JP4737612B2 - Encoder - Google Patents

Description

  The present invention relates to an encoder.

  For example, in an industrial machine such as an industrial robot, each component is operated by an actuator such as an AC servo motor, but the operation control is required to have high accuracy. As such an actuator position sensor and rotation angle sensor, an optical encoder is known which detects the position of the actuator and outputs it as a digital signal.

As will be described in detail later, this optical encoder normally passes light from an LED as a light emitting section through a rotating disk with a slit and inputs it to a light receiving element, converts the optical signal into a current signal, After being output as an analog signal, the digital signal is converted and output as a control signal to a control circuit (upper controller) such as an actuator.
JP 2005-156549 A

  However, the LED that forms the light emitting portion in the optical encoder is a life component having a characteristic that the light emission amount deteriorates when used for a long time, and the decrease in the light emission amount due to the deterioration is caused by the output analog signal. There has been a problem that when the signal is reduced (decrease in amplitude) and digital conversion is not performed correctly, a suitable output signal cannot be obtained. The present invention has been made in view of such a problem, and an object thereof is to correctly detect deterioration of an LED during operation of an optical encoder.

The encoder of the present invention (see, for example, the optical encoder 100 in the embodiment) changes the value of the current that flows through the light emitting unit according to the change in the amount of light emitted from the light emitting unit (see, for example, the LED 102 in the embodiment). A light emitting means driving circuit (for example, refer to the LED driving circuit 24 in the embodiment) for making the light emission amount of the light emitting means substantially constant, and a temperature detecting means for detecting the temperature of the light emitting means or its surroundings (for example, a temperature sensor in the embodiment) 26), and when the current value exceeds a predetermined current value and the temperature detected by the temperature detecting means is equal to or lower than a predetermined temperature, it is determined that the light emitting means is abnormal. An abnormality detection circuit (see, for example, the LED life detection circuit 30 in the embodiment). Furthermore, the light emitting means is preferably an LED.

  ADVANTAGE OF THE INVENTION According to this invention, the encoder which can detect the deterioration of a light source correctly can be provided.

First, a conventional optical encoder will be described as a premise for explaining an embodiment of the optical encoder of the present invention. Referring to FIG. 1, it is a block diagram showing an outline of the configuration of a conventional optical encoder 100. In this optical encoder 100, normally, two LEDs 102 are used as a light emitting unit, and light emitted from the LEDs 102 passes through the rotating disk 104 and enters the light receiving element 106. The rotating disk 104 is provided with slits at predetermined rotation angles. When the rotating disk 104 rotates and the LED 102 emits light when the slit is positioned on the optical path from the LED 102, light passes through. It is configured to enter the light receiving element 106. The light from the LED 102 that has entered the light receiving element 106 is converted into an electric current and output as an analog signal to each LED 102 via the amplifier circuit 108. This analog signal is converted into a digital signal by the digital processing circuit 110 and output to the host controller 112 side.

In the optical encoder 100, the digital processing circuit 110 cannot correctly recognize the analog signal when the signal becomes small. Therefore, in order to output a suitable digital signal, the analog signal output from the amplifier circuit 108 is constant and detailed. Needs to keep the amplitude of the output pulse current (hereinafter referred to as “analog signal”) constant. Therefore, it is necessary to keep the light emission amount of the LED 102 within a predetermined range. On the other hand, the LED 102 has a characteristic that its light emission amount decreases due to deterioration when it is used for a long time. In the optical encoder, the light emission amount decreases as the life time of the LED approaches, and the analog signal from the amplifier circuit 102 is reduced. Will decrease in amplitude. Although details will be described simultaneously in the embodiments of the present invention described later in detail, in the case of the conventional optical encoder 100 in order to avoid such a situation, the output signal from the light receiving element 106 is fed back to the LED drive circuit 114, By changing the forward current to the LED 102 in accordance with the change in the light emission amount of the LED 102, the light emission amount of the LED 102 can be kept constant, and as a result, the analog signal output from the amplifier circuit can be kept constant.

However, there is a limit to the control of the forward current to the LED 102 (see the description of the transistor 28 described later), and a forward current exceeding a certain level cannot be passed through the LED 102. Accordingly, when the deterioration of the LED 102 progresses and the light emission amount decreases by a predetermined value or more, the forward current increase limit to the LED 102 is reached, and the amplitude of the analog signal starts to decrease. A graph showing this state is shown in FIG. 2. FIG. 2A shows the relationship between time-LED forward current and FIG. 2B shows the relationship between time-analog signal amplitude. As shown in FIG. 2A, when the LED 102 deteriorates with time, the forward current increases in order to correct the decrease in the light emission amount with respect to the current. As a result, the amplitude of the analog signal is maintained at a constant value (Amax) as shown in FIG. As described above, the increase in forward current to the LED 102 is limited, and in FIG. 2A, if the LED 102 is used for a time t, the forward current Imax is reached, and thereafter, the time has passed with the maximum current. Therefore, as shown in FIG. 2B, the analog signal amplitude cannot be maintained at Amax with the time t when the forward current reaches Imax as a boundary, and the amplitude decreases with time. Then, when the analog signal amplitude is reduced to such an extent that the digital signal cannot be correctly recognized by the digital processing circuit 110 (time t1, amplitude A1 shown in FIG. 2B), it is determined that the LED life is reached, and the arrival of the amplitude A1 is detected. An alarm signal is output to the host controller 112 as “signal abnormality”. Thereby, the lifetime of the LED 102 is estimated.

However, in the case of the conventional optical encoder 100, it is estimated that the lifetime of the LED 102 is reached when the analog signal amplitude reaches a predetermined value or less. However, this is only an estimation, and the cause of the decrease in the analog signal amplitude is the LED 102. There are various factors such as malfunction due to noise, dust adhering to the rotating disk 104, failure of other electronic components, etc., and “signal abnormality” does not necessarily detect the life of the LED 102. Therefore, in order to determine the lifetime of the LED 102 in the conventional optical encoder 100, it is necessary to analyze the LED 102 in which the “signal abnormality” has occurred, and whether the LED 102 is approaching the lifetime during the operation of the optical encoder 100. Could not be confirmed.

Further, when it is desired to detect the life time of the LED 102 in advance, the forward current of the LED 102 is monitored, and when the forward current exceeds a predetermined value or when the maximum time (Imax in FIG. 2B) reaches a predetermined time. It is also possible to infer that the lifetime is over when the time elapses. However, since the light emission amount of the LED 102 decreases at a high temperature due to its temperature characteristics, it is unclear whether the increase in forward current is due to deterioration of the LED 102 or an increase in temperature. For example, FIG. 3 shows the relationship between temperature and LED forward current. In addition, the conventional optical encoder 100 is equipped with a temperature sensor 116 and has a function of outputting a “temperature abnormality” to the host controller 112 side when the sensor detects a predetermined temperature or higher such as a specification temperature. It was. However, the temperature sensor 116 in the conventional optical encoder 100 only outputs the information when a temperature higher than the specified temperature is detected.

The optical encoder of the present invention solves the drawbacks of the conventional optical encoder 100. Specifically, in the optical encoder of the present invention, when the forward current of the LED increases and approaches the lifetime, a means for informing the LED lifetime is provided in advance, and the LED of the LED is based on the temperature information of the temperature sensor. Means are provided for switching between a life-detectable mode and a non-detectable mode. The embodiment will be described below.

  Referring to FIG. 4, a schematic block diagram of an optical encoder 10 that is one embodiment of the present invention is shown. In this optical encoder 10, as in the conventional optical encoder 100 shown in FIG. 1, an LED is used as a light emitting unit, and light emitted from the LED 12 passes through the rotating disk 14 and enters the light receiving element 16. When the rotating disk 14 rotates and the LED 12 emits light when the slit is positioned on the optical path from the LED 12, the light passes through and enters the light receiving element 16. Further, the light from the LED 12 that has entered the light receiving element 16 is converted into an electric current, and is output as an analog signal to each LED 12 via the amplifier circuit 18. The analog signal is converted into a digital signal by the digital processing circuit 20 and output to the host controller 22 side.

The pulse signal output from the light receiving element 16 is input to the amplifier circuit 18 and is also fed back to the LED drive circuit 24. As outlined in the LED drive circuit 114 in the conventional optical encoder 100 described above, the LED drive circuit 24 changes the forward current to the LED 12 in accordance with the change in the light emission amount of the LED 12. Specifically, the signal from the light receiving element 16 is input to the feedback circuit 32, and the output voltage of the feedback circuit 32 is changed according to the change in the signal from the light receiving element 16 based on the change in the light emission amount of the LED 12. This output voltage is connected to the base terminal 28b of the transistor 28 as shown in FIG. The collector terminal 28 a of the transistor 28 is connected to the power source Vcc via a resistor R provided in the LED drive circuit 24. Further, the emitter terminal 28 c of the transistor 28 is connected to the LED 12. Therefore, if the voltage at the collector terminal 28a is known, the forward current value supplied to the LED 12 can also be detected. In particular,
LED forward current value = (power supply voltage Vcc−collector terminal voltage) / resistance R
Since the power supply voltage Vcc and the resistance R are constant values, the LED forward current value is detected by measuring the collector terminal voltage. The collector terminal voltage is
Collector terminal voltage = transistor collector-emitter saturation voltage + LED forward voltage
It is.

Here, for example, when the power supply voltage Vcc = 5.0V, the resistance R = 50Ω, the collector terminal voltage = 1.5V (LED forward voltage = 1.4V, collector-emitter saturation voltage = 0.1V) If you think about it,
LED forward current value = (5.0−1.5) /50=0.07.
Accordingly, the LED forward current can only flow up to 70 mA. Referring to the graph of FIG. 5, the LED forward current (upper left diagram), collector terminal voltage (upper right diagram), analog signal amplitude (lower left diagram), and light emission amount (lower right diagram) with respect to time under the above conditions are shown. . Referring to this figure, the initial value of the LED forward current is 10 mA, and the initial value of the collector terminal voltage is 4.5V. As the LED 12 deteriorates with use and the light emission amount decreases, the output voltage of the feedback circuit 32 decreases accordingly, and the collector terminal voltage also decreases (upper right diagram). Specifically, the collector terminal voltage is reduced to 1.5 V when time t elapses, and the LED forward current value increases to 70 mA, as can be seen from the above calculation formula (upper left diagram). As a result, while the forward current to the LED 12 increases to 70 mA, the light emission amount of the LED 12 is kept constant (lower right diagram), and as a result, the amplitude of the analog signal output from the light receiving element 16 is also kept constant. (Bottom left).

  Thereafter (after elapse of time t), when the LED 12 is further deteriorated, the collector terminal voltage becomes 1.5 V as the minimum value, and cannot be lowered any further (upper right figure), and the LED forward current maintains 70 mA. (Upper left). Therefore, the light emission amount of the LED 12 decreases as it deteriorates (lower right diagram), and the amplitude of the analog signal output from the light receiving element 16 also decreases (lower left diagram). If the LED 12 is used as it is, a signal that cannot be correctly recognized by the digital processing circuit 20 even if it is amplified by the amplifier circuit 18, and is simply output as “signal abnormality” (lower left diagram).

  Here, in the optical encoder 10 of the present invention, an LED life detection circuit 30 is provided. In this LED life detection circuit 30, a general-purpose voltage detection IC (not shown) is used. The input side is connected to the collector terminal 28 a and the output side is connected to the digital processing circuit 20. With such a configuration, the collector terminal voltage is constantly monitored. When a predetermined voltage is detected, for example, when the collector terminal voltage 1.5 V shown in the upper left diagram of FIG. A signal “H” is output to the digital processing circuit 20. The digital processing circuit 20 to which the signal is input recognizes this signal as a signal notifying the LED life and outputs an alarm notifying the LED life to the host controller 22 side. For example, in the example of the optical encoder 10 shown in FIGS. 4 and 5, the forward current of the LED 12 becomes 70 mA if the set voltage of the voltage detection IC of the LED life detection circuit 30 is set to 1.5V. At that time, an alarm that informs the life of the LED 12 is output. In addition, as shown in the upper right diagram of FIG. 5, if the collector terminal voltage reaches 1.5V, it will be held at the same voltage, so if the set voltage of the voltage detection IC is set to just 1.5V, even a little detection error will occur. If the collector terminal voltage reaches 1.5V, no alarm is output, or an alarm may be output after a long delay after reaching 1.5V, so the voltage set by the voltage detection IC is 1.5V ( That is, it is preferable to set a value larger than the minimum value of the collector terminal voltage by a predetermined value. In this case, an alarm is output at least when the forward current reaches 70 mA, slightly before the forward current to the LED 12 reaches 70 mA.

  After the alarm is output, the analog signal decreases, but a predetermined time is required until the “signal abnormality” described above (see t to t1 in the lower left diagram of FIG. 5). Therefore, it is possible to secure a sufficient time for replacing the entire LED 12 or the optical encoder 10 during the predetermined time, and it is possible to execute smooth maintenance work without stopping the entire system as a “signal abnormality”. it can.

Further, as described above, in the conventional optical encoder 100, the light emission amount decreases when the temperature characteristic of the LED is high, so the decrease in the light emission amount is due to the deterioration of the LED (the lifetime is approaching). It is difficult to determine whether it is due to high temperature or not. In the optical encoder 100 of the present embodiment, the output side of the temperature sensor (temperature sensor IC) 26 is connected to the digital processing circuit 20 to acquire temperature information of the LED 12 from the temperature sensor 26 or the vicinity thereof, and the acquired temperature. The digital processing circuit 26 outputs a control signal to the LED life detection circuit 30 side so that the LED life detection circuit 30 is effectively operated only when is less than a predetermined value. Therefore, when the above-described alarm is output from the digital processing circuit 26 to which the signal for informing the life of the LED 12 is input by the LED life detection circuit 30, it can be determined that the life time of the LED 12 is approaching. That is, according to the present optical encoder 100, it can be distinguished whether it is due to the lifetime of the LED 12 or due to a decrease in the amount of light emission due to the temperature characteristics of the LED 12, and in advance during the operation of the optical encoder 10. It becomes possible to detect that the lifetime of the LED 12 is approaching. For example, when the digital processing circuit 20 outputs a control signal for enabling the LED life detection circuit 30 only when the temperature information is 40 ° C. or less to the LED life detection circuit 30 side, the LED life detection circuit is used when the temperature is 40 ° C. or more. 30 becomes invalid, and the LED life detection circuit 30 can be enabled only when the temperature is lower than 40 ° C.

As described above, one of the embodiments of the optical encoder of the present invention has been described. However, the optical encoder of the present invention is not limited to this. For example, when it is desired to know the lifetime of the LED early, The voltage value of the voltage detection IC and the temperature threshold value of the temperature sensor can be changed according to demands such as when it is desired to use the battery until it reaches the end of its lifetime.

It is a schematic block diagram of the conventional optical encoder. (A) is a graph showing the relationship of time-LED forward current, and (b) is a graph showing the relationship of time-analog signal amplitude. It is a graph which shows the relationship of temperature-LED forward current. 1 is a schematic block diagram of an optical encoder of the present invention. It is the graph which showed an example of the information relevant to LED lifetime detection in the optical encoder of this invention, an upper left figure is time-LED forward current, an upper right figure is time-collector terminal side voltage of a transistor, (c) is time. -Analog signal amplitude output from the amplifier circuit, (d) shows the correlation between time-LED light emission.

Explanation of symbols

10 Optical encoder 12 Light emitting means (LED)
14 Rotating disk 16 Light receiving element 18 Amplifying circuit 20 Digital processing circuit 22 Host controller 24 Light emitting means driving circuit (LED driving circuit)
26 Temperature detection means (temperature sensor)
28 Transistor 30 Light emitting means life detection circuit (LED life detection circuit)
32 Feedback circuit

Claims (2)

A light emission means driving circuit for making the light emission amount of the light emission means substantially constant by changing a current value flowing through the light emission means according to a change in the light emission amount of the light emission means;
Temperature detecting means for detecting the temperature of the light emitting means or its surroundings;
An abnormality detection circuit that determines that the light emitting means is abnormal when the current value exceeds a predetermined current value and the temperature detected by the temperature detection means is equal to or lower than a predetermined temperature; The encoder characterized by having. The encoder according to claim 1, wherein the light emitting means is an LED.

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