplified by sharing such circuits as the oscillator circuit, the driver circuit, and the amplifier circuit.

Claims: A photoelectric switch having: a light projecting element (6); a light receiving element (9) for outputting a signal representing received light; a light projecting optical fiber (7) for introducing light emitted from said light projecting element to a sensing position; a light receiving optical fiber (8) for leading light from the sensing position to said light receiving element; a detecting circuit (106, 107, 108, 109) for sensing an object on the basis of a level of the signal outputted from said light receiving element; and deciding means (16, 18, 19, 23, 24) for determining an amount of light attained from said light receiving optical fiber; characterized in that said photoelectric switch has a means (20, 21) for an optical alignment, said means being activated by a signal indicating an optical alignment mode set by a mode switch (5), and comprising: light projection control means (11, 12, 13, 14, 25, 26, 27) for controlling said light projecting element so as to vary the time during which light is being emitted for a predetermined period from said light projecting element based on the amount of light determined by said deciding means. A photoelectric switch in accordance with claim 1 characterized in that said deciding means includes an integrator circuit (18) for integrating the signal outputted by said light receiving element for each first predetermined period and a comparator circuit (19) for comparing the output from said integrator circuit with a predetermined threshold value; and said light projection control means includes an oscillator circuit (11) for oscillating a signal at a second predetermined period, a frequency divider circuit (12) for dividing the frequency of the oscillation output from said oscillator circuit, a synchronization circuit (13) for operating the logical product between the output from said comparator circuit of said deciding means and the oscillation output from said oscillator circuit, and a driver circuit (14) for driving said light projecting element by use of the logical sum between the output from said synchronization circuit and the output from said frequency divider circuit. A photoelectric switch in accordance with claim 1 characterized in that said light projection control means includes: a voltage/frequency converter (26) for converting a voltage representing the amount of light determined by said deciding means into a low-frequency signal having a frequency associated with the voltage; and a driver circuit (27) for driving said light projecting element based onthe output from said voltage/frequency converter.

Inventors: HARA MASATO, IMAI KIYOSHI, MATSUI YUTAKA, MISUMI FUMIHIKO, UEDA MASAZUMI, HARA, MASATO, IMAI, KIYOSHI, MATSUI, YUTAKA, MISUMI, FUMIHIKO, UEDA, MASAZUMI, HARA, MASATO, C/O OMRON CORP., INT. PRO. CEN., IMAI, KIYOSHI, C/O OMRON CORP., INT. PRO. CEN., MATSUI, YUTAKA, C/O OMRON CORP., INT. PRO. CEN., MISUMI, FUMIHIKO, C/O OMRON CORP., INT. PRO. CEN., UEDA, MASAZUMI, C/O OMRON CORP., INT. PRO. CEN.
Applicants: OMRON TATEISI ELECTRONICS CO, OMRON CORPORATION
Application year: 1990
Main classification: H03K17
IPC codes: H04B10, H03K17