KR100427477B1 - System for controlling speed of the gantry for computerized tomography equipment - Google Patents

Abstract

Speed control device for a gantry for a computed tomography device according to the present invention, the AC / DC conversion unit for converting an AC current into a DC current; A three-phase two-phase coordinate conversion unit for equivalently converting the converted direct current into a two-phase current on the d and q axes; A speed detector detecting a speed of the motor; A PI controller for performing proportional-integral control on the deviation between the reference speed and the detection speed; A limiter for limiting and outputting an amplitude of an input waveform; A control current compensator for compensating the control current input to the motor; A voltage command compensator for compensating a voltage command input to the motor; a two-phase-3 phase coordinate inverse transform unit which coordinate-converts the two-phase voltage on the d and q axes to a three-phase voltage; A pulse width modulator for modulating and outputting a pulse width of a three phase voltage; In the speed control apparatus of a synchronous motor having an inverter to control the operation of the motor by performing the on / off control for the three-phase voltage, the three-phase two-phase coordinate conversion unit between the limiter and the control current compensation unit The torque on the eccentric load is estimated by inputting the current on one of the two-phase currents on the d and q axes converted by the motor and the speed of the motor detected by the speed detector, and estimated by the predetermined algorithm. An eccentric load torque estimator is further provided.

Description

System for controlling speed of the gantry for computerized tomography equipment}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed control device for a gantry for a computed tomography device. In particular, an eccentric load estimator is added to a general vector control system for speed control of a surface-mounted permanent magnet synchronous motor. The present invention relates to a speed control device for a gantry for a computed tomography device that calculates a compensation current interlocked with a phase and then adds the compensation current to a drive current component to reduce a speed ripple remaining even in a normal operating state.

In general, the gantry used in the computed tomography apparatus is equipped with an X-ray tube, an X-ray detector, a temperature controller, a high pressure generator, a slip ring, and the like, and the gantry rotates while the devices are mounted. The specification required for such a gantry is to be able to control the variable speed at a constant speed, to control the speed up to a high speed range to obtain more image information per unit time, and to have a uniform speed quality.

By the way, the devices mounted on the computed tomography apparatus are made for different purposes, and it is very important to mount such apparatuses so as not to have an eccentricity on the surface of the gantry for the computed tomography apparatus having different weights. It is difficult. Therefore, sometimes a dummy weight is used to balance the weight, and thus there is a limit to adjusting the balance.

The gantry for a computed tomography apparatus having an eccentric load as described above has a limitation in speeding up because a high speed ripple appears when the driving speed increases. In addition, the method of removing the eccentric load component by hand in the manufacturing step is effective up to a certain level, but it is very difficult to adjust the speed ripple to zero in normal state.

1 is a view showing a system configuration of a speed control apparatus of a synchronous motor to which a conventional general vector control technique is applied.

Referring to FIG. 1, a speed control apparatus for a synchronous motor to which a conventional general vector control technique is applied takes any two phases (for example, u and v phases) among three phase alternating currents applied to the PMSM 100. The motor current detected by the counter 130 is an AC / DC converter 101 (102) for converting an AC current into a DC current, and a DC current converted by the AC / DC converter (101) (102). A three-phase two-phase coordinate conversion unit 103 for equivalently converting two-phase currents on the d and q axes based on the former phase θ information, and a signal from the encoder 120 to receive the motor 99. A speed detector 104 for detecting a speed of Speed detected by the speed detector 104 in The PI controller 105 performs a proportional-integral control based on the result of subtracting the result of the subtraction, the output of the PI controller 105 and the speed detected by the speed detector 104 ( ) And the q-axis reference current ( Limiter 106 for outputting the reference current and the reference current on the d, q axis ( , ) And the two-phase current (d, q-axis) converted by the three-phase two-phase coordinate conversion unit 103 , ) And compensating the control current by comparing each other, while the reference voltage on d, q axis ( , ) And a reference voltage from the control current compensator 107 , ) Is a voltage command compensator 108 for compensating and outputting a voltage command and a two-phase voltage command compensating voltage on the d and q axes input from the voltage command compensator 108. , ) Is converted into a three-phase voltage based on the phase (θ) information of the motor rotor detected by the counter 130 to convert the three-phase reference voltage ( , , ) And the three-phase reference voltage from the two-phase three-phase coordinate inverse transform unit 109 and the two-phase three-phase coordinate inverse transform unit 109 , , ) And a pulse width modulator 110 for modulating and outputting the pulse width of each of the three phase voltages, and on / off control of the three phase voltage input through the pulse width modulator 110. It consists of an inverter 111 to control the operation of the electric motor 100 by performing.

On the other hand, by the speed control system of the synchronous motor to which the conventional vector control technique as described above, the speed ripple can be reduced to some extent, as shown in Figure 2, the speed even in the normal operation state by the eccentric load of the gantry You can see the ripple remaining.

The present invention has been made in view of the above, and by adding an eccentric load estimator to a general vector control system, a speed ripple can be reduced by adding a compensating current interlocked with the magnitude and phase of an eccentric load to a driving current component. It is an object of the present invention to provide a speed control device of a gantry for a computed tomography device.

1 is a schematic system configuration diagram of a speed control apparatus of a synchronous motor to which a conventional general vector control technique is applied.

FIG. 2 is a view showing a speed ripple generated in a normal operating state when controlled by the speed controller of FIG. 1. FIG.

Figure 3 is a schematic system configuration of the speed control device of the gantry for a computed tomography device according to the present invention.

4 shows a torque estimation algorithm in an eccentric load torque estimator of the speed control device of FIG.

5 is a view showing eccentric load torque characteristics during control by the speed controller of FIG.

FIG. 6 is a diagram showing speed characteristics in a steady state due to an eccentric load during control by the speed controller of FIG. 1; FIG.

7 shows eccentric load torque and estimated eccentric load torque characteristics during control by the speed controller of FIG.

8 is a view showing eccentric load torque and compensation current during control by the speed controller of FIG.

9 is a diagram showing speed characteristics in a steady state due to an eccentric load during control by the speed controller of FIG.

<Explanation of symbols for the main parts of the drawings>

101,102,301,302 ... AC / DC converter 103,303 ... Coordinate converter

104,304 ... Speed detector 105,305 ... PI controller

106,306 ... Limiter 107,309 ... Control current compensation

108,310 ... Voltage command compensator 109,311 ... Coordinate inverse converter

110,312 ... pulse width modulator 111,313 ... inverter

120,320 ... Encoder 130,330 ... Counter

307 ... Eccentric Load Torque Estimator ... 308 Torque-to-Current Converter

100 ... Synchronous Motor 300 ... Gantry

In order to achieve the above object, the speed control device for a gantry for a computed tomography device according to the present invention,

An apparatus for controlling the speed of a synchronous motor provided in a gantry for a computed tomography device, comprising: an alternating current / direct current converting unit for converting an alternating current for two phases of three-phase alternating current applied to the motor into a direct current; A three-phase two-phase coordinate conversion unit for equivalently converting the converted direct current into a two-phase current on the d and q axes; A speed detector detecting a speed of the motor; A PI controller for performing proportional-integral control on the deviation between the reference speed and the detection speed; A limiter for limiting and outputting an amplitude of an input waveform; A control current compensator for compensating the control current input to the motor; A voltage command compensator for compensating a voltage command input to the motor; a two-phase-3 phase coordinate inverse transform unit which coordinate-converts the two-phase voltage on the d and q axes to a three-phase voltage; A pulse width modulator for modulating and outputting a pulse width of each voltage of three phases; In the speed control apparatus of a synchronous motor having an inverter for controlling the operation of the motor by performing on / off control for the three-phase voltage input to the motor,

Between the limiter and the control current compensator, the current on any one of the two-phase currents on the d and q axes converted by the three-phase two-phase coordinate converter and the speed of the motor detected by the speed detector. Input algorithm And This feature is characterized in that an eccentric load torque estimator is further provided for estimating the torque according to the eccentric load and outputting the torque estimation value.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a view schematically showing a system configuration of a speed control apparatus of a gantry for a computed tomography apparatus according to the present invention.

3, the speed control device of the gantry for a computed tomography device according to the present invention has a system configuration of the speed control device of the synchronous motor to which the conventional general vector control method of FIG. In addition, an eccentric load torque estimator 307 is further provided. Preferably, the apparatus further includes a torque-to-current converter 308 that receives the output from the eccentric load torque estimator 307 and converts it into a current.

That is, the speed control device of the gantry for computer tomography device according to the present invention is any two-phase (for example, u) of the three-phase AC applied to the electric motor (not shown) installed in the gantry 300 for the computer tomography device. AC / DC converters 301 and 302 for taking the phase V and converting the AC current into DC currents, and the DC currents converted by the AC / DC converters 301 and 302 to counter. From the encoder 320 and the three-phase two-phase coordinate conversion unit 303 for equivalently converting the two-phase currents on the d and q axes, respectively, based on the phase (θ) information of the motor rotor detected by 330. Speed detection unit 304 for receiving a signal to detect the speed of the motor in the gantry 300, and the reference speed ( Speed detected by the speed detection unit 304 in The PI controller 305 performs proportional-integral control based on the result of subtracting the result of subtraction), the output of the PI controller 305, and the speed detected by the speed detector 304. ), The limiter 306 outputs the amplitude of the input waveform by limiting the amplitude of the input waveform, and the one of the two-phase currents of the two-phase currents of the d and q axes converted by the three-phase two-phase coordinate conversion unit 303 ( For example, on the q-axis ) And the speed of the motor detected by the speed detection unit 304 ( ), The torque according to the eccentric load is estimated by a predetermined algorithm, and the torque estimation value ( Torque estimation value from the eccentric load torque estimator 307 and the eccentric load torque estimator 307 ), The reference current on the q-axis obtained by the sum of the torque-current converter 308 that receives the input and converts it into a current, and the output of the limiter 306 and the output of the torque-current converter 308 ( ) And the reference current on the d-axis input from an external device ( ) And the two-phase current (d, q-axis) converted by the three-phase two-phase coordinate conversion unit 303 ( , ) To compensate for the control current by receiving each input and compare the reference voltage on the d and q axes. , ) And a reference voltage from the control current compensator 309 , ) And a voltage command compensator 310 for compensating and outputting a voltage command, and a two-phase voltage command compensating voltage on the d and q axes input from the voltage command compensator 310. , ) Is converted into a three-phase voltage based on the phase (θ) information of the motor rotor detected by the counter 330 to convert the three-phase reference voltage ( , , 3 phase reference voltage from the 2 phase-3 phase coordinate inverse transform unit 311 and the 2 phase-3 phase coordinate inverse transform unit 311 , , ), The pulse width modulator 312 for modulating and outputting the pulse width of each of the three phase voltages, and the on / off control of the three-phase voltage input through the pulse width modulator 312 It consists of an inverter 313 to control the operation of the gantry 300 by performing.

In the speed control apparatus of the gantry for a computed tomography device according to the present invention having the configuration as described above, the electric torque and the mechanical for the electric motor (for example, surface-mounted permanent magnet synchronous motor) installed in the gantry 300 The general torque is given by the following formula.

On the other hand, since the sampling time in the current control is about 100 ms, the load torque within one sampling time can be assumed to be constant. When the equations 1 and 2 are summarized with respect to the speed, Equation can be obtained.

In addition, if Equation 3 is expressed in discrete time, it may be expressed as follows.

Based on Equations 4 and 5, if the load estimator is constructed using the minimum dimensional observer, it can be expressed as Equation 6 and Equation 7 below.

In addition, the equation (6) and the observer gain (K _e) of the expression (7) can be calculated by the following formula relationship.

FIG. 4 shows a torque estimation algorithm in the eccentric load torque estimator 307 in the system configuration of the speed control apparatus of the gantry for a computed tomography apparatus according to the invention of FIG. Fig. 7 shows the process of estimating the load torque generated by eccentric load by plotting the calculation process in the form of signal input / output.

5 and 6 are graphs of eccentric load torque and speed characteristics of the synchronous motor to which the conventional general vector control method of FIG. 1 is applied, and FIGS. 7 to 9 are computerized tomography apparatuses according to the present invention. This is a graph of eccentric load torque, compensation current and speed characteristics by the speed control device of the gantry.

It can be seen that with respect to the applied eccentric load torque as shown in FIG. 5, in the case of control by the conventional synchronous motor speed control device, as shown in FIG. 6, a speed ripple occurs in a normal operation state.

However, in the case of the control by the speed control device to which the eccentric load torque estimator of the present invention is added, the current component corresponding to the eccentric load is compensated for in the eccentric load torque as shown in FIG. Therefore, as shown in FIG. 9, it can be seen that the speed ripple can be almost completely removed to obtain a DC state.

As described above, the speed control device of the gantry for the CT apparatus according to the present invention adds an eccentric load estimator to a general vector control method for speed control of a synchronous motor to compensate for interlocking with the size and phase of the eccentric load. After calculating the current, the compensation current is added to the drive current component, so that the remaining velocity ripple can be almost completely eliminated even in the normal operating state. Therefore, it is applicable to all fields requiring high precision speed control, such as control of high precision CT gantry, control of motor vehicle motor which can give a smooth ride feeling to passenger fluctuation, control of motor for machine tool which requires high quality machining, High quality speed control effect can be obtained.

Claims (2)

An apparatus for controlling the speed of a synchronous motor provided in a gantry for a computed tomography device, comprising: an alternating current / direct current converting unit for converting an alternating current for two phases of three-phase alternating current applied to the motor into a direct current; A three-phase two-phase coordinate conversion unit for equivalently converting the converted direct current into a two-phase current on the d and q axes; A speed detector detecting a speed of the motor; A PI controller for performing proportional-integral control on the deviation between the reference speed and the detection speed; A limiter for limiting and outputting an amplitude of an input waveform; A control current compensator for compensating the control current input to the motor; A voltage command compensator for compensating a voltage command input to the motor; a two-phase-3 phase coordinate inverse transform unit which coordinate-converts the two-phase voltage on the d and q axes to a three-phase voltage; A pulse width modulator for modulating and outputting a pulse width of each voltage of three phases; In the speed control apparatus of a synchronous motor having an inverter for controlling the operation of the motor by performing on / off control for the three-phase voltage input to the motor, Between the limiter and the control current compensator, the current on any one of the two-phase currents on the d and q axes converted by the three-phase two-phase coordinate converter and the speed of the motor detected by the speed detector. Input algorithm And And an eccentric load torque estimator for estimating the torque according to the eccentric load and outputting the estimated torque value thereof. The method of claim 1, The rear end of the eccentric load torque estimator further comprises a torque-to-current converter for receiving the torque estimation value from the eccentric load torque estimator to convert the current into a current, the speed control device for a computer tomography apparatus.