JP2006296136A - Linear motor control system and stirling refrigeration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a linear motor control system capable of precisely calculating the stroke of a moving member, and preventing collision with other parts in the moving member, and to provide a stirling refrigeration system using the linear motor control system. <P>SOLUTION: A microcomputer assumes that each of a motor voltage v(t), a motor current i(t), and an induction voltage generated in the linear motor is a sinusoidal wave having the same angular velocity ω, and uses a voltage signal for indicating the motor voltage v(t) of the linear motor and a current signal for indicating the motor current i(t) for calculating the effective value E of the induction voltage in one cycle of the sinusoidal wave. After that, the effective value E of the induction voltage, the angular velocity ω, and an induction voltage coefficient (thrust coefficient) α are used for calculating a stroke ST of the moving member in one cycle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a linear motor control system that controls a linear motor and a Stirling refrigeration system using the linear motor control system.

Conventionally, a system for applying an AC voltage to drive a linear motor has been used. This system calculates the stroke of a piston using a back electromotive force, that is, an induced voltage generated in a linear motor without using a displacement sensor.
JP-A-9-126147 JP 2003-339188 A JP 2003-314919 A JP 2003-65244 A

  The conventional linear motor control system employs a method of calculating the stroke of the mover based on the induced voltage generated in the linear motor.

  For example, in the system disclosed in Japanese Patent Laid-Open No. 9-126147, first, the instantaneous value of the induced voltage is calculated using the differential value of the current of the linear motor. Next, the instantaneous value of the speed of the mover is calculated using the instantaneous value of the induced voltage. Thereafter, the instantaneous value of the velocity of the mover is integrated for one period. Finally, the stroke of the mover is calculated using the difference value between the maximum value and the minimum value of the integral values. According to this method, there is a problem that stroke calculation errors in calculation processing of the differentiation circuit and integration circuit or the microcomputer increase, and the cost required for these control devices increases.

  Further, in the system disclosed in Japanese Patent Laid-Open No. 2003-339188, a method is used in which the stroke of the mover is estimated from the instantaneous value of the mover speed at the peak of the motor current. If the phase of the induced voltage is not constant, or if the phase of the motor current and the phase of the induced voltage do not match, the calculation error of the stroke of the mover becomes large.

  Furthermore, since the system disclosed in Japanese Patent Application Laid-Open No. 2003-314919 does not perform calculation according to the vector method of alternating current amount, there is a problem that the stroke cannot be calculated with high accuracy.

  In the method disclosed in Japanese Patent Laid-Open No. 2003-65244, the stroke is calculated using the instantaneous value (maximum value) of the induced voltage. However, according to this method, since the instantaneous value of the induced voltage varies greatly due to noise or the like, a stroke calculation error increases.

  Further, when the load generated in the linear motor increases, the thrust coefficient inherent to the linear motor, that is, the induced voltage coefficient, decreases due to the influence of magnetic saturation. Therefore, according to the method of calculating the stroke of the mover using a constant induced voltage coefficient, there is also a problem that the accuracy of the calculation result of the mover stroke is reduced as the load of the linear motor is increased.

  Due to the above problems, in the conventional linear motor control system, since the calculation accuracy of the stroke value of the mover is low, the stroke of the mover cannot be controlled with high accuracy. Therefore, the malfunction that a needle | mover will operate | move with a stroke larger than a limit stroke and will collide with another site | part will arise.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a linear motor control system capable of accurately performing the stroke control of the mover by calculating the actual stroke of the mover with high accuracy. And providing a Stirling refrigeration system in which it is used.

  A linear motor control system according to one aspect of the present invention includes a linear motor in which a mover reciprocates, voltage detection means for detecting a motor voltage applied to the linear motor, and a motor current flowing in the linear motor. And a microcomputer for receiving a voltage signal capable of specifying the instantaneous value of the motor voltage and a current signal capable of specifying the instantaneous value of the motor current. Further, the microcomputer assumes that each of the motor voltage, the motor current, and the induced voltage (back electromotive force) generated by the reciprocating motion of the mover is a sine wave having the same angular velocity, and uses the voltage signal and the current signal. Using the means for calculating the effective value of the induced voltage in one cycle of the sine wave, the effective value of the induced voltage, the angular velocity of the voltage signal and the current signal, and the induced voltage coefficient (thrust coefficient), the mover in one cycle Means for calculating the stroke.

  According to the above configuration, since the stroke of the mover can be calculated with high accuracy using the effective value of the induced voltage, the stroke of the mover can be controlled more accurately.

  A linear motor control system according to another aspect of the present invention includes a linear motor in which a mover reciprocates, voltage detection means for detecting a motor voltage applied to the linear motor, and a motor current flowing through the linear motor. And a microcomputer for receiving a voltage signal capable of specifying the instantaneous value of the motor voltage and a current signal capable of specifying the instantaneous value of the motor current. Further, the microcomputer uses the voltage signal and the current signal to calculate the phase difference θ between the motor voltage and the motor current and the angular velocity ω of the voltage signal and the current signal, the motor voltage, the motor current, and the movable Assuming that each induced voltage (back electromotive force) generated by the reciprocating motion of the child is a sine wave having the same angular velocity ω, the effective value of the motor voltage in one cycle of the sine wave using the voltage signal and the current signal Means for calculating V and effective value I of motor current, effective value V of motor voltage, effective value I of motor current, phase difference θ, winding resistance value R of linear motor, and inductance L value of linear motor Means for substituting in (1) and calculating the effective value E of the induced voltage;

  Means for substituting the effective value E of the induced voltage E, the angular velocity ω, and the induced voltage coefficient (thrust coefficient) α into the following equation (2) to calculate the stroke ST of the mover in the above-mentioned one cycle;

  Have

  A linear motor control system according to one aspect or another aspect of the present invention includes a DC power source, an inverter circuit that is electrically connected between the DC power source and the linear motor, and drives the linear motor, and a DC power source and an inverter circuit. And a microcomputer connected to each other, and the microcomputer detects an instantaneous value corresponding to one period of the potential difference between both ends of the resistor, whereby a maximum value and a minimum value within one period of the motor current are detected. It is desirable to calculate the value and calculate the effective value I of the motor current using the maximum value and the minimum value.

  According to the above configuration, since the pulse width of PWM (Pulse Width Modulation) at the timing near the zero cross point of the motor voltage is small, the instantaneous value of the motor current at that timing cannot be detected. In addition, the effective value of the motor current can be accurately estimated.

  A linear motor control system according to still another aspect of the present invention includes a linear motor in which a mover reciprocates, voltage detection means for detecting a motor voltage applied to the linear motor, and a motor current flowing through the linear motor. Current detection means for detecting, and a microcomputer for receiving a voltage signal capable of specifying the instantaneous value of the motor voltage and a current signal capable of specifying the instantaneous value of the motor current are provided. Further, the microcomputer uses the voltage signal and the current signal to calculate the effective value of the angular velocity, the induced voltage (back electromotive force) generated by the reciprocating motion of the mover, and the total number of magnetic fluxes generated in the magnetic circuit of the linear motor. Means, an approximate expression or data table for specifying the relationship between the effective value of the total magnetic flux number and the induced voltage coefficient (thrust coefficient), and the effective value of the total magnetic flux number and the approximate expression or data table. And means for calculating the stroke of the mover using the induced voltage, the angular velocity, and the corrected induced voltage coefficient.

  According to said structure, since an induced voltage coefficient is correct | amended according to the load of a linear motor, the stroke of a needle | mover can be calculated more correctly.

  The Stirling refrigeration system of the present invention includes the linear motor control system according to the above-described one aspect, another aspect, or still another aspect, and the displacer that reciprocates according to the reciprocating movement of the piston as the above-described mover. .

  According to said structure, since the stroke of a piston is detected correctly, the collision with a piston and a displacer can be prevented reliably.

  ADVANTAGE OF THE INVENTION According to this invention, the linear motor control system which can perform the stroke control of a needle | mover accurately by calculating the actual stroke of a needle | mover with high precision, and the Stirling refrigeration system using the same are obtained.

  Hereinafter, a linear motor control system according to an embodiment of the present invention will be described with reference to the drawings.

  In the linear motor control system of the present embodiment, in order to solve the problem of the method of calculating the stroke of the linear motor movable element using the instantaneous value of the induced voltage of the linear motor, the linear motor circuit variable (voltage And current etc.) are all regarded as sine waves, and the induced voltage generated in the linear motor is calculated in units of effective values for one cycle. According to this method, the stroke of the mover can be calculated with a simple process and with high accuracy. Hereinafter, the linear motor control system of the present embodiment will be specifically described.

  First, the configuration of the linear motor control system of the present invention will be described with reference to FIGS. FIG. 1 shows the configuration of the linear motor drive circuit. In FIG. 1, i (t) is a function indicating a motor current flowing through the linear motor, v (t) is a function indicating a motor voltage applied to the linear motor, and e (t) is a reciprocating motion of the mover. Is a function indicating the induced voltage (counterelectromotive force) generated by, R is a constant indicating the winding resistance value of the linear motor, and L is a constant indicating the inductance of the linear motor. Note that t is a variable indicating time.

  When the circuit shown in FIG. 1 is represented by a general equation, the following equation (3) is obtained.

  Further, the induced voltage e (t) is expressed as a function of the induced voltage coefficient α (thrust coefficient) depending on the magnetic characteristics and drive circuit of the linear motor and the velocity vp (t) of the mover (piston). become that way.

  FIG. 2 shows a motor current i (t), a motor voltage v (t), and an induced voltage e (t when a sinusoidal motor voltage V (t) having an effective value V and an angular velocity ω is applied to the linear motor. ) Shows a change in one cycle of each instantaneous value.

  As shown in FIG. 2, it is assumed that the mover of the linear motor has a motion represented by an ideal sine wave, that is, a simple vibration, and has the same angular velocity as the angular velocity ω of the motor voltage v (t). If the value of the induced voltage coefficient α is constant regardless of the position of the mover, the current i (t) is also an ideal sine wave, and the angular velocity ω of the motor voltage v (t) Have the same angular velocity.

  If the effective value of the motor current is I, the effective value of the motor voltage is V, and the effective value of the induced voltage is E, the motor current i (t), the motor voltage v (t), The instantaneous values of the induced voltage e (t) are expressed by the following equations (5) to (7) with the phase of the current i (t) as a reference.

  In Equation (6), θ is a phase difference between the motor current i (t) and the motor voltage v (t).

In Equation (7), θ ₂ is a phase difference between the motor current i (t) and the induced voltage e (t).

  Further, the term of the induction voltage L · di (t) / dt of the coil in the equation (3) is expressed by the following equation (8).

The above-described matters are illustrated in FIG. 3 according to the vector notation method of the AC amount.
Therefore, if the effective value V of the motor voltage, the angular velocity ω, the effective value I of the motor current, and the phase difference θ can be obtained, the effective value E of the induced voltage E, using the following equations (9) and (10): And the phase difference θ ₂ can be calculated.

  The effective value I of the motor current and the effective value V of the motor voltage are expressed by the following equations (11) and (12).

  In equation (11), each of i (1), i (2),... I (n-1), i (n) is an instantaneous value of the motor current i (t). n is a natural number. Further, the sampling period of the instantaneous value of the motor current i (t) coincides with the PWM carrier period.

  In equation (12), each of v (1), v (2),... V (n−1), v (n) is an instantaneous value of the motor voltage v (t). n is a natural number. The sampling period of the instantaneous value of the motor voltage v (t) is coincident with the PWM carrier period.

  The speed vp (t) of the mover of the linear motor can be summarized by substituting Equation (7) into Equation (4).

  It becomes.

  When both sides of the equation (13) are integrated over time, the position Xp of the mover is expressed by the following equation (14).

  In Expression (14), Xp0 is a value of the neutral position in one cycle of the mover, that is, a value of the center position of the stroke.

  Therefore, the distance Xpmax between the neutral position Xp0 and the position farthest from the neutral position Xp0 is expressed by the following equation (15).

  Since the distance Xpmax corresponds to the amplitude of the mover, the stroke ST of the mover is a value twice the distance Xpmax, that is, 2Xpmax.

  From the above, if the respective values of the effective value V of the motor voltage, the angular velocity ω, the effective value I of the motor current, and the phase difference θ between the motor current i (t) and the motor voltage v (t) are obtained, the above calculation is performed. The stroke ST of the linear motor can be accurately calculated using the equation.

  Next, a method for acquiring each variable of the linear motor driving circuit described above will be described.

  Since the angular velocity ω of the motor voltage v (t) and the motor current i (t) corresponds to a control command transmitted from the microcomputer to the inverter circuit, the microcomputer can always grasp the angular velocity ω. is there.

  The effective value I of the motor current and the effective value V of the motor voltage are detected as follows. First, instantaneous values of the motor voltage v (t) and the motor current i (t) are measured at a predetermined sampling period by using an AD (Analog to Digital) conversion function of the microcomputer. Next, the square root of the mean square value of all instantaneous values of the motor current i (t) in one cycle, that is, the effective value I of the motor current is calculated using the above-described equation (11). Further, the square root of the mean square value of all instantaneous values of the motor voltage v (t) in one cycle, that is, the effective value V of the motor voltage is calculated using the above-described equation (12). Note that, under the assumption that each of the motor current i (t) and the motor voltage v (t) is a sine wave, the maximum value and minimum value of the motor current i (t) for one cycle, and one cycle If the maximum value and the minimum value of the motor voltage v (t) are obtained and the effective value I of the motor current and the effective value V of the motor voltage are calculated using these values, the calculation becomes easier.

  In the detection of the phase difference θ described above, first, the motor current i (t) and the motor voltage v (t) are used by using the instantaneous values of the motor current i (t) and the motor voltage v (t). Figure out the phase of each zero cross point. Next, the phase difference between the zero cross points of the motor current i (t) and the motor voltage v (t) is calculated. This phase difference is defined as a phase difference θ between the motor current i (t) and the motor voltage v (t).

  Also in the linear motor of the above-described embodiment, the induced voltage coefficient α decreases due to the influence of the magnetic saturation as in the conventional linear motor. Therefore, in order to solve this problem, in the linear motor of the present embodiment, there is a process for correcting the induced voltage coefficient α using the magnetic strength (effective value Φ of the total number of magnetic fluxes in one cycle). Executed. As a result, the influence of magnetic saturation of the linear motor is removed, and a decrease in the accuracy of calculating the stroke of the mover is prevented.

  In order to perform the above-described correction when the linear motor is operating, the relationship between the magnetic strength (effective value Φ of the number of magnetic fluxes in one cycle) and the induced voltage coefficient α as shown in FIG. It is necessary to prepare an approximate expression or a data table indicating the correlation curve to be shown in advance.

  For this purpose, the induced voltage coefficient α and the effective value Φ of the total number of magnetic fluxes are set under appropriate linear motor operating conditions (the magnitude and frequency of the voltage applied to the linear motor and the load conditions) for creating the correlation curve. taking measurement.

  The method of measuring the induced voltage coefficient α is to measure the stroke ST of the mover with an external sensor (such as a laser displacement meter) under arbitrary operating conditions (the magnitude of the motor voltage, the angular velocity of the motor voltage, and the load condition) The effective value V of the motor voltage, the effective value I of the motor current, and the phase difference θ are measured by an external measuring instrument. The measured stroke ST (= 2Xpmax), the effective value V of the motor voltage, the effective value I of the motor current, and the phase difference θ, the winding resistance value R, the coil inductance L, The induced voltage coefficient α is calculated by substituting the angular velocity ω into the above equation (15).

  Next, how to obtain the effective value Φ of the total number of magnetic fluxes generated in the magnetic circuit of the linear motor drive circuit will be described.

The instantaneous value of the total number of magnetic fluxes φ (t) representing the magnetic strength in the magnetic circuit of the linear motor is equal to the instantaneous value of the number of magnetic fluxes φ _I (t) generated when a current flows through the coil, The sum of the number of magnetic fluxes φ _magnet (t) generated by the reciprocating motion and the instantaneous value is expressed by the following equation (16).

The instantaneous value of the number of magnetic fluxes φ _I (t) is expressed by the following equation (17).

  Substituting equation (5) into equation (17) yields the following equation (18).

The instantaneous value of the number of magnetic fluxes φ _magnet (t) is expressed by the following equation (19).

Assuming that the instantaneous offset value of the number of magnetic fluxes φ _magnet (t) is 0 and substituting equation (7) into equation (19), the following equation (20) is obtained.

Furthermore, the vector notation of the AC amount, effective value of the total number of magnetic fluxes [Phi, To illustrate the effective value [Phi _I and the effective value phi _magnet flux number becomes as shown in FIG.

  In addition, the vector diagram shown in FIG. 5 is drawn on the basis of the phase of the motor current, similarly to the vector diagram shown in FIG.

In FIG. 5, the effective value Φ of the total number of magnetic fluxes is a vector of the effective value Φ _{I of the} number of magnetic fluxes generated by the current flowing through the coil and the effective value Φ _{magnet of the} number of magnetic fluxes generated by the reciprocating motion of the mover magnet. Since it is the sum, the effective value Φ of the total number of magnetic fluxes in one cycle is obtained by the following equation (21).

  By the above calculation, data of the induced voltage coefficient α and the effective value Φ of the total number of magnetic fluxes under a certain condition can be obtained. In this way, when plotting data of a large number of induced voltage coefficients α and the effective value Φ of the total magnetic flux number under various conditions, the induced voltage coefficient α and the effective value Φ of the total magnetic flux number as shown in FIG. A correlation curve showing the relationship between

  If a data table or an approximate expression for specifying this correlation curve is stored in the memory inside the microcomputer, the effective value of the total number of magnetic fluxes can be obtained if the operating conditions of the linear motor are within a predetermined range. Using Φ, an induced voltage coefficient α suitable for the operating condition can be obtained. Therefore, according to the linear motor control system of the present embodiment, the stroke can be calculated with high accuracy by eliminating the adverse effect of magnetic saturation of the linear motor.

  The correction of the induced voltage coefficient α is not limited to the system that calculates the stroke ST using the effective value E of the induced voltage as described above, but also a system as disclosed in JP-A-2003-65244, That is, the present invention can also be used in a system that calculates a stroke using an instantaneous value (maximum value) of an induced voltage, an induced voltage coefficient, and an angular velocity.

  Specifically, the linear motor control system of the present embodiment described above includes a linear motor M having a reciprocating mover, an AC power source G and a smoothing circuit P that constitute a DC power source, as shown in FIG. The inverter circuit T that converts the DC power supplied from the above-mentioned DC power source into AC power and supplies the AC power to the linear motor M, and the microcomputer C that controls the inverter circuit T by PWM (Pulse Width Modulation) I have.

  Further, the linear motor control system includes a motor voltage detecting means U for detecting an instantaneous value of the motor voltage v (t) applied to the linear motor M, and a motor flowing through the linear motor M at a predetermined sampling period. Motor current detection means S for detecting an instantaneous current value i (t).

  The motor current detection means S in the present embodiment has a shunt resistor connected in series with the linear motor M between the inverter circuit T and the DC power supply, and an operational amplifier that amplifies the potential difference between both ends thereof. ing. The motor voltage detecting means U has resistors as voltage measuring voltage dividing means connected to both ends of the linear motor M. Further, the motor voltage detecting means U and the motor current detecting means S are respectively a voltage signal that can specify the instantaneous value of the motor voltage v (t) and a current signal that can specify the instantaneous value of the motor current i (t). Send to computer C.

  The microcomputer C includes a stroke command value output unit 101 that outputs a target stroke of the mover of the linear motor M, a stroke control unit 102 that receives stroke command value data, and a PWM signal transmitted from the stroke control unit 102. And a PWM control unit 103 that transmits a PWM pulse signal to the inverter circuit T based on the modulation rate command value.

  The stroke command value is determined according to the load condition, and is a value equal to or less than a limit value at which the mover collides with another part. The modulation rate command is a signal that can specify the PWM modulation rate. Further, the PWM control unit 103 outputs a pulse signal for controlling on / off of the switching elements constituting the inverter circuit based on the predetermined angular velocity ω and the modulation factor command value. As a result, a predetermined AC voltage is applied to the linear motor M.

  Further, the microcomputer C has a built-in AD (Analog to Digital) converter, and has a stroke calculation unit 104 that calculates the actual stroke ST of the mover based on the voltage signal and the current signal. The calculated actual stroke ST data is transmitted to the stroke control unit 102.

  The stroke control unit 102 performs control to bring the actual stroke closer to the target stroke command value by changing the PWM modulation rate according to the difference between the actual stroke ST and the target stroke command value. For example, when the actual stroke ST value is greater than or equal to a predetermined value, the stroke control unit 102 sets a modulation rate command value lower than the current modulation rate command value to reduce the stroke. Send to. Thereby, the PWM control unit 103 outputs each PWM pulse according to the given PWM modulation rate. As a result, the amplitude of the sinusoidal AC voltage applied to the linear motor M is reduced. Accordingly, the actual stroke ST of the mover of the linear motor M changes so as to approach the stroke command value. Further, by setting the stroke command value to a value lower than the limit value, it is possible to prevent the linear motor M from being damaged due to the piston colliding with another part.

  In addition, when the difference between the actual stroke ST and the target stroke command value is large, the stroke control unit 102 changes the PWM modulation rate according to the difference to target the actual stroke ST. Control to bring it closer to the stroke command value. Therefore, it is possible to increase the accuracy of control of the stroke of the mover.

  The motor voltage detection means U transmits a voltage signal that can specify the instantaneous value of the motor voltage v (t) of the linear motor M to the microcomputer C. The microcomputer C uses the AD conversion function to calculate the motor voltage v (t) applied to the linear motor M based on a signal that can identify the potential difference between both terminals of the linear motor M.

  The motor current detection means S detects the motor current i (t) flowing through the shunt resistor connected to the DC (Direct Current) line on the input side of the inverter. The motor current i (t) flows into the shunt resistor only during the ON period of the PWM pulse. Therefore, the motor current detection means S transmits a potential difference signal between both ends of the shunt resistor during the above-described ON period to the microcomputer C. The microcomputer C converts the potential difference signal into a current signal that can specify the motor current i (t) by the AD function. Therefore, it is desirable that the sampling period of the motor current i (t) coincides with the PWM carrier period.

  The stroke calculation unit 104 receives a voltage signal that can specify the instantaneous value of the motor voltage v (t) and a current signal that can specify the instantaneous value of the motor current i (t), and receives a motor signal for each cycle of the sine wave. The effective value V of the voltage, the effective value I of the motor current, and the phase difference θ are calculated.

  As described above, the effective value V of the motor voltage and the effective value I of the motor current are calculated as follows. The square root of the root mean square value of the total instantaneous values of the motor voltage v (t) in one cycle is a predetermined sampling cycle. And the method using the square root of the root mean square of all instantaneous values of motor current i (t) in one cycle, or the assumption that each of motor voltage v (t) and motor current i (t) is a sine wave Below, there is a method using the maximum value and the minimum value of the motor voltage v (t) and the motor current i (t), respectively.

  In the present embodiment, since the instantaneous value of the motor current i (t) is calculated using the potential difference between both ends of the shunt resistor of the motor current detecting means S, when the PWM pulse ON period is short, that is, At the timing close to the zero cross point of the motor voltage v (t), it is difficult to detect the instantaneous value of the motor current i (t). Therefore, under the assumption that the motor current i (t) is a sine wave, the maximum value and the minimum value during one cycle of the motor current i (t) and the waveform of the motor current stored in advance can be specified. It is desirable to use a method of estimating the total instantaneous value of the motor current i (t) during one cycle using data. In this method, the effective value I of the motor current is calculated using the following calculation formula.

  First, in the memory of the microcomputer C, first, as shown in FIG. 7, one cycle of the motor current i (t) calculated using the potential difference signals at both ends of the shunt resistor of the motor current detection means S is stored. A data string of all instantaneous values is stored. Next, the microcomputer C extracts the maximum value Imax and the minimum value Imin of the instantaneous value of the motor current i (t) from the data string, and the maximum value Imax and the minimum value Imin are expressed in the following equation (22). Substituting and calculating the effective value I of the motor current.

  According to the method as described above, the effective value I of the motor current can be accurately calculated even when the instantaneous value of the motor current i (t) at a timing close to the zero cross point of the voltage cannot be accurately detected.

  The phase difference θ between the motor voltage and the motor current is detected by the phase difference between the zero cross point of the motor current i (t) waveform and the zero cross point of the motor voltage v (t) waveform. However, in the current detection method using the shunt resistor described above, when the phase difference θ is small, that is, when the motor voltage zero cross point and the motor current zero cross point are close, the PWM pulse width is small and the motor current It is difficult to detect the zero cross point. In this case, it is desirable to use a method for estimating the phase of the zero cross point of the motor current based on the phase when the motor current becomes the maximum value in one cycle and the phase when the motor current becomes the minimum value.

  Effective value V of motor voltage, effective value I and phase difference θ of motor current calculated by the method as described above, angular velocity ω of sine wave specified by PWM control command by PWM control command, and previously stored in memory If the winding resistance value R and inductance L thus set are substituted into the above-described equation (15), the actual stroke ST of the mover at that time can be calculated.

  Further, in order to eliminate the influence of the magnetic saturation of the linear motor M, the microcomputer C of the present embodiment has a relationship between the induced voltage coefficient α and the effective value Φ of the total number of magnetic fluxes in the memory as shown in FIG. Is provided with a data table 105 in which approximate expression data or a data string indicating a correlation curve is stored. The correlation curve described above is obtained in advance by experiments.

  When calculating the actual stroke ST of the linear motor M, first, the effective value Φ of the total number of magnetic fluxes is calculated using the aforementioned equation (21). Next, the induced voltage coefficient α is corrected using the data table 105 in which the approximate expression or data string of the correlation curve stored in the memory is stored. Thereafter, the stroke ST in which the adverse effect of magnetic saturation of the linear motor M is eliminated is calculated using the corrected value of the induced voltage coefficient α.

  Another example of a linear motor control system may be configured as shown in FIG. Next, another example of the linear motor control system shown in FIG. 8 will be briefly described. Since the linear motor control system shown in FIG. 8 can obtain the same effect as the linear motor control system shown in FIG. 6, only different points will be described.

  In another example of the linear motor control system shown in FIG. 8, the motor voltage detection means W is provided between the DC power supply and the inverter circuit T. The DC power voltage signal detected by the motor voltage detection means W is transmitted to the motor voltage estimation unit 106 in the microcomputer C. The motor voltage estimation unit 106 estimates the effective value V of the motor voltage using the DC power voltage signal and the modulation rate command value data transmitted from the stroke control unit 102 to the motor voltage estimation unit 106. Then, the effective value V of the estimated motor voltage is transmitted from the motor voltage estimation unit 106 to the stroke calculation unit 104.

  On the other hand, the motor current detection means H has a Hall element and is provided between the inverter circuit T and the linear motor M. The motor current detection means detects a change in magnetic flux by the Hall element, and transmits the change in the magnetic flux to the stroke calculation unit 104 in the microcomputer C as a current signal of the motor current.

  Next, a stroke control process performed by the microcomputer C will be described with reference to FIGS. 9 and 10.

  In principle, the stroke control process is performed for each cycle of the linear motor operation. First, in S1, a voltage signal for one cycle, that is, an instantaneous value of the motor voltage v (t) [t = 1 to n] is received. At the same time, in S2, a current signal for one cycle, that is, an instantaneous value of the motor current i (t) [t = 1 to n] is received. That is, in S1 and S2, a voltage signal and a current signal that can specify a voltage waveform and a current waveform for one period are received. Next, in S3, the phase difference θ between the motor current i (t) and the motor voltage v (t) is calculated using the voltage signal and current signal for one cycle. Next, in S4, the angular velocity ω of the motor voltage v (t) or the motor current i (t) is calculated using the voltage signal or current signal for one cycle. However, the angular velocity ω may be a predetermined fixed value and a value stored in the memory.

  Next, in S5, the effective value V of the motor voltage and the effective value I of the motor current are calculated. In the process of S5, v (1), v (2),..., V (n−1), v (n) are sequentially compared in S52 shown in FIG. Next, in S53, the maximum value v (max) and the minimum value v (min) of v (1), v (2), ..., v (n-1), v (n) are determined. Next, in S54, the effective value V = {v (max) −v (min)} / 2√2 of the motor voltage is calculated. Next, in S55, i (1), i (2),..., I (n-1), i (n) are sequentially compared. Next, in S56, the maximum value i (max) and the minimum value i (min) of i (1), i (2), ..., i (n-1), i (n-1) are determined. Next, in S57, the effective value I of the motor current is calculated using Expression (22).

  Thereafter, the process of S6 in FIG. 9 is executed. In S6, the winding resistance value R and the inductance L are read from the memory. Next, in S7, the effective value V of the motor voltage, the effective value I of the motor current, the phase difference θ, the winding resistance value R, and the inductance L are substituted into the above-described equation (1), and the effective value E of the induced voltage is obtained. calculate.

Next, in S8, the effective value V of the motor voltage, the effective value I of the motor current, the effective value E of the induced voltage, the phase difference θ, and the winding resistance value R are substituted into the equation (10), and the phase difference θ ₂ Is calculated. In S9, the effective value E of the induced voltage, the effective value I of the motor current, the angular velocity ω, the inductance L, and the phase difference θ ₂ are substituted into the equation (21) to calculate the effective value Φ of the total number of magnetic fluxes. Next, in S10, the value of the induced voltage coefficient (thrust coefficient) α is corrected using the approximate expression data or the data table (FIG. 4) showing the effective value Φ of the total number of magnetic fluxes and the correlation curve.

  Next, in S11, the actual stroke ST of the mover is calculated by substituting the induced voltage coefficient α, the effective value E of the induced voltage, and the angular velocity ω into Equation (2). In S12, a difference D between the actual stroke ST and the stroke command value is calculated. Next, in S13, the PWM modulation rate is changed according to the difference D, and processing for bringing the actual stroke ST value closer to the stroke command value is executed. Thereafter, the processes of S1 to S13 are repeated every cycle.

  Next, a Stirling refrigeration system to which the above linear motor control system is applied will be described.

  FIG. 11 is a cross-sectional view showing the Stirling refrigerator 40 of the embodiment. In the Stirling refrigerator 40, a cylindrical piston 1 and a displacer 2 are fitted in a cylindrical cylinder 3 composed of two parts. The piston 1 and the displacer 2 are provided via a compression space 9 and have an axis Y as a common drive shaft.

  An expansion space 10 is formed on the tip side of the displacer 2. The compression space 9 and the expansion space 10 communicate with each other via a medium flow passage 11 through which a working medium such as helium flows. A regenerator 12 is provided in the medium flow path 11. The regenerator 12 accumulates the heat of the working medium and supplies the accumulated heat to the working medium. A flange (flange) 3 a is provided in the middle of the cylinder 3. A bounce space (back pressure space) 8 is formed in the collar portion 3a by being sealed with a dome-shaped pressure vessel 4 attached thereto.

  The piston 1 is integrated with the support spring 5 on the rear end side. The displacer 2 is integrated with the support spring 6 through a rod 2 a that passes through the center hole 1 a of the piston 1. The support spring 5 and the support spring 6 are connected by a bolt and a nut 22. As will be described later, when the piston 1 reciprocates, the displacer 2 reciprocates with a predetermined phase difference with respect to the piston 1.

  An inner yoke 18 is fitted on the outer peripheral side of the cylinder 3 in the bounce space 8. The inner yoke 18 faces the outer yoke 17 through a gap 19. A driving coil 16 is fitted inside the outer yoke 17. An annular permanent magnet 15 is movably provided in the gap 19. The permanent magnet 15 is integrated with the piston 1 through a cup-shaped sleeve 14. The inner yoke 18, the outer yoke 17, the driving coil 16, and the permanent magnet 15 constitute a linear motor 13 that moves the piston 1 along the axis Y. This linear motor functions as the linear motor M of the above-described linear motor control system. Further, lead wires 20 and 21 are connected to the driving coil 16, and driving power is supplied to the linear motor 13 by the inverter circuit 200 and the microcomputer 1000.

  In the Stirling refrigerator 40 having the above configuration, when the piston 1 reciprocates by the linear motor 13, the displacer 2 reciprocates with a predetermined phase difference with respect to the piston 1. As a result, the working medium moves between the compression space 9 and the expansion space 10. As a result, a reverse Stirling cycle is formed.

  When the drive voltage having a predetermined AC waveform is applied to the linear motor 13, the Stirling refrigerator 40 described above reciprocates with a cycle and a stroke corresponding to the drive voltage having the predetermined AC waveform. Therefore, by controlling the drive voltage applied to the linear motor 13, the cycle and stroke of the reciprocating motion of the piston 1 can be controlled.

  Next, the operation principle of the free piston type Stirling refrigerator will be described in more detail. As the piston 1 moves so that the relationship between its position and time draws a sine wave, the working gas in the compression space 9 changes so that the relationship between its pressure and time draws a sine wave, and compression. Heat is released from the space 9 and flows into the expansion space 10 while being cooled by the regenerator 12 provided around the displacer 2.

  The working gas in the expansion space 10 expands due to the movement of the displacer 2, and its temperature decreases. The working gas in the expansion space 10 changes so that the relationship between pressure and time draws a sine wave, and the displacer 2 is reciprocated with a predetermined phase difference with respect to the piston 1.

  Note that PWM is used to convert a digital signal into an analog signal. That is, the plurality of pulses sequentially output from the inverter circuit T are controlled so that the width thereof changes corresponding to the sine waveform, and an alternating current is generated. For this control, the microcomputer C, the inverter circuit T, and the AC power supply G and the smoothing circuit P constituting the DC power supply are used in the linear motor control system described above.

  According to the Stirling refrigerator control system using the linear motor control system of the present embodiment as described above, the stroke ST of the piston 1 as the mover becomes too large, and the piston 1 and the displacer 2 collide. Is reliably prevented. Further, the stroke of the piston can be controlled more strictly.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a figure which shows the equivalent circuit structure of a linear motor drive circuit. It is a figure which shows the change of one period of each instantaneous value of a motor voltage, a motor current, and an induced voltage. It is a vector diagram for calculating | requiring the effective value of the induced voltage which arises in a linear motor. It is a graph which shows the correlation of a total magnetic flux number and an induced voltage coefficient. It is a vector diagram for calculating | requiring the total magnetic flux number which arises in the magnetic circuit of a linear motor. It is a block diagram which shows the structure of a linear motor control system. It is a figure for demonstrating the method of calculating the effective value of a motor current using the maximum value and minimum value (peak value) of a motor current. It is a block diagram which shows the structure of the linear motor control system of another example. It is a flowchart for demonstrating a stroke control process. It is a flowchart for demonstrating a stroke control process. It is a figure which shows the Stirling refrigerating system using the linear motor control system.

Explanation of symbols

  M linear motor, G AC power supply, P smoothing circuit, H, S motor current detection means, T inverter circuit, U, W motor voltage detection means, C microcomputer.

Claims (5)

A linear motor in which the mover reciprocates;
Voltage detection means for detecting a motor voltage applied to the linear motor;
Current detecting means for detecting a motor current flowing in the linear motor;
A microcomputer that receives a voltage signal capable of specifying an instantaneous value of the motor voltage and a current signal capable of specifying an instantaneous value of the motor current;
The microcomputer is
Assuming that each of the motor voltage, the motor current, and the induced voltage (back electromotive force) generated by the reciprocating motion of the mover is a sine wave having the same angular velocity, the voltage signal and the current signal are used. Means for calculating an effective value of the induced voltage in one cycle of the sine wave;
A linear motor control system comprising: means for calculating a stroke of the mover in the one cycle using an effective value of the induced voltage, an angular velocity of the voltage signal and the current signal, and an induced voltage coefficient (thrust coefficient). . A linear motor in which the mover reciprocates;
Voltage detection means for detecting a motor voltage applied to the linear motor;
Current detecting means for detecting a motor current flowing in the linear motor;
A microcomputer that receives a voltage signal capable of specifying an instantaneous value of the motor voltage and a current signal capable of specifying an instantaneous value of the motor current;
The microcomputer is
Means for calculating a phase difference θ between the motor voltage and the motor current, and an angular velocity ω of the voltage signal and the current signal, using the voltage signal and the current signal;
Assuming that each of the motor voltage, the motor current, and the induced voltage (back electromotive force) generated by the reciprocating motion of the mover is a sine wave having the same angular velocity ω, the voltage signal and the current signal are used. Means for calculating an effective value V of the motor voltage and an effective value I of the motor current in one cycle of the sine wave;
Substituting the effective value V of the motor voltage, the effective value I of the motor current, the phase difference θ, the resistance value R of the linear motor, and the inductance L value of the linear motor into the following equation (1), the induced voltage Means for calculating an effective value E of

Means for substituting the effective value E of the induced voltage E, the angular velocity ω, and the induced voltage coefficient (thrust coefficient) α into the following equation (2) to calculate the stroke ST of the mover in the one cycle;

A linear motor control system. DC power supply,
An inverter circuit that is electrically connected between the DC power source and the linear motor and drives the linear motor;
A resistor connected between the DC power source and the inverter circuit;
The microcomputer calculates the maximum value and the minimum value within one cycle of the motor current by detecting an instantaneous value for one cycle of the potential difference between both ends of the resistor, and calculates the maximum value and the minimum value. The linear motor control system according to claim 2, wherein an effective value I of the motor current is calculated. A linear motor in which the mover reciprocates;
Voltage detection means for detecting a motor voltage applied to the linear motor;
Current detecting means for detecting a motor current flowing in the linear motor;
A microcomputer that receives a voltage signal capable of specifying an instantaneous value of the motor voltage and a current signal capable of specifying an instantaneous value of the motor current;
The microcomputer is
Using the voltage signal and the current signal, the angular velocity of those signals, the effective value of the induced voltage (back electromotive force) generated by the reciprocating motion of the mover, and the effective number of total magnetic fluxes generated in the magnetic circuit of the linear motor. Means for calculating a value;
An approximate expression or data table for specifying the relationship between the effective value of the total number of magnetic fluxes and the induced voltage coefficient (thrust coefficient);
Means for correcting the induced voltage coefficient using the effective value of the total number of magnetic fluxes and the approximate expression or the data table;
A linear motor control system comprising: means for calculating a stroke of the mover using the induced voltage, the angular velocity, and the corrected induced voltage coefficient. A linear motor control system according to any one of claims 1 to 4,
A Stirling refrigeration system comprising a displacer that reciprocates according to a reciprocating motion of a piston as the mover.

Images