JP5861546B2 - Object movement control device and Fourier transform infrared spectrophotometer - Google Patents

Description

  The present invention relates to a movement control device for an object that moves on a straight line along a linear guide, and a Fourier transform infrared spectrophotometer (hereinafter referred to as FTIR) as an example of a device including the movement control device. It is.

  FTIR is used for qualitative analysis and quantitative analysis of substances, and can be used for a wide range of substances regardless of organic substances and inorganic substances. In FTTR, analysis is performed by reciprocating the moving mirror to acquire an interference signal. However, since the detector has frequency characteristics, it is important that the moving mirror moves at a constant speed when collecting data. In order to obtain a constant speed, feedback control is performed to acquire the current speed and correct an error from the target speed. A laser interferometer is used to obtain the current speed. When the position of the moving mirror changes, the intensity of the laser interference signal changes. When the moving mirror moves at a constant speed, the laser interference signal is detected as a sine wave having a constant frequency. If this interference signal is treated as a signal with positive and negative amplitudes (called a fringe signal) from the ground level, the time from the rising zero cross (when rising from the ground level) to the next rising zero cross is measured. Thus, the time when the movable mirror moves by the distance of the optical path difference corresponding to one wavelength of the laser can be measured. That is, the speed of the movable mirror can be measured.

  The present inventor has a moving mirror control device including a control interferometer that is a system in which the moving mirror is suspended so that its initial balance position is in the direction of gravity. Based on the values obtained by multiplying each of the distance from the balance position of the moving mirror, the current speed of the moving mirror, and the difference between the current speed of the moving mirror and the target speed by using the measured value of the speed, the moving mirror FTIR that feedback-controls the current applied to drive the movable mirror so that the moving speed of the moving mirror becomes the target speed is proposed (see Patent Document 1). As a variable parameter, the variable parameter is adjusted to an optimum value so that the moving speed of the movable mirror becomes the target speed at the time of adjustment.

  The present invention picks up an object that moves on a straight line along a linear guide, instead of such a moving mirror. The object may be a moving mirror itself, but may be another object. In the case of other objects, a movable mirror is attached as a unit. In a moving mirror that moves on a straight line along the linear guide, a voltage is applied to the coil that drives the movement of the moving mirror, and the moving mirror moves on the linear guide by the electromagnetic force generated by the current flowing through the coil and the magnetic field generated by the magnet. Therefore, the speed of the movable mirror is controlled by sequentially changing the voltage applied to the coil that drives the movement of the movable mirror.

JP 2009-139352 A

  The optimum value of the control parameter such as the proportional coefficient varies depending on the state of the apparatus due to various causes such as poor quality of the linear guide or aging deterioration. If the control parameter is not an appropriate value, there may be a situation where the performance of the apparatus is not sufficient or an error occurs during measurement. Therefore, in order to draw out the performance of the apparatus, it is necessary to keep the control parameter at an appropriate value, but it takes time to determine the control parameter.

  An object of the present invention is to enable automatic determination of control parameters.

  In the present invention, feedback control by PID control is performed in order to control the movement of the object that moves on a straight line along the linear guide. PID control is a feedback control method in which an input value is controlled by three elements: a deviation between an output value and a target value, its integration, and differentiation. In PID control, the voltage applied to the drive coil is determined using the following PID control equation.

V _n = C _P V _err + C _{D ΔV} + C _I ΣV _err + C _F (1)
here,
V _n : a desired voltage (voltage to be applied this time),
V _err : Speed error,
Δ _V : Difference between the previous speed and current speed,
ΣV _err : Sum of speed errors,
C _P : proportional coefficient,
C _D : differential coefficient,
C _I : integration coefficient,
C _F : Coefficient of friction.

Proportional coefficient C _P , differential coefficient C _D , integral coefficient C _I and friction coefficient C _F are called control parameters, C _P V _err is a proportional term, C _{D ΔV} is a differential term, C _I ΣV _err is an integral term, C _F is called the friction term. The control parameter is conventionally determined experimentally or empirically, but is automatically determined in the present invention.

In the linear guide, a part with a movable range is slippery, and a part adjacent to the part is slippery. This is a point different from the suspension type moving mechanism previously proposed by the present inventor in Patent Document 1. In the linear guide, a high voltage is applied to control a part with poor slip, but when the part enters a part with good slip in that state, the speed of the movable mirror increases rapidly. At that time, voltage is applied in the direction to suppress the speed (reverse direction), but if the voltage in the direction to suppress is too large, the moving mirror stops, and the moving mirror is moved again until the speed error becomes small It will take time. Therefore, the applied voltage in the reverse direction must not be applied beyond a certain level. On the other hand, even if the applied voltage in the reverse direction is too small, a portion where the speed error is large continues after the speed is increased, so that a voltage higher than a certain level is required. The maximum voltage V _A of the reverse direction applied voltage is also an important amount. Therefore, the reverse maximum voltage V _A is also treated as a control parameter in the present invention.

  In the present invention, a CPU used for interferometer control is used, and a function for changing control parameters and a function for acquiring a speed error are provided in a program executed by the CPU. Using this function, the speed error is small, and the control parameters are automatically determined so that the measurement does not stop.

  The object movement control device of the present invention arranges a phase plate between a beam splitter and a fixed mirror or a moving mirror, separates and detects two polarization components from an interference signal combined by the beam splitter, and detects each other. There is provided an interferometer that detects the moving direction and position of the movable mirror from the phase relationship and wave number of both detection signals that are out of phase. The movable mirror is driven by an electromagnetic force generated by a current flowing by a voltage applied to the coil, and is supported so as to move in a reciprocating direction on a straight line along the linear guide.

  A control unit is provided for controlling the voltage applied to the coil to drive the movable mirror. The control unit includes an interferometer driving unit, a control parameter holding unit, and a parameter adjusting unit.

The interferometer drive unit uses a measured value of the current position and current speed of the movable mirror to determine a voltage to be applied to drive the movable mirror so that the moving speed of the movable mirror becomes a set target speed. Proportional coefficient C _P , differential coefficient C _D , integral coefficient C _I , friction coefficient C _F , and reverse maximum voltage V _A that is the maximum value of the reverse voltage applied in the direction to suppress the moving mirror speed during feedback control. As a control parameter, feedback control is performed by the PID method over the set operation range of the linear guide.

  The control parameter holding unit holds control parameters used in the interferometer driving unit.

The parameter adjustment unit performs feedback control on at least one of the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _{I, the} friction coefficient C _F , and the reverse maximum voltage V _A to measure the current speed measurement value and the target The optimum value of the control parameter is determined by an evaluation function based on the error from the speed. The determined control parameter is held in the control parameter holding unit, and when the control parameter is already held, it is updated with the determined new control parameter.

  Here, the control unit uses the expression “controls the voltage applied to the coil”. However, since the voltage is applied to the coil in order to pass a current through the coil, It is the same as “control”. Therefore, the present invention includes a device that performs PID control on the current flowing through the coil.

  In a preferred embodiment, the interferometer driver can change the target speed. In that case, when the target speed is changed, the parameter adjustment unit obtains a new optimum value of the control parameter, and updates the control parameter held in the control parameter holding unit.

  In another preferred embodiment, the interferometer driver can change the operating range. In that case, when the operating range is changed, the parameter adjustment unit obtains a new optimum value of the control parameter and updates the control parameter held in the control parameter holding unit.

  An example of an apparatus using such an object movement control apparatus is FTIR. In FTIR, a phase plate is placed between the beam splitter of the main interferometer that measures the sample and the fixed or moving mirror, and the two polarization components are separated from the interference signal combined by the beam splitter and detected. And a moving mirror control device equipped with a control interferometer that detects the moving direction and position of the moving mirror from the phase relationship and wave number of both detection signals that are out of phase with each other. The object movement control device of the present invention is used as the device.

  In the object movement control device of the present invention, since the control parameter can be automatically determined, it is possible to reduce the influence on the performance due to individual differences and aging of the object movement control device and its components. In addition, since it is not necessary for an engineer with knowledge to adjust control parameters to make adjustments, it is possible to make adjustments at any time, not only during production, but also during installation and movement of the equipment, thereby drawing out the performance of the equipment. This makes it easier to reduce the adjustment man-hours.

  The same effect can be achieved for FTIR using the object movement control device as a moving mirror control device.

It is a block diagram which shows the structure of an example of FTIR to which this invention is applied. It is a block diagram which shows the movable mirror control mechanism in the same FTIR. It is a block diagram which shows the structure of the control part in the same FTIR. It is a block diagram which shows the function of the control part. It is a flowchart which shows operation | movement of one Example.

  FIG. 1 shows an example of FTIR to which the present invention is applied. The beam splitter and compensator (simply referred to as a beam splitter) 2 includes an interferometer composed of a fixed mirror 4 and a moving mirror 6, and the beam splitter 2 has a normal direction of the fixed mirror 4 and a normal direction of the moving mirror 6. Are arranged with an inclination of 30 degrees. The fixed mirror 4 is mounted on a fixed mirror support block 8, the moving mirror 6 is supported by a sliding mechanism 14, and the sliding mechanism 14 is reciprocated in a direction in which the moving mirror 6 is moved toward and away from the beam splitter 2 by a linear motor 16. Move to. A current is supplied to the linear motor 16 from the power amplifier 18, and the current supplied to the linear motor 16 is controlled from the sliding controller 20 via the power amplifier 18.

  In order to configure the main interferometer together with the beam splitter 2, the fixed mirror 4, and the movable mirror 6 to form an infrared spectroscopic measurement system, an infrared light source 22 is provided, and infrared rays from the light source 22 are collected by a condensing mirror 24 and an aperture 26. Then, the light enters the beam splitter 2 through the collimator mirror 28 and is modulated by the interferometer. The modulated light passes through the sample chamber 34 from the mirror 30 and the condensing mirror 32, and then is received by the infrared detector 38 through the ellipsoidal mirror 36 and converted into an electrical signal. A preamplifier 40 is provided for amplifying the detection signal of the detector 38. The detection signal amplified by the preamplifier 40 is sampled by a sample hold amplifier 46 through a filter 42 and an auto gain amplifier 44, and is converted into a digital signal by an AD converter 48. And is sent to the CPU bus line 84.

  In order to constitute a control interferometer together with the beam splitter 2, the fixed mirror 4 and the movable mirror 6, a He—Ne laser 50 is provided as a light source. The laser beam from the laser 50 is incident on the beam splitter 2 by the half mirror 54. In order to change the laser beam reflected by the beam splitter 2, reflected by the fixed mirror 4, and returned to the beam splitter 2 again from linearly polarized light to circularly polarized light, a (λ / 8) plate 56 is provided between the beam splitter 2 and the fixed mirror 4. Is provided. The (λ / 8 plate) 56 is installed such that its polarization axis is inclined 45 degrees from the polarization plane of the incident laser beam.

  A polarization beam splitter 60 is provided to divide the interference light modulated by the interferometer and reflected by the half mirror 58 into P-wave and S-wave polarization components. A photodiode 62 is provided as a detector that receives one polarization component transmitted through the polarization beam splitter 60, and a photodiode 64 is provided as a detector that receives the other polarization component reflected by the polarization beam splitter 60. . A signal detected by the photodiodes 62 and 64 is a fringe signal. The photodiode 62 is connected to the preamplifier 66, and the photodiode 64 is connected to the preamplifier 68. Detection signals of the respective polarization components amplified by the preamplifiers 66 and 68 are converted into pulse train signals a and b by waveform shapers 78 and 80, respectively. The two waveform shaped pulse signals a and b are input to the up / down counter 82. The up / down counter 82 determines the up / down mode from the phase relationship between the two input signals, counts the number of pulses of the input signal, and sends it to the CPU bus line 84.

  The pulse signal a generated by shaping the detection signal of the photodiode 62 is also sent to the sliding controller 20, the sample hold amplifier 46, and the AD converter 48. The CPU bus line 84 includes a control unit 86, a program storage memory 88, a data storage memory 90, an external storage device 92, an LCD (liquid crystal display) 94, a plotter 96, an auto gain amplifier 44, an AD converter 48, and an up / down counter. 82 is connected.

  FIG. 2 shows a movable mirror control mechanism in the same embodiment. The movable mirror 6 is attached to a voice coil 17, and the voice coil 17 is combined with a magnet 19. Since the voice coil 17 is supported so as to move in a reciprocating direction along a straight line along the linear guide 15, the movable mirror 6 moves along the linear guide 15 as the voice coil 17 moves. The movable mirror 6 is driven and moved by an electromagnetic force generated by a current flowing by a voltage applied to the voice coil 17.

  Since the control system for controlling the movement of the movable mirror 6 is shown in detail in FIG. 1, it is schematically shown in a block diagram in FIG. The beam splitter 2, the fixed mirror 4, the movable mirror 6, and the laser light source 50 that constitute the control interferometer, the fringe signal generation units 60, 62, 64, and 82, the CPU 86 that is the control unit, and the sliding controller 20 are represented. A DA converter 20 is schematically shown.

  As shown in FIG. 3, the controller 86 includes an interferometer control CPU 100, a data processing CPU 102, and an EEPROM (electrically erasable PROM) 88a for storing control parameters used to calculate driving voltage values for the movable mirror 6. Is included. An external PC (personal computer) 104 is connected to the control unit 86.

FIG. 4 shows the control unit 86 as a function. The interferometer driving unit corresponds to the interferometer driving CPU 100 and drives the moving mirror 6 so that the moving speed of the moving mirror 6 becomes the set target speed using the current position of the moving mirror 6 and the measured value of the current speed. The operating range of the linear guide 15 is set with the voltage to be applied to the PID control equation using the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _I , the friction coefficient C _F , and the reverse maximum voltage V _A as control parameters. The feedback control is performed by the PID method. The control parameter holding unit is realized by the EEPROM 88a and holds control parameters used in the interferometer driving unit. The parameter adjustment unit 106 is realized by the data processing CPU 102 and performs feedback control on at least one of the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _I, and the friction coefficient C _{F and} the reverse maximum voltage V _A. A control parameter is determined by obtaining an optimum value by an evaluation function based on an error between the measured value of the current speed and the target speed. The determined control parameter is held in the control parameter holding unit, or when the control parameter is already held in the control parameter holding unit, the held control parameter is updated with the newly determined control parameter. The

The operation of this FTIR will be described.
(A) Operation of the control interferometer:
The laser interference light beams having different phases separated by the polarization beam splitter 60 are received by the photodiodes 62 and 64, respectively, and the detection signals of the respective photodiodes 62 and 64 are waveform-shaped to be pulse signals. It is taken in as two input signals a and b of the counter 82. The up / down counter 82 obtains the up / down mode from the phase relationship between both input signals. That is, if the moving mirror 6 is in the direction approaching the beam splitter 2, the signal a is advanced in phase by 90 degrees with respect to the other signal b. This is because the phase of a is delayed by 90 degrees with respect to b. The number of pulses of the input signal counted by the up / down counter 82 is a signal depending on the position of the movable mirror 6. The output signal of the up / down counter 82 is taken into the interferometer control CPU 100 of the control unit 86 via the bus line 84 to detect an abnormal sliding of the moving mirror and to integrate the interferogram of the infrared spectroscopic measurement. It is used as a signal when performing

  The sliding controller 20 controls the voltage applied to the linear motor 16 via the power amplifier 18 so that the frequency of the detection signal of the photodiode 62 becomes constant. A signal obtained by shaping the detection output of the photodiode 62 (a signal) is also used as a sampling signal of the sample hold amplifier 46 and a conversion start signal of the A / D converter 48.

(B) Infrared data collection operation:
A signal emitted from the infrared light source 22, modulated by an interferometer, converted into an electrical signal by the infrared detector 38 through the sample chamber 34, the filter 42, the auto gain amplifier 44, the sample hold amplifier 46. The A / D converter 48 converts the signal into a digital signal and takes it in the bus line 84. An interferogram is generated as the movable mirror 6 moves. A / D conversion of the A / D converter 48 is activated using the signal a which is an interference signal of the control interferometer. The current position of the movable mirror 6 is detected in real time by the quadrature control, and this current position signal is generated by the up / down counter 82 in order to know the data collection start and end points of a series of interferograms. In succession, the interferometer control CPU 100 of the control unit 86 recognizes and collects data in the reciprocating direction of the movable mirror 6.

FIG. 5 is a flowchart showing the operation of the embodiment.
(1) The initial value of the control parameter is set (step S1). There are five control parameters: proportional coefficient C _P , differential coefficient C _D , integral coefficient C _I , friction coefficient C _F, and reverse maximum voltage V _A. Initial values are set for all these five control parameters. The initial value of the control parameter may be a value experimentally determined using some devices. The adjustment time can be shortened by starting from the initial value.

(2) A search range for changing the control parameter is set (step S2). There are several methods for setting the search range. Two examples of setting methods are given.

a) A method of searching only within a certain range from the initial value. If this method is adopted, the optimum place may not be found, but the adjustment time can be shortened. In this case, there are a method for searching only within a certain range for all five control parameters, and a method for searching only within a certain range only for control parameters selected by limiting the number of control parameters to be searched. In the latter case, the search is limited to 1 to 3 types among the proportionality coefficient C _P , the differential coefficient C _D , the integral coefficient C _I, and the friction coefficient C _F and the reverse maximum voltage V _A. In order to make it simpler, the search may be limited to one of the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _I and the friction coefficient C _F and the reverse maximum voltage V _A.

  b) A method for searching a wide range. This method increases the possibility of finding the optimum place instead of taking adjustment time. With regard to the types of control parameters to be searched for in this method as well, what has been described in a) above applies.

(3) The operation of the movable mirror is started (step S3).

(4) The speed error is measured (step S4). Since the speed error can be measured at each fringe, the speed error V _err for each fringe is stored. Here, depending on the values set for the search for the control parameters to be searched, the movable mirror may not be controlled correctly and may stop. In the case of stopping, it is determined that the acquisition of the speed error is not completed within the specified time, and the set control parameter value is excluded from the evaluation target.

(5) When the movement of the movable mirror over a predetermined range is completed (step S5), an evaluation function is calculated (step S6). An example of the evaluation function f (C _P , C _D , C _I , C _F , V _A ) is shown below.
f (C _P , C _D , C _I , C _F , V _A ) = α | _Verr | _ave + β | _Verr | _max
Here, α and β are weighting factors, | V _err | _ave is an average value of the absolute values of the speed error V _err , and | V _err | _max is a maximum value of the absolute value of the speed error V _err .

  Furthermore, since a situation where the speed error changes suddenly should be avoided, if there is a part where the speed error exceeds a specified value, an evaluation function value is given by increasing the value of the evaluation function.

The above evaluation function is an example, and other evaluation functions can be used. For example, the average value of the absolute value of the speed error V _err is used instead of the average value of the absolute value of the speed error, or the maximum value of the absolute value of the speed error V _err is used _instead of the maximum value of the absolute value of the speed error. The difference between the value and the minimum value can also be used.

(6) When the search of the search range for the control parameter to be searched is completed (step S7), the optimum control parameter is extracted from the evaluation function values calculated so far and set as a new control parameter (step S8). When the evaluation function as described above is selected, a control parameter that minimizes the value may be selected as the optimum value.

(7) If the search is not completed (step S9), a new control parameter to be searched is set, and steps 3 to 6 are repeated. The following method can be considered as a new parameter setting method.

(A) The control parameter is increased or decreased by an arbitrary width.

(B) The control parameter increase / decrease direction and increase / decrease value are determined based on the evaluation function calculation results obtained so far. In this case, the number of searches and the convergence condition may be given as the search end condition. As the convergence condition, for example, the value of the evaluation function when the control parameter is increased or decreased can be included in a predetermined range.

  The above is the flow of the present invention, and the obtained control parameters are stored in the control parameter holding unit 88a composed of the EEPROM in the FTIR. The control parameter holding unit may be provided in an external computer connected to the FTIR, such as a personal computer (PC).

  Since the control parameters vary depending on the operating speed of the moving mirror, if the FTIR can change the operating speed of the moving mirror, when the operating speed is changed, a search is performed for that operating speed. An optimum control parameter is obtained, and the control parameter stored in the control parameter holding unit 88a is updated.

  The optimal value of the control parameter may change depending on the operating range of the movable mirror. For example, if the processing accuracy is poor at the end of the linear guide, it is conceivable that the appropriate control parameters differ depending on whether only the center is used or when the end is used up to the end. Therefore, when the FTIR can change the operating range of the movable mirror, when the operating range is changed, a search is performed on the operating range to obtain an optimal control parameter and the control parameter is retained. The control parameter stored in the unit 88a is updated.

  In the embodiment, the case where the object is the FTIR moving mirror itself has been described, but the present invention can also be applied to another object even if the object is not the moving mirror itself. In that case, the movable mirror is integrally attached to the object. Therefore, the present invention can be applied to a wide range of fields in which it is required to control an object to move along a linear guide on a straight line at a constant speed.

2 Beam splitter 4 Fixed mirror 6 Moving mirror 15 Linear guide 16 Linear motor 86 Control unit 88a Control parameter holding unit 100 Interferometer control unit 106 Parameter adjustment unit

Claims (4)

A phase plate is arranged between the beam splitter and the fixed or moving mirror, and the two polarization components are separated and detected from the interference signal combined by the beam splitter, and the two detection signals that are out of phase with each other are detected. In the object movement control device equipped with an interferometer of a method for detecting the moving direction and position of the moving mirror from the phase relationship and wave number,
The movable mirror is driven by an electromagnetic force generated by a current flowing by a voltage applied to a coil, and is supported so as to move in a reciprocating direction on a straight line along a linear guide.
The controller that controls the voltage applied to the coil to drive the moving mirror uses the current position of the moving mirror and the measured value of the current speed so that the moving speed of the moving mirror becomes a set target speed. The voltage applied to drive the movable mirror is proportional to the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _I , the friction coefficient C _F of the PID control equation, and the direction in which the speed of the movable mirror is suppressed during feedback control. An interferometer driver that performs feedback control in a PID manner over the set operating range of the linear guide, with a reverse maximum voltage that is the maximum value of the reverse voltage applied as a control parameter;
A control parameter holding unit for holding control parameters used in the interferometer driving unit;
At least one of the proportional coefficient C _P , the differential coefficient C _D , the integral coefficient C _{I, the} friction coefficient C _{F and} the reverse maximum voltage is evaluated based on an error between the measured value of the current speed and the target speed by performing feedback control. A parameter adjustment unit that determines the optimum value of the control parameter by a function;
An object movement control device comprising:   The interferometer drive unit can change the target speed, and the parameter adjustment unit obtains a new optimum value of the control parameter when the target speed is changed, and is held in the control parameter holding unit. The object movement control device according to claim 1, wherein the control parameter is updated.   The interferometer drive unit can change the operation range, and the parameter adjustment unit obtains a new optimum value of the control parameter when the operation range is changed, and is held in the control parameter holding unit. The object movement control device according to claim 1 or 2, wherein the control parameter is updated. A phase plate is arranged between the beam splitter of the main interferometer for measuring the sample and the fixed mirror or moving mirror, and the two polarization components are separated and detected from the interference signal combined by the beam splitter. In a Fourier transform infrared spectrophotometer equipped with a moving mirror control device equipped with a control interferometer that detects the moving direction and position of the moving mirror from the phase relationship and wave number of both detection signals that are out of phase ,
The Fourier transform infrared spectrophotometer, wherein the moving mirror control device is the object movement control device according to any one of claims 1 to 3.

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