JP5657292B2 - Displacement detector - Google Patents

Description

  The present disclosure relates to a displacement detection apparatus that detects the amount of displacement (movement) of a diffraction grating (scale) using light interference, and more particularly to a technique for managing a light source.

  The lifetime of a displacement detection device that requires extremely reliability in the industrial equipment field is an important parameter that affects the operation of the device using the displacement detection device.

  In a displacement detection device equipped with a light source, there is an example in which the life of the displacement detection device is determined by the life of the light source. Generally, when the light source is a light emitting diode (LED), the lifetime is 3 to 70,000 hours, and when the light source is a semiconductor laser (laser diode: LD), it is used for 2 to 40,000 hours. In doing so, it was necessary to prepare maintenance parts (replacement parts) in anticipation of the time.

  In such an environment, the light source is used for an extremely long time. Therefore, for the purpose of improving the maintenance at the time of deterioration of the light source, the light source is supplied from a location away from the displacement detection device by an optical fiber, and a connector is provided at the connection portion between the optical fiber and the light source, so that the light source can be replaced. The structure that made it possible is generally made.

  As another example, for example, in Patent Document 1, an encoder as a position sensor receives a light emitting element, a rotating disk irradiated with light from the light emitting element, and light received from the light emitting element via the rotating disk. A configuration is described in which a light receiving signal is output in accordance with a moving position of a rotating disk in which a light receiving element is disposed so as to be relatively movable with respect to the light emitting element and the light receiving element (FIG. 1). reference). The encoder determines whether or not an abnormality has occurred in the received light signal, and corrects the received light signal to avoid an abnormal state of the received light signal when it is determined that an abnormality has occurred in the received light signal. When the amount of light emitted from the light emitting element is adjusted, a warning is given to prompt the user to replace the encoder. With such a configuration, when an abnormality occurs due to deterioration of the encoder over time, a warning for prompting replacement of the encoder is given, and it is possible to avoid stopping the drive device equipped with the encoder.

  Further, in Patent Document 2, an encoder as a position sensor is provided with a pattern including a light emitting element, a light transmitting portion, and a light shielding portion, and a rotating disk, and a light receiving element that receives light from the light emitting element via the rotating disk. A configuration is described in which a light receiving signal corresponding to the moving position of the rotating disk is output (see FIG. 1). This encoder has a time series monitor circuit that calculates the moving average value of the received light signal, and a value higher than the signal level of the received light signal that is output when the received light intensity of the light receiving element decreases and the measuring unit becomes unmeasurable. It has a current monitor circuit that monitors whether or not the moving average value has fallen below the set judgment value, and a replacement alarm generation circuit that issues a warning when the moving average value falls below the judgment value (see FIG. 2). ). With such a configuration, it is possible to predict an abnormality due to deterioration of the encoder and prompt the exchange of the encoder before measurement becomes impossible.

  In Patent Document 3, a light source unit that emits a light beam of a parallel plane wave is constituted by a light emitting element and a first collimator lens, and the light source unit and a second collimator lens fixed at a predetermined position of the encoder are used. It is described that the light source module is configured. The second collimator lens converts the light beam of the parallel plane wave into a light beam that converges or diverges, and the light source unit can be attached to and detached from the light source module as a whole (see FIG. 2). According to such a configuration, when a failure caused by a light source occurs in a device such as an encoder, the light source can be quickly and easily replaced from the outside without removing the encoder from the control system.

JP 2006-284521 A JP 2006-284520 A Japanese Patent Laid-Open No. 1996-082533

However, when the light source used in the displacement detection device has deteriorated due to its life, it is used when the light source is replaced or the displacement detection device itself is replaced as described in Patent Documents 1 to 3. The entire device stops. For example, when a semiconductor device such as a light emitting diode or a semiconductor laser is used as the light source of the displacement detection device, once the device is stopped, it takes one day for stable operation.
In addition, it is necessary to prepare a spare light source and displacement detector for replacement in advance.
Further, accuracy is required when the light source is replaced, and it is necessary to finely adjust the displacement detection device after replacing the light source.

  The present disclosure has been made in view of the above situation, and prevents the displacement detection device from being stopped due to the lifetime of the light source. Moreover, even if it stops, there is no substantial influence on the apparatus, and it is not necessary to have extra spare parts in stock.

  The displacement detection device disclosed in the present application includes a auxiliary light source as a backup in addition to the main light source, and includes means for outputting information on the light emission state of the main light source and the auxiliary light source to the outside. When it is determined that the life of the main light source is near by using the information on the light emission state of the light source, the light source is switched so that the sub light source becomes the main light source. Examples of the configuration disclosed in the present application include the following modes.

  A displacement detection device disclosed in the present application includes a substantially flat diffraction grating that diffracts light from a light source, light receiving means that receives light diffracted by the diffraction grating, a first light source as a main light source, and a second light source. And a control means for switching the light source so that the second light source becomes the main light source when it is determined that the life of the first light source is near.

  According to the above configuration, the life of the main light source can be recognized, and the light source can be switched quickly in order to use the sub light source as the main light source. Switching of the light source is performed without directly touching the displacement detection device based on the control of the control means.

  According to the present disclosure, it is possible to prevent the apparatus using the displacement detection apparatus from being stopped. Moreover, even if it stops, there is no substantial influence on the apparatus, and there is an effect that it is not necessary to have extra spare parts in stock.

It is explanatory drawing which is an example of the displacement detection apparatus with which this invention is applied, and shows the example at the time of using a light emitting diode for a light source. It is explanatory drawing which is an example of the displacement detection apparatus with which this invention is applied, and shows the example at the time of using a semiconductor laser for a light source. It is 1st Embodiment of the displacement detection apparatus with which this invention is applied, Comprising: It is a circuit diagram at the time of using a semiconductor laser for a light source. It is a graph which shows the time characteristic of LD drive current Iop and monitor current Im in a semiconductor laser. It is a modification of 1st Embodiment of the displacement detection apparatus with which this invention is applied, Comprising: It is a circuit diagram at the time of using a semiconductor laser for a light source and using a memory. It is 2nd Embodiment of the displacement detection apparatus with which this invention is applied, Comprising: It is a circuit diagram at the time of using a light emitting diode for a light source. It is an example of the graph which shows the temperature characteristic of a semiconductor laser. It is an example of the graph which shows the temperature dependence of the wavelength of a semiconductor laser.

Hereinafter, an example of an embodiment for carrying out the present invention will be described with reference to the accompanying drawings. The description will be given in the following order. In addition, the same code | symbol is attached | subjected to a common part in each figure, and the overlapping description is omitted or simplified.
1. 1. Example of displacement detection device First embodiment (light source driving circuit: example using a semiconductor laser)
3. Second Embodiment (Light Source Drive Circuit: Example Using Light-Emitting Diode)
4). 4. Switching method from main light source to sub light source Other additional functions

<1. Example of displacement detection device>
For example, a light emitting diode (LED) or a semiconductor laser is used as a light source (main light source and sub light source) used in the displacement detection apparatus to which the present invention is applied. The wavelength of light output from these light sources is assumed to be 300 nm to 1300 nm. This is because, in general, a large number of light emitting diodes and semiconductor lasers in the visible range to the infrared range are on the market and are easily available. It is desirable that the main light source and the sub light source have similar optical characteristics such as wavelength and light quantity. Desirably, the light source is preferably a coherent light source, and the wavelength range of the light is only an example, and is not limited to this example in terms of technical thought.

[Light source: Example of light-emitting diode]
FIG. 1 is an example of a displacement detection apparatus to which the present invention is applied, and shows a configuration example in the case where a light emitting diode is used as a light source.
For example, when the main light source 3M and the sub light source 3S used in the displacement detection apparatus 1 are light emitting diodes, the light from the main light source 3M or the sub light source 3S is converted into the target diffraction grating via the lens 4 as shown in FIG. 2 is incident. Then, the diffracted light obtained by diffracting incident light by the diffraction grating 2 is made incident on the fixed slit 5 and received by the array type light receiving element 6 (example of light receiving means). The interference signal obtained by the light receiving element 6 is output to relative position information output means (not shown).

[Light source: Semiconductor laser example]
FIG. 2 is an example of a displacement detection apparatus to which the present invention is applied, and shows a configuration example in the case where a semiconductor laser is used as a light source.
The displacement detection device 10 includes a grating interferometer that generates an interference signal of light diffracted by the diffraction grating 2. The grating interferometer includes a main light source 11M and a sub light source 11S, a polarization beam splitter (hereinafter referred to as “PBS”) 12, a λ / 4 phase plate 13, a lens 14, a PBS 15, mirrors 16 and 17, / 4 phase plate 18, mirror 19, λ / 4 phase plate 20, and mirror 21. Further, a beam splitter (hereinafter referred to as “BS”) 22, a λ / 4 phase plate 23, a PBS 24, light receiving elements 25 and 26 (examples of light receiving means), PBS 27, and light receiving elements 28 and 29 (light receiving means). Example).

  In FIG. 2, the light emitted from the main light source 11 </ b> M is reflected by the PBS 12, passes through the λ / 4 phase plate 13, is converted from linearly polarized light to circularly polarized light, and enters the PBS 15 through the lens 14. The PBS 15 divides the circularly polarized light into two lights of P wave polarized light and S wave polarized light orthogonal to the P wave polarized light. In this example, it is assumed that the P wave polarized light is transmitted to the mirror 16 and the S wave polarized light is reflected to the mirror 17. Instead of providing the λ / 4 phase plate 13, the PBS 12 may be inclined by 45 degrees with respect to the optical axis.

  The P-wave polarized light guided to the mirror 16 is incident on an arbitrary irradiation spot of the diffraction grating 2 and is diffracted into one-time diffracted light, and a part of the one-time diffracted light is incident on the λ / 4 phase plate 18. The P-wave one-time diffracted light transmitted through the λ / 4 phase plate 18 is reflected by the mirror 19 and transmitted again through the λ / 4 phase plate 18 to be converted into S-wave one-time diffracted light. The S-wave one-time diffracted light is incident on the irradiation spot of the diffraction grating 2, is diffracted into S-wave two-time diffracted light, is reflected by the mirror 16, and is incident on the PBS 15.

  On the other hand, the S-wave polarized light guided to the mirror 17 is incident on the irradiation spot of the diffraction grating 2 and diffracted into one-time diffracted light, and a part of the one-time diffracted light is incident on the λ / 4 phase plate 20. . The S-wave one-time diffracted light transmitted through the λ / 4 phase plate 20 is reflected by the mirror 21 and again transmitted through the λ / 4 phase plate 20 to be converted into P-wave one-time diffracted light. The P-wave one-time diffracted light is incident on the irradiation spot of the diffraction grating 2, is diffracted into P-wave two-time diffracted light, is reflected by the mirror 17, and is incident on the PBS 15.

  Each of the mirror 16 and the mirror 17, the λ / 4 phase plate 18 and the λ / 4 phase plate 20, and the mirror 19 and the mirror 21 described above are arranged at symmetrical positions with respect to the straight line connecting the diffraction grating 2 and the PBS 15.

  The S-wave two-time diffracted light reflected by the mirror 16 and the P-wave two-time diffracted light reflected by the mirror 17 are superimposed on the PBS 15 and incident on the BS 22. In the BS 22, the combined wave of the S wave twice diffracted light and the P wave twice diffracted light is guided to the λ / 4 phase plate 23 and the PBS 27, respectively.

  The two times diffracted light of S wave and P wave guided to the λ / 4 phase plate 23 is transmitted through the λ / 4 phase plate 23 to be converted into two times diffracted light of circularly polarized light whose rotation directions are opposite to each other. The converted wave of the two-time diffracted light is converted into linearly polarized light that is rotated by a phase change caused by the displacement of the diffraction grating 2. Then, it is divided into two by PBS 24 and is incident on light receiving element 25 and light receiving element 26, respectively. For example, an interference signal of a sin signal is obtained at the light receiving element 25 and a −sin signal is obtained at the light receiving element 26. Each of these obtained interference signals is output to relative position information output means (not shown).

  On the other hand, the PBS 27 is disposed with an inclination of 45 degrees with respect to the optical axis. The two-time diffracted light of the S wave and P wave guided to the PBS 27 is incident on the PBS 27 so that components in the 45 degree direction of the S wave and P wave become interference light, and the light receiving element 28 and the light receiving element 29, respectively. Is incident on. For example, a cos signal is obtained in the light receiving element 28 and a cos signal is obtained in the light receiving element 29. Each of these obtained interference signals is output to relative position information output means (not shown).

  When the main light source 11M and the sub light source 11S to be used are semiconductor lasers as in the displacement detection device 10, the light from the main light source 11M or the sub light source 11S is divided into two, and each enters the target diffraction grating 2. Let And it is good also as a structure which reads the change of the phase information of the diffraction grating 2 as displacement information (displacement signal) by superimposing the two light again and making it interfere.

  2 and 3 adjusts the optical axis so that a desired signal is output from the light receiving element to each of the main light source 11M and the sub light source 11S at the time of manufacture. Just keep it.

  The present invention has a configuration in which light emitted from a light source is incident on a diffraction grating to be measured as described above, and a displacement detection device that converts a displacement amount of the diffraction grating into light brightness and detects it with a light receiving element. Can adapt to. For example, it can be applied to a linear encoder or a rotary encoder.

<2. First Embodiment>
With reference to FIG. 3 and FIG. 4, a first embodiment of a displacement detection apparatus to which the present invention is applied will be described. This embodiment is an example in which a semiconductor laser is used as a light source.

  FIG. 3 is a circuit diagram of a light source driving circuit when a semiconductor laser is used as a light source, which is a first embodiment of a displacement detection apparatus to which the present invention is applied. FIG. 4 is a graph showing time characteristics of the LD drive current Iop and the monitor current Im in the semiconductor laser.

[Configuration example of light source drive circuit of displacement detector]
The light source drive circuit 30 of the displacement detection apparatus includes a main main light source 11M, a secondary light source 11S as a spare, auto power control circuits (hereinafter referred to as “APC circuits”) 31M and 31S, and a control unit 34. The APC circuits 31M and 31S and the control unit 34 are examples of control means.

  A main light source 11M using a semiconductor laser is packaged with a laser diode (hereinafter referred to as “LD”) which is a light emitting portion and a photodiode (hereinafter referred to as [PD]) which receives a part of light emitted from the LD. ing. The LD of the main light source 11M and the cathode of the PD are grounded, and the anode of the LD and the anode of the PD are respectively connected to the APC circuit 31M.

The APC circuit 31M is provided to control the light emission of the main light source 11M, and includes a transistor 32 that is an element that performs a switching operation and a current-voltage conversion unit (hereinafter referred to as “I / V”) that converts current into voltage. Part) 33). The input unit of the I / V unit 33 is connected to the anode of the PD of the main light source 11 M , and the output unit of the I / V unit 33 is connected to the base of the transistor 32. The emitter of the transistor 32 is connected to the anode of the LD of the main light source 11M.

  As with the main light source 11M, the sub-light source 11S is packaged with a laser diode (LD) and a photodiode (PD) that receives a part of light emitted from the LD. The LD and PD cathodes of the sub-light source 11S are grounded, and the LD anode and the PD anode are respectively connected to the APC circuit 31S.

APC circuit 31S is provided in order to control the light emission of the auxiliary light sources 11 S, similarly to the APC circuit 31M comprises a transistor 32, a current-to-voltage converter (I / V unit) 33. The input unit of the I / V unit 33 is connected to the anode of the PD of the sub- light source 11 S , and the output unit of the I / V unit 33 is connected to the base of the transistor 32. The emitter of the transistor 32 is connected to the anode of the LD of the sub light source 11S.

  In this example, an NPN bipolar transistor is used as the transistor 32. However, the transistor is not limited to this as long as it performs a switching operation. For example, various elements and circuits such as a PNP bipolar transistor and a field effect transistor can be applied. The internal configuration of the APC circuits 31M and 31S is also an example, and is not limited to this example.

  The control unit 34 performs overall control of the light source driving circuit 30 and, for example, an MPU (Micro-Processing Unit) is applied. The control unit 34 supplies drive power to the APC circuit 31M, and acquires the LD drive current Iop1 and the monitor current Im1 from the APC circuit 31M. Similarly, the drive power is supplied to the APC circuit 31S, and the LD drive current Iop2 and the monitor current Im2 are acquired from the APC circuit 31S. Then, the LD drive currents Iop1 and Iop2 and the monitor currents Im1 and Im2 are output to a display unit (not shown) as Iop value conversion information and Im value conversion information converted into a format that can be easily recognized by the operator. Further, when it is detected that the main light source 3M or the sub light source 3S is in the failure mode, an alarm signal is output to the display unit. Further, the control unit 34 controls each unit of the light source driving circuit 30 in accordance with an operation signal generated by an interface (hereinafter referred to as “I / F”) 35 in response to an operation of the operator.

  Generally, a semiconductor laser is packaged with a laser diode (LD) which is a light emitting portion and a photodiode (PD) which receives a part of light emitted from the LD. Since the PD receives a part of the light emitted by the LD, the light emission state of the LD is monitored, and the current generated here is called Im (monitor current). The APC circuit functions to control the LD drive current Iop (current supplied to the semiconductor laser) according to the magnitude of the monitor current Im.

  In the light source driving circuit 30 configured as described above, the monitor current Im1 output from the PD of the main light source 11M is supplied to the APC circuit 31M. In the APC circuit 31M, the I / V unit 33 converts the monitor current Im1 into a voltage, changes the voltage applied between the base and emitter of the transistor 32, and controls the LD drive current Iop1 output from the transistor 32 to control the main light source. Supply to 11M LD. The APC circuit 31M notifies the control unit 34 of the LD drive current Iop1 and the monitor current Im1 at this time. Since the sub light source 11S and the APC circuit 31S operate in the same manner, the description thereof is omitted.

  By such control, the main light source 11M and the sub light source 11S made of a semiconductor laser can emit light at a constant output. In the present embodiment, the APC circuits 31M and 31S are provided corresponding to the main light source 11M and the sub light source 11S, respectively, but two APC circuits may be combined into one. However, since the value of the monitor current Im of the semiconductor laser generally differs depending on the individual semiconductor laser, in order to output the same amount of light, it is desirable to individually provide an APC circuit and perform control according to the individual light source, Thereby, the light quantities of the main light source 11M and the sub light source 11S can be controlled more accurately.

  In this embodiment, only one auxiliary light source 11S is provided as a spare light source, but two or more spare light sources may be provided.

  As described above, when the semiconductor laser is driven, the light emission state of the light source can be recognized by the LD drive current Iop and the monitor current Im. In general, when a constant current continues to flow in a semiconductor laser, the light emission efficiency decreases with deterioration, and the light amount decreases. However, in the present embodiment, the value of the LD drive current Iop is controlled so that the light amount of the light source is made constant by the light amount control means using the APC circuit. Therefore, the deterioration of the light source cannot be determined from the light amount. Furthermore, since the light quantity is constant, the monitor current Im is also constant. Therefore, the deterioration of the light source cannot be determined from the value of the monitor current Im.

  On the other hand, as shown in FIG. 4, the LD drive current Iop supplied to the semiconductor laser increases with the deterioration of the light source. In general, in the case of a semiconductor laser having an LD drive current Iop of 50 mA and an output of about 5 mW, if it emits light continuously in an environment of 20 ° C., the LD drive current Iop increases by 1 to 4 mW in one year although there are individual differences. Can be confirmed.

  In general, the time when the LD drive current Iop is several percent higher than the initial value may be defined as the lifetime of the semiconductor laser. In consideration of the rise over time, it is set to allow a current with a margin to flow. Therefore, it is possible to control the LD drive current Iop supplied to the semiconductor laser to the extent that the APC circuit is controlled, and to output a certain amount of light to the semiconductor laser.

  By the way, the semiconductor laser has a change point of the ascending gradient of the semiconductor laser Iop per unit time (the broken line circled part in FIG. 4), in which the light emission efficiency suddenly decreases as the deterioration progresses. When entering the region related to this change point, that is, the failure mode, the LD drive current Iop starts to rise rapidly, reaches the control limit of the APC circuit, and the semiconductor laser Iop value becomes constant at the control limit value. Occurs and the monitor current decreases.

  In a general displacement detection device, the phenomenon of a decrease in the monitor current is confirmed for the first time, and an alarm signal is generated to prompt the replacement of the light source and the device before the semiconductor laser stops emitting light, that is, before it completely stops. However, some semiconductor lasers reach the control limit of the APC circuit (= the upper limit value of the LD drive current Iop) within a few hours when the LD drive current Iop starts to rise rapidly. In that case, the displacement detection device may stop completely without securing a sufficient time from the start of the output of the alarm signal.

  In this embodiment, since the auxiliary sub-light source 11S is provided, when the main light source 11M suddenly reaches the end of its life as described above, the light emitting environment is quickly switched, and the displacement in which the light source driving circuit 30 is mounted. It can prevent that a detection apparatus stops completely. Alternatively, even if the displacement detection device stops due to the life of the main light source 11M, the main light source 11M and the sub light source 11S are switched using communication without directly touching the displacement detection device, and the function (displacement signal detection) can be performed in a short time from the outside. ) Can be restored.

  Even when the displacement detection device is replaced together with the light source, it may be performed during the period in which the sub light source 11S emits light, and it is not necessary to stock spare parts for replacement in advance. In addition, the entire apparatus using the displacement detection device also has a time margin such as replacement of the displacement detection device in accordance with a regular maintenance period.

[Example of light source switching]
Hereinafter, determination of light source switching will be described.
The determination of light source switching may be performed by the control unit 34 or an instruction may be issued from the outside via the I / F 35. It is desirable to use the light source until the main light source 11M reaches the end of its life as much as possible. For example, a predetermined value may be set in advance for the LD drive current Iop1 that changes as the semiconductor laser deteriorates, and when the LD drive current Iop1 reaches the specified value, switching from the main light source 11M to the sub light source 11S may be performed. . However, since the LD drive current Iop of the semiconductor laser has a variation in the specified value, there is a possibility that the replacement time varies greatly depending on the individual.

[Example of preparing a memory for each light source]
As a means for eliminating the variation of each light source, a method of setting a predetermined value in advance for each light source can be considered. In this case, as shown in FIG. 5, the prescribed value of the LD drive current Iop of each light source is stored in each memory, and the switching time is determined based on the relative increase amount.

  FIG. 5 is a modification of the first embodiment, and shows a circuit diagram in the case where a semiconductor laser is used as a light source of a light source driving circuit and a memory is used. The light source drive circuit 40 shown in FIG. 5 is different from the light source drive circuit 30 (see FIG. 3) according to the first embodiment in that it has a memory. In the following, FIG. 5 will be described with a focus on differences from FIG. 3, and description of overlapping parts will be omitted.

  The light source drive circuit 40 of the displacement detector includes a memory 41M that stores a specified value (threshold value) of the LD drive current Iop1 of the main light source 11M, in addition to the components of the light source drive circuit 30 (see FIG. 3), and a sub-light source. A memory 41S that stores a prescribed value (threshold value) of the 11S LD drive current Iop2 is provided.

  The memory 41M and the memory 41S are non-volatile storage means, and for example, a semiconductor memory such as a flash memory is applied.

  The control unit 34 compares the LD drive current Iop1 output from the APC circuit 31M corresponding to the main light source 11M with the specified value of the LD drive current Iop1 stored in the memory 41M. When the value of the LD drive current Iop1 reaches the specified value stored in the memory 41M, the control unit 34 outputs an alarm signal to the display unit together with the Iop value conversion information and the Im value conversion information. When switching to the sub-light source 11S, the control unit 34 similarly monitors using the specified value of the LD drive current Iop2 stored in the memory 41S. Accordingly, it is possible to notify the operator of an appropriate switching time for each light source, reflecting variations in the LD drive current Iop for each light source.

  A more accurate light source switching time can be predicted by identifying the change point of the rising gradient of the LD drive current Iop per unit time. For example, when the value of the LD drive current Iop is acquired by sampling once per hour and differentiated by time, the differential value shows almost zero in normal times. On the other hand, in the failure mode, since the rising gradient of the value of the LD driving current Iop per unit time increases (see FIG. 4), the differential value increases, so the differential value may be regulated.

Further, the differential value in the failure mode can be used as a lifetime prediction of the light source.
Remaining life = ((upper limit of control in APC circuit) − (difference of current LD drive current Iop value))
/ (Increase gradient of LD drive current Iop per unit time)
This makes it possible to accurately predict the life of the light source. By switching from the main light source to the sub-light source during this time, the function (detection of the displacement signal) can be restored before the displacement detection device completely stops. it can.

  According to the first embodiment described above, the auxiliary light source as a spare is mounted in addition to the main light source, and means for outputting information on the light emission states of the main light source and the auxiliary light source to the outside is provided. Thereby, the lifetime of the main light source and the sub light source can be predicted more accurately.

  If it is determined that the life of the main light source is near, by switching the light source so that the sub light source becomes the main light source, the sub light source is caused to emit light in an emergency, thereby stopping the device using the displacement detection device. Can be prevented.

  Furthermore, since it is possible to switch from the main light source to the sub light source without directly touching the displacement detection device, it is not necessary to have extra maintenance parts in stock, and the maintenance cost can be reduced.

<3. Second Embodiment>
Next, a second embodiment of a displacement detection apparatus to which the present invention is applied will be described with reference to FIG. This embodiment is an example in the case where a light emitting diode (LED) is used as a light source.

  FIG. 6 shows a circuit diagram of a light source driving circuit when a light emitting diode is used as a light source, which is a second embodiment of the displacement detecting device to which the present invention is applied. In the following, FIG. 6 will be described with a focus on differences from FIG. 3, and description of overlapping parts will be omitted.

  When the light source is a light emitting diode, the light amount of the light emitting diode decreases as the light emitting diode deteriorates unless auto power control is performed by the APC circuit, as in the case of the semiconductor laser. However, in general, a light emitting diode does not have a light receiving element for monitoring like the photodiode (PD) in FIG. Then, a part of the light emitted by the light source LED is received by the PD, and the amount of light is controlled to be constant as in the case of the semiconductor laser based on the current (monitor current Im) generated here.

  In FIG. 6, a main light source 3M using a light emitting diode includes a light emitting diode (LED) which is a light emitting unit. The anode of the LED of the main light source 3M is connected to the APC circuit 51M, and its cathode is grounded.

  The APC circuit 51M is provided to control the light emission of the main light source 3M, and its basic configuration is the same as that of the APC circuit 31M. The APC circuit 51M includes a transistor 32 and a current-voltage conversion unit (I / V unit) 33. The cathode of the PD is connected to the power supply line connected to the collector of the transistor 32, and the anode of the PD is connected to the input unit of the I / V unit 33. Although an NPN bipolar transistor is used as the transistor 32, the present invention is not limited to this.

  Similar to the main light source 3M, the sub light source 3S includes a light emitting diode (LED) that is a light emitting unit. The APC circuit 51S is provided to control the light emission of the sub-light source 3S, and includes a transistor 32 and a current-voltage conversion unit (I / V unit) 33 as in the APC circuit 51M. Are the same.

  The control unit 34 supplies drive power to the APC circuit 51M, and acquires the LED drive current Iop1 and the monitor current Im1 from the APC circuit 51M. Similarly, drive power is supplied to the APC circuit 51S, and the LED drive current Iop2 and the monitor current Im2 are acquired from the APC circuit 51S. Then, the LED drive currents Iop1 and Iop2 and the monitor currents Im1 and Im2 are output to a display unit (not shown) as Iop value conversion information and Im value conversion information converted into a format that can be easily recognized by the operator.

  In the light source driving circuit 30 configured as described above, the monitor current Im1 output from the PD of the main light source 3M is supplied to the APC circuit 51M. In the APC circuit 51M, the I / V unit 33 converts the monitor current Im1 into a voltage, changes the voltage applied between the base and emitter of the transistor 32, and controls the LED drive current Iop1 output from the transistor 32 to control the main light source. Supply to 3M LED. The APC circuit 51M notifies the controller 34 of the LED drive current Iop1 and the monitor current Im1 at this time. Since the sub light source 3S and the APC circuit 51S operate in the same manner, the description thereof is omitted.

  In this way, the values of the LD drive currents Iop1 and Iop2 and the monitor currents Im1 and Im2 can be similarly extracted through the APC circuits 51M and 51S, and the switching time from the main light source 3M to the sub light source 3S is detected. Or it can be predicted.

  According to the second embodiment described above, the same operational effects as in the first embodiment can be obtained. In other words, the auxiliary light source as a spare in addition to the main light source is installed, and means for outputting information on the light emission state of the main light source and the sub light source to the outside is provided, so that the lifetime of the main light source and the sub light source can be predicted more accurately. can do.

  If it is determined that the life of the main light source is near, by switching the light source so that the sub light source becomes the main light source, the sub light source is caused to emit light in an emergency, thereby stopping the device using the displacement detection device. Can be prevented.

  Furthermore, since it is possible to switch from the main light source to the sub light source without directly touching the displacement detection device, it is not necessary to have extra maintenance parts in stock, and the maintenance cost can be reduced.

<4. Switching from main light source to sub light source>
Next, a method for switching from the main light source to the sub light source will be described.
The switching is performed based on an instruction through the communication unit (I / F 35) based on a determination by the control unit 34 or an external determination, but it is desirable to switch to the sub-light source so that the displacement detection device is not completely stopped.

  For example, in the case of the light source drive circuit 30 of FIG. 2, the LD drive current Iop1 and the LD drive current Iop2 that indicate the amount of emitted light are monitored, and the sum of the light amounts of the main light source 11M and the sub light source 11S is always constant. You may make it wrap and switch gradually (continuously). The overlap may be performed, for example, by adjusting drive power supplied from the control unit 34 to the APC circuit corresponding to the main light source and the APC circuit corresponding to the sub light source. The same applies to the light source drive circuit 40 of FIG. 5 and the light source drive circuit 50 of FIG.

  Further, the light source may be switched instantaneously at high speed in a time shorter than the sampling time for data acquisition by the APC circuit and the control unit of the displacement detection device. In some displacement detection devices using semiconductor lasers, interference between two types of light sources does not occur, but two types of interference signals may be received, so it may be better to switch instantaneously. .

  In other words, as shown in FIG. 2, the displacement detection device has a configuration in which the optical path lengths of the two lights are substantially equal, and the positional information error due to the two types of interference signals hardly affects. However, depending on the principle of the displacement detection device, the position information detected by the displacement detection device may slightly shift depending on the position and wavelength of the main light source and the sub light source. It is desirable to output to the outside through the communication means (I / F 35).

  At this time, error data generated at the time of switching may be corrected. That is, the count value obtained from the displacement signal jumps before and after the switching, resulting in a deviation. Therefore, the difference between the count values before and after switching may be obtained and corrected by subtracting the difference from the count value (error data) after switching.

  Of course, the displacement detection device may be temporarily stopped and switched by manual operation from the outside using the communication means (I / F 35). In any case, a displacement detector equipped with a main light source and a sub-light source can return its function (displacement signal detection) without touching the displacement detector directly, so that the loss of time after return is minimized. Can do.

<5. Other additional functions>
Next, other additional functions will be described with reference to FIGS.
FIG. 7 is an example of a graph showing the temperature characteristics of the semiconductor laser, and FIG. 8 is an example of a graph showing the temperature dependence of the wavelength of the semiconductor laser.

  The decrease in the signal output of the displacement detection device may be caused by dirt adhering to the vicinity of the light emitting unit in addition to the life of the light source. This is because when the displacement detector is used in a machine tool or the like, it is often used in the vicinity where dust or oil is generated, and the signal output decreases even though the light source emits light normally. Occurs.

  In this case, the value of the LD drive current (or LED drive current) Iop and the value of the monitor current Im described above are controlled to indicate normal values. Thus, an external communication means (I / F 35) can be used to issue an instruction from the operator to the control unit 34 to recognize a signal output abnormality and determine a cause other than a light source abnormality. For example, the sub-light source may be temporarily caused to emit light according to the operation of the operator, and it may be confirmed (phenomenon reproduction) whether the signal output is restored. Here, when the signal output is restored, the control unit 34 can determine that the vicinity of the light emitting unit of the main light source is dirty, and can output the diagnosis result to the outside through the communication means (I / F 35).

  Further, when the light source is a semiconductor laser, the control unit 34 can measure the LD drive current Iop of the light source and convert the measurement result as the temperature of the light source itself, so that the information may be output to the outside. FIG. 7 shows an example of the relationship between the laser current (LD drive current Iop) and the temperature of the semiconductor laser.

  If a temporal high-pass filter is applied to the LD drive current Iop converted value, relative temperature change information (for example, temperature change from a predetermined value) for a relatively short time, for example, 1 hour of the light source can be obtained. On the other hand, if a temporal low-pass filter is applied to the LD drive current Iop converted value, it can be used as information indicating the deterioration of the light source.

  Some recent displacement detection devices detect displacement with sub-nanometer accuracy, and these are displacement drifts caused by temperature changes of the displacement detection device itself and temperature changes of the displacement detection device due to temperature changes of the outside air. May be erased with correction. Since the converted value of the LD drive current Iop indicates the object temperature of the light source, it accurately indicates the temperature change of the displacement detection device that has occurred in a relatively short time. Therefore, the displacement drift (displacement amount) per unit temperature in advance. May be measured and used as erase information.

  Further, since the wavelength of the semiconductor laser accurately changes depending on the temperature of the element, the temperature may be converted from the temperature with reference to the relative temperature change information for a relatively short time. FIG. 8 is an example of a graph showing the relationship between the temperature and wavelength of a multimode semiconductor laser.

  As described above, it is also possible to obtain various information necessary for the displacement detection device other than the lifetime from information on the light emission state of the light source (for example, LD drive current, LED drive current, monitor current, etc.).

  The series of processes in the above-described embodiment can be executed by hardware, but can also be executed by software. When a series of processing is executed by software, it can be executed by a computer in which a program constituting the software is incorporated in dedicated hardware or a computer in which programs for executing various functions are installed. is there. For example, what is necessary is just to install and run the program which comprises desired software in a general purpose personal computer.

  As described above, the present invention is not limited to the above-described embodiments, and various other modifications and application examples can be taken without departing from the gist of the present invention described in the claims. Of course.

  DESCRIPTION OF SYMBOLS 1,10 ... Displacement detection apparatus, 2 ... Diffraction grating, 3M, 11M ... Main light source, 3S, 11S ... Sub-light source, 6, 25, 26, 28, 29 ... Light receiving element, 30, 40, 50 ... Light source drive circuit, 31M, 31S, 51M, 51S ... APC circuit, 34 ... control unit, 41M, 41S ... memory

Claims (1)

A substantially flat diffraction grating that diffracts light from the light source;
A light receiving means for receiving light diffracted by the diffraction grating;
A first light source which is a semiconductor laser as a main light source;
A second light source;
An auto power control circuit for driving the first light source and the second light source;
The laser drive current of the auto power control circuit is monitored, and when it is determined that the laser drive current has reached a specified value, a control unit having a function of outputting an alarm signal to the outside is provided,
Before the laser drive current for the first light source reaches the control limit of the auto power control circuit and the first light source causes a decrease in the amount of light, it is determined that the life of the first light source is near, and the second light source is used as the main light source. to have the line switching of the light source, so that the sum of the amount of the light intensity and the second light source of the first light source is constant, the displacement detecting device for switching the first and second light sources.

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