JP5949144B2 - Centrifuge - Google Patents

Description

  The present invention relates to control of a motor that rotates a rotor of a centrifuge (centrifugal separator), and more particularly to a technique for suppressing vibration during acceleration / deceleration of a centrifuge using an induction motor.

  A centrifuge is a device that performs a sample separation operation using centrifugal force by rotating a rotor containing a sample at high speed. The rotor used is detachable and often replaceable. When the sample is separated by the centrifuge, the operator sets centrifugal conditions such as the rotational speed of the rotor, the operation time, and the temperature of the rotor chamber according to the purpose of separating the sample from input means such as an input panel. The centrifuge accelerates or decelerates the rotor according to the set centrifugal conditions to maintain a predetermined rotational speed, and decelerates and stops the rotor when the set operation time has elapsed or when a stop operation is performed by the user. To do.

  FIG. 1 is a cross-sectional view schematically showing the overall configuration of a centrifuge according to a conventional example. The centrifuge 1 includes a rotation chamber 5 inside the main body, the rotation chamber 5 is closed by a door 3, and a motor 4 is provided below the rotation chamber 5 as a drive source. A shaft (output shaft) 16 that transmits rotational torque from the motor 4 extends so as to protrude into the rotary chamber 5, and the rotor 2 is set on a crown 17 provided at the tip of the shaft 16. Since the rotor 2 is set at the tip of the shaft 16 of the motor 4 in this way, the rotational driving force by the motor 4 is directly transmitted to the rotor 2. A substantially cylindrical shaft case 14 is disposed around the shaft 16 to prevent moisture and the like from entering the motor 4. The cooling device 18 cools the inside of the rotating chamber 5 by flowing a refrigerant through a cooling pipe 18a wound around the outer periphery of the chamber 13, and a refrigeration cycle using a refrigerant such as Freon gas is used. There are various types of compressors for the refrigeration cycle, but it is preferable to install a variable speed compressor using an inverter because the cooling capacity can be improved. The control device 7 drives and controls the cooling device 18 based on the temperature of the rotating chamber 5 detected by the temperature sensor 15, and controls the rotating chamber 5 to a predetermined temperature. A heat insulating material (not shown) is provided around the chamber 13 and the cooling pipe 18 a and inside the door 3 that closes the rotating chamber 5.

  Conventionally, an induction motor (induction motor), particularly a three-phase induction motor, has been widely used as the motor 4 that rotationally drives the rotor 2. The induction motor includes a stator-side coil and a rotor having a squirrel-cage conductor, and the stator-side coil operates by transmitting energy to the rotor conductor by electromagnetic induction. In centrifuges, the rotor 2 is often mounted directly on the rotating shaft of the motor 4 without being decelerated / accelerated by gears or belts. In this case, the rotational speed of the motor 4 and the rotor 2 are often driven. The number of rotations is the same. A drive circuit for the motor 4 is disposed in the control device 7 and a three-phase AC inverter (not shown) capable of variably controlling voltage and frequency is used. The output voltage of the three-phase AC inverter generates a pseudo sine wave voltage by a PWM (pulse width modulation) method.

In a three-phase induction motor, a three-phase AC inverter applies a three-phase alternating current to the stator winding to generate a rotating magnetic field in the motor, and the rotating magnetic field generates an induction current in the rotor in the motor, and their interaction To generate torque. Therefore, a speed difference called “slip” occurs between the speed of the rotating magnetic field and the speed of the rotor. The slip is expressed by (Equation 1). If the slip is positive, a positive torque (acceleration torque) is generated in the rotation direction on the output shaft of the motor 4, and if the slip is negative, a negative torque (braking) in the rotation direction is generated. Torque) is generated.
Slip = rotational speed of rotating magnetic field-rotational speed of rotor ... (Equation 1)
Some three-phase induction motors have two, four, or more poles depending on the winding method. If the number of poles is P, the rotation speed of the rotating magnetic field is 2 / P times the excitation speed given from the three-phase AC inverter. Therefore, for example, in the case of a two-pole three-phase induction motor, the rotation speed of the rotating magnetic field is It matches the speed (excitation frequency). In this case, (Equation 1) can be replaced with the following (Equation 2).
Slip = Excitation speed-Rotor rotation speed (2)

  In general, sensorless control is applied to drive a three-phase induction motor. However, in a centrifuge, a rotation sensor (described later) is often provided in order to control the rotation speed more accurately. The control device 7 includes a three-phase AC inverter whose output voltage is variable by PWM control, and generates a three-phase AC with a predetermined voltage and a predetermined frequency based on the rotation speed of the motor obtained by the rotation sensor. Applied to the motor 4.

The relationship between the excitation speed and the rotation speed of the motor 4 in the conventional centrifuge 1 as described above will be described with reference to FIGS. In the following description, the number of poles of the motor is two, that is, the case where the rotation speed of the rotating magnetic field coincides with the excitation speed, that is, it is assumed that (Equation 2) can be applied. In FIG. 6, the horizontal axis indicates the passage of time, and the vertical axis indicates the voltage applied from the control device 7 to the motor 4 (unit V), the excitation speed (unit rpm), and the rotation speed (unit rpm) of the motor 4. ing. Centrifuge 1 at time _{t 0,} it is assumed that operating at a rotational speed set 20000 rpm (settling state). At this time, the excitation speed 252 is higher than the rotational speed 251 of the motor 4 and a positive slip occurs. When a predetermined operation time set in advance at time t ₁ has elapsed or when a stop operation is performed by the user and a shift to deceleration control is started, the excitation speed 252 gradually decreases as indicated by an arrow 252a, At the arrow 252b, the rotational speed becomes equal to the rotational speed 251, and thereafter, as shown by the arrow 252c, a negative slip is maintained while the excitation speed 252 remains below the rotational speed 251. When the slip changes from positive to negative, even if a voltage slightly higher than 200 V or 200 V is applied to the motor 4, the current flowing through the motor 4 as the slip decreases due to the characteristics of the induction motor (non- When the slip becomes zero and the current is minimized to near zero, the motor current increases again as the negative slip increases. Due to this negative slip state, the motor 4 enters a braking state and is decelerated at a predetermined deceleration rate. At the same time, the applied voltage 253 is changed toward a predetermined value for deceleration control. Here, in the set state of the motor 4, the applied voltage is suppressed to a state slightly lower than the rating as indicated by an arrow 253a.

Exciting speed 252 at time t ₂ in the deceleration control becomes a value resulting a predetermined negative slip, the applied voltage 253 is the rotor 2 sufficient braking torque when a predetermined value is generated to decelerate. Even during deceleration, the control device 7 sequentially detects the rotational speed 251 and performs control so as to apply to the motor 4 an excitation speed 252 that generates a predetermined slip determined for each rotational speed and a predetermined applied voltage 253. To do. The lower side of FIG. 6 shows the magnitude of the applied voltage 253, the vertical axis represents the applied voltage [V], and the horizontal axis represents the passage of time. In general, the acceleration / deceleration control of the induction motor is V / F control in which the ratio between the excitation speed and the applied voltage is substantially constant. In the conventional example shown here, the applied voltage is slightly reduced during deceleration as indicated by the arrow 253b. rises, sometimes the upper limit value of the constraint by an applied voltage, such as the withstand voltage of circuit components is limited, is the applied voltage as shown by the arrow 253c during the period from the time t ₂ in FIG. 6 to t ₃ is constant This is due to the limitation of the upper limit value. When the rotational speed 251 reaches N ₀ at time t ₄ , the control device 7 switches the frequency of the excitation speed 252 to zero, that is, so-called DC braking in which direct current is applied to the motor 4, and continues until the rotational speed 251 becomes zero, deceleration control is terminated at time t _5.

Next, the transition from the deceleration control to the constant speed control at a predetermined rotational speed in the centrifuge according to the conventional example will be described with reference to FIG. The vertical and horizontal axes in FIG. 7 are the same as those in FIG. 6 described above. Excitation rate 262 as shown at time t ₀ the arrow 262a in the deceleration of the motor 4 is lower than the rotation speed 261, the negative slippage occurs. When the excitation speed 262 reaches a set excitation speed M ₂ that is a value obtained by adding a predetermined positive slip to the target rotational speed N ₂ of the motor 4 at time t ₁ , the control device 7 determines that the excitation speed 262 becomes M ₂ . controlled to maintain the rotational speed 261 cross the exciting speed 262 at arrows 262b, positive slip speed N ₂ is decelerated until it caused the constant positive torque is generated needed for the excitation rate M ₂ Fast driving.

After shifting to the constant speed operation, the control device 7 maintains a predetermined applied voltage, feeds back the rotation speed 261, appropriately increases / decreases or maintains the excitation speed 262, and the rotation speed 261 maintains N _2. The constant speed operation is controlled at the same time. A technique for controlling the slip by detecting the rotational speed of the motor in this way is disclosed in Patent Document 1.

Japanese Patent Laid-Open No. 9-74784

  As described in the example of FIG. 6 above, when the centrifuge (centrifuge) starts to decelerate from the state where the predetermined rotation speed is maintained, the change in the rotation speed of the rotating magnetic field applied to the three-phase induction motor by the inverter is changed. Will cause the slip state to transition from positive to negative. This transition process includes a period during which the motor torque is minimized, and depending on the motor structure and rotor shape, vibration may occur during this period, resulting in a slight increase in noise, or the engagement between the rotor and motor. May cause inconveniences such as wear. In addition, since the slip changes from a negative state to a positive state when the rotor is decelerated as described with reference to FIG. 7 and the constant speed control is maintained to maintain the predetermined rotational speed, the torque is minimized even during this transition process. There is a problem that vibration is likely to occur as in the example shown in FIG.

  In the control of a single induction motor, the problem that vibration is likely to occur when the load is light or no load has been known for a long time, and the vibration in the operations of FIGS. It is because it became a state. In a general induction motor, a predetermined excitation speed is applied to the induction motor. Therefore, as the load becomes lighter, the rotation speed increases and approaches the excitation speed. As a result, the slip becomes small and vibration occurs. . As a technique for suppressing this vibration, a technique for actively suppressing vibration by detecting a change in current has been proposed. However, such active suppression of vibration requires a complicated and high-speed processing for the microcomputer included in the control device, leading to an increase in product cost. For this reason, conventional centrifuges have taken countermeasures not by control, but by mechanical improvements such as improvement of the suspension structure of the motor, shock-absorbing members, and strengthening of the fitting portion between the motor and the rotor.

  The present invention has been made in view of the above background, and an object of the present invention is to provide a centrifuge that reduces noise and extends its life by smoothly controlling the rotation of an induction motor.

  Another object of the present invention is to provide a centrifuge that reduces the occurrence of vibration of the induction motor when the torque changes between positive and negative.

  Another object of the present invention is to provide a centrifuge that is less likely to generate vibration during rotation speed change even under light load and no load.

  The characteristics of representative ones of the inventions disclosed in the present application will be described as follows.

  According to one aspect of the present invention, a centrifuge having a rotor that holds a sample, a motor that rotationally drives the rotor, a rotation sensor that detects the rotational speed of the rotor or the motor, and a control device that controls the rotation of the motor. The motor is an induction motor, and the control device includes a variable voltage variable frequency type inverter by pulse width modulation, and includes an inverter for driving the motor. When changing the rotation speed of the rotating magnetic field supplied to the motor by the inverter from a state higher than the motor rotation speed to a lower state, or when changing from a state lower than the motor rotation speed to a higher state, The controller changes the state after reducing the output voltage of the inverter at a predetermined ratio relative to the output voltage before the start of the change. The state in which the output voltage is reduced is a voltage that is 3/4 or less of the output voltage (effective value) immediately before the change, preferably a voltage that is 1/2 or less, and more preferably approximately zero voltage.

According to another feature of the present invention, the reduction of the output voltage of the inverter is maintained in a predetermined range before and after the point in time when the rotation speed of the motor matches the rotation speed of the generated rotating magnetic field. The inverter adjusts the voltage applied to the motor when the rotation speed of the rotating magnetic field is switched by pulse width modulation, and the control device slips from the difference between the rotation speed obtained from the rotation sensor and the excitation speed by the inverter. Calculate and control the output voltage of the inverter. The rotor may be detachable, and the control device may be configured to identify the type of the mounted rotor and determine a reduction ratio of the output voltage of the inverter in accordance with the characteristics of the mounted rotor.

According to the first and second aspects of the present invention, when the rotational speed (excitation speed, excitation frequency) of the rotating magnetic field is switched from the upper side to the lower side or from the lower side to the upper side of the rotational speed of the motor, the control device is an inverter. The output voltage is reduced at a predetermined ratio, so that vibrations that occur when the slip is reduced can be reduced, noise increases, and the rotor / motor fitting part wears out. Can be suppressed.
According to the third and fourth aspects of the invention, since the reduced state is a voltage that is ½ or less of the output voltage immediately before the change, it occurs when the slip is smaller than the output voltage immediately before the change. Vibration can be greatly reduced.
According to the invention of claim 5, since the reduction state of the output voltage of the inverter is maintained at a predetermined time before and after the time when the excitation speed is switched with respect to the rotation speed , the occurrence of vibration before and after the switching at which vibration is likely to occur. Can be reduced.
According to the invention of claim 6, since the inverter adjusts the output voltage (applied voltage) when the slip becomes small by pulse width modulation, it can be realized by changing the software as it is in a general inverter circuit, The present invention can be realized with greatly reduced cost.
According to the seventh aspect of the present invention, since the control device can accurately calculate the slip, it is possible to output electric power of an appropriate frequency from the inverter regardless of the magnitude of the inverter voltage.
According to the eighth aspect of the invention, since the control device determines the reduction ratio of the output voltage of the inverter according to the identified type, it is possible to realize fine motor rotation control in accordance with the rotor.

It is sectional drawing which shows the outline of the whole structure of the centrifuge 1 which concerns on this invention and a prior art example. It is a schematic block diagram of the centrifuge which concerns on the Example of this invention. It is a graph which shows the change of the rotational speed of a motor, the excitation speed, and the applied voltage at the time of the motor shifting from the constant speed operation to the deceleration operation of the centrifuge according to the embodiment of the present invention. It is a graph which shows the change of the rotational speed of a motor, the excitation speed, and the applied voltage when the motor transfers to the constant speed driving | operation of the centrifuge which concerns on the Example of this invention. It is a flowchart which shows the motor control procedure at the time of the rotation change of the motor of the centrifuge which concerns on the Example of this invention. It is a graph which shows the rotation speed of a motor, the excitation speed, and the change of an applied voltage at the time of a motor shifting from constant speed operation to deceleration operation in the centrifuge of a prior art example. It is a graph which shows the change of the rotational speed of a motor, an excitation speed, and an applied voltage when the motor transfers from a deceleration operation to a constant speed operation in the centrifuge of a prior art example. It is a characteristic diagram of the induction motor showing the relationship between the applied voltage and torque when the excitation speed F is constant. FIG. 6 is a characteristic diagram of an induction motor showing the relationship between applied voltage and torque when slip is near zero when the excitation speed F is constant.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same parts as those in the conventional example are denoted by the same reference numerals, and repeated description is omitted. The inventors of the present application estimate the cause of the vibration of a centrifuge using a conventional induction motor, and can solve the problem with a relatively easy control method by a technical solution different from the known example in induction motor control. Thought. The hardware configuration of the centrifuge 1 in the present embodiment is the same as that shown in FIG. However, in this embodiment, the rotation control method of the motor 4 by the control device 7 is different from the conventional one.

First, in order to describe the configuration of the control device 7 according to the present embodiment, the relationship between the applied voltage and torque in the induction motor will be described with reference to FIGS. 8 and 9. FIG. 8 is a characteristic diagram showing a relationship between applied voltage and torque when the excitation speed (excitation frequency) F applied to the induction motor is constant, and is widely known as a characteristic diagram of the induction motor. The applied voltage here refers to the effective value of the alternating voltage applied between the lines of the motor, the horizontal axis indicates the rotational speed of the motor, and the vertical axis indicates the torque generated in the motor. Symbols V ₁ , V ₂ , and V ₃ indicate applied voltages. For example, V ₁ is 50 V _rms , V ₂ is 100 V _rms , and V ₃ is 200 V _rms , such that V ₁ <V ₂ <V ₃ .

Excitation rate F in FIG. 8, when the applied voltage is V _3, the rotational speed when the no-load is consistent with the excitation rate F, but the rotational speed by the load is reduced, when the load and balance torque of the Tn maintains constant speed operation where decreased speed by slip S ₃ with respect to F. When the applied voltage is V ₂ , the rotation speed decreases to a point where S ₂ occurs with respect to F, and the constant speed operation is maintained. Further, if the applied voltage is V ₁ , the speed is lowered until the slip reaches S ₁ and the constant speed operation is maintained. In this way, since the motor 4 rotates at a rotation speed at which a torque Tn that balances with the load is generated, even if the excitation speed F is the same, the rotation speed of the motor 4 that is balanced changes according to the applied voltage. .

FIG. 9 is an enlarged view of the vicinity of the zero slip of FIG. To make the graph easier to read omitted applied voltage V _2, it is shown only the applied voltage V ₁ and V _3. When the slip is zero, the torque is zero even if the applied voltage is V ₃ or V ₁ , but as can be seen from the figure, the slope of the characteristic curve, that is, the rate of change of the torque with respect to the change in the rotational speed differs depending on the applied voltage. . Therefore, the torque change when the rotation speed changes by Δn is only Δt ₁ at the applied voltage V ₁ , but becomes Δt _{3 at the} applied voltage V ₃ , and the higher the applied voltage, the more the rotation speed varies. The amount of change in torque also increases. Therefore, when the applied voltage is high, a slight change in rotational speed causes a large torque change and causes the rotational speed to pulsate. It is thought to be vibration.

  The inventors predicted that the vibration of the induction motor at light load / no load can be suppressed if the applied voltage is reduced to such an extent that the required torque can be obtained based on the above estimation. However, if the applied voltage is lowered in the control of a general induction motor, the possibility of stalling / stepping out when the load changes increases, so it is difficult to say that it is preferable control. In particular, in the case of an induction motor in which sensorless control without using a rotation sensor is general, stall and step-out cannot be detected quickly, making it difficult to appropriately respond to load fluctuations. For this reason, it was common knowledge that the control for reducing the applied voltage is not performed by a general induction motor, but the inventors thought that it is not necessary to be caught by this common sense in a centrifuge. That is, in the centrifuge, the rotation object only rotates the rotor holding the sample and the load hardly changes, and a rotation sensor for directly detecting the rotation shaft of the motor or the number of rotations of the rotor is also provided. For this reason, not only during constant speed operation, acceleration, and deceleration control, but also during the transitional period when the slip is positive and negative, it is possible to accurately grasp the slip and rotation speed, and to accurately control the applied voltage according to the slip value. It was considered possible and the present invention was reached.

  FIG. 2 is a schematic block diagram of the centrifuge according to the present embodiment. The motor 4 is a three-phase induction motor, and the number of poles of the motor 4 is two, that is, the rotation speed of the rotating magnetic field matches the excitation speed. The motor 4 may have four or more poles. In such a case, the rotational speed of the rotating magnetic field is 2 / P times the excitation speed (where P is the number of poles). The same explanation is possible. The control device 7 includes an inverter 10 that supplies driving power supplied to the motor 4, a rectifier 9 that rectifies the commercial power supply 20, and a smoothing capacitor 11 that is connected in parallel with the rectifier 9 and the inverter 10. Composed. The inverter 10 includes a plurality of FETs (field effect transistors), makes the output voltage variable by PWM control, and supplies an alternating current with a predetermined frequency to the V phase, U phase, and W phase of the induction motor. By supplying, the motor 4 is rotationally driven. The arithmetic unit 8 controls the entire centrifuge 1 and includes a microcomputer (not shown) and a storage device such as a ROM / RAM. The arithmetic unit 8 controls the output voltage, the power factor of the received power, the reverse flow of the regenerative energy to the power source accompanying the deceleration of the motor 4, and the like with respect to the rectifier 9. By supplying a signal (drive signal) to the gate of the transistor) at an appropriate timing for an appropriate time, an alternating current having a predetermined frequency is supplied to the V phase, U phase, and W phase of the induction motor. The magnitude of the AC voltage can be controlled by performing PWM control. A rotation sensor 12 using a known mechanism such as a Hall IC or a photo sensor is provided in the vicinity of the rotation axis of the motor 4, and the calculation unit 8 rotates the rotation speed (rotation frequency) of the motor 4 based on the output of the rotation sensor 12. Can be obtained. The arithmetic unit 8 performs feedback control so as to supply a drive current having an appropriate excitation speed according to the rotational speed of the motor 4. The calculation unit 8 is not only for controlling the motor 4 but also for starting and stopping a vacuum pump (not shown), driving control for the cooling device, displaying information on the operation display unit 6 and acquiring input data, etc. Performs overall control accompanying the operation.

FIG. 3 is a graph showing changes in the rotational speed, excitation speed, and applied voltage of the motor 4 when the motor 4 shifts from the constant speed operation to the deceleration operation in the centrifuge 1 according to the present embodiment. In this embodiment, since the number of poles of the motor 4 is two, the rotational speed of the rotating magnetic field matches the excitation speed. The horizontal axis of the graph indicates the passage of time, and the vertical axis indicates the voltage applied from the control device 7 to the motor 4, the excitation speed, and the rotation speed (rpm) of the motor. Centrifuge at time _{t 0,} running at a rotational speed set 20000 rpm. At this time, the excitation speed 52 is slightly higher than the rotation speed 51, and a positive slip occurs.

When a predetermined operation time set in advance at time t ₁ has passed (completion of a predetermined centrifugal operation) or when a stop operation is performed by the user and a shift to deceleration control is started, the excitation speed 52 is determined at that time. The applied voltage 53 is reduced as indicated by the arrow 53a. Although the applied voltage 53 can be reduced by PWM control of the inverter 10, the speed of the applied voltage 53 is reduced so quickly that torque is not reduced due to the voltage drop and inappropriate vibration does not occur, for example, 200V to 0V. It may be performed in about 0.5 seconds to decrease to the vicinity. Applied voltage 53 is a predetermined value in the arrow 53b (here, approximately zero voltage) was lowered to, after a slight waiting time (time a) has elapsed, arrows excitation rate 52 from the state of arrow 52a at time t ₂ The value is reduced to the state of 52b to a value that causes a predetermined negative slip with respect to the rotational speed 51. Here, the standby time a is provided because the torque is zero when the excitation speed 52 crosses the rotational speed 51, and vibration is likely to occur before and after that, and it is desired to avoid the vibration as much as possible. . Here, the speed at which the excitation speed 52 is decreased from the arrows 52a to 52b may be set to a speed that does not cause inappropriate vibration due to the torque changing from positive to negative, and ideally as shown in the figure. Since torque is not generated if the applied voltage 53 is reduced to 0V, it may be changed as quickly as possible. In this switching, it is not always necessary to lower the applied voltage 53 to 0V. For example, even if the voltage is reduced to about 3/4, sufficient vibration compared to the conventional switching at 200V. An inhibitory effect is obtained.

Next, reduction is complete the applied voltage 53 in the arrow 53b, to secure the time a, the required excitation rate 52 at time t ₃ from at a further time b to the deceleration control as indicated by the arrow 53d from arrow 53c Increase again to a predetermined value. The speed of increase of the applied voltage 53 at this time may be set so as to return quickly, for example, in about 1 second, so that inappropriate vibration does not occur due to a sudden increase in torque accompanying a voltage change. It should be noted that either or both of the standby time a and the standby time b are substantially zero, and immediately after the reduction to the predetermined voltage is completed, the excitation speed 52 is changed as indicated by arrows 52a to 52b, and then the applied voltage 53 is immediately changed to the arrow 53d. You may comprise so that it may return like. The applied voltage 53 to be restored by the arrow 53d is higher than the voltage indicated by the arrow 53a. This is because the applied voltage 53 is set slightly lower than the rated value at a constant speed operation of 20000 rpm (settling state). It is.

Thereafter, performs deceleration control as in the conventional described techniques Figure 6, gradually decreases the applied voltage 53 as shown by the arrow 53f from the arrow 53e, the deceleration at time t ₅ the excitation rate 52 as zero at time t ₄ Control ends. As described above, according to the control described in FIG. 3, the applied voltage to the motor 4 is reduced to almost zero when the rotating magnetic field generated in the motor 4 is switched. The vibration generated when the difference, that is, the slip becomes small can be reduced, and an increase in noise can be prevented.

Next, changes in the rotation speed and excitation speed of the motor 4 and the voltage applied to the motor 4 when the motor 4 shifts from the deceleration operation to the constant speed operation will be described with reference to FIG. The horizontal and vertical axes in FIG. 4 are the same as those in FIG. 3 described above. At time t ₀ during deceleration lower excitation rate 62 than the rotation speed 61, a state where the negative slip occurs. At the time t ₁ when the rotational speed 61 reaches N ₂ ′ higher than the target rotational speed N ₂ by a predetermined value, the excitation voltage 62 maintains the predetermined negative slip while the applied voltage 63 is changed from the arrow 63b to the arrow 63c. Reduce rapidly. Here, the rate of reduction of the applied voltage 63 is preferably fast enough to prevent improper vibration due to a sudden change in braking torque accompanying a voltage drop, for example, in about 1 second.

After the applied voltage 63 has dropped to a predetermined value, as shown in 62b from an arrow 62a at time t ₂ has elapsed a predetermined time c, a predetermined positive slip relative to the excitation speed 62 speed 61 is generated values Increase to. Here, the speed at which the excitation speed 62 is increased may be increased to such an extent that inappropriate vibration due to the torque changing from negative to positive does not occur. In the control shown in FIG. 4, the applied voltage 63 is sufficiently reduced at the time of switching from the arrows 62a to 62b or within a predetermined time before and after the switching. In the present embodiment, the applied voltage 63 is reduced to 0 V at the time of switching the excitation speed 62 (time t ₂ ), so that the torque of the motor 4 is not generated, so that there is a significant risk of unnecessary vibrations. To reduce. The applied voltage 63 to be reduced when switching the excitation speed 62 is most preferably lowered to 0 V. However, if an effect of suppressing vibration can be obtained, for example, 3/4 or less of the arrow 63b, preferably It may be reduced to 1/2 or less, more preferably to almost zero. Further, the applied voltage 63 may be changed as quickly as possible. In the figure, the excitation speed 62 is changed after the waiting time c has elapsed after the decrease of the applied voltage 63 is completed, but this waiting time c need not be ensured.

Then, from time t ₂ to after a lapse waiting time d is again increased from an arrow 63d to a predetermined value required applied voltage 63 to constant speed operation as shown by arrow 63e. The speed of increase of the applied voltage 63 at this time is preferably as fast as, for example, about 1 second so that inappropriate vibration does not occur due to a rapid increase in torque accompanying a voltage change. Further After changed the end of the excitation rate 62 at time t _2, the may been increasing immediately applied voltage 63 without placing the waiting time d. Thereafter, the control device 7 detects the rotation speed 61 and performs feedback control to increase / decrease the excitation speed 62 or the applied voltage 63, thereby continuing the constant speed operation. Since the control method of the motor 4 for maintaining this constant speed operation may be controlled by a conventionally known technique, a description thereof is omitted here.

  Next, the control procedure of the motor 4 when changing the rotation speed will be described using the flowchart of FIG. The procedure shown in the flowchart can be realized by software control by a microcomputer (not shown) included in the calculation unit 8 executing a computer program.

When a power switch (not shown) of the centrifuge 1 is turned on, the calculation unit 8 receives an input of setting conditions for the centrifugal operation by the operator and an operation start input from the operation display unit 6 (see FIG. 1) (steps). 101). Then, the calculation part 8 starts the motor 4, rotates the rotor 2 at low speed, and reads the identification information recorded on the rotor 2, and identifies the specific information of the rotor 2 (step 102). Next, the calculation unit 8 sets a control condition based on the identified information of the rotor 2, accelerates the rotor 2 to the set rotational speed, and operates (sets) at a constant rotational speed (step 103). Next, the calculation unit 8 determines whether or not deceleration has been entered. Specifically, it is determined whether a predetermined operation time has expired in the settling state, or whether there is a stop operation from the operation display unit 6 by the operator (step 104). If none of the above applies, the operation waits until the condition is met, and if any of the conditions apply, in order to switch the excitation speed from a state higher than the rotational speed of the motor 4 to a lower state, the calculation unit 8 operates the inverter 10. To lower the voltage applied to the motor 4 (step 105). The control in step 105 is, for example, the control at time t _{1 in} FIG. 3, but the degree of voltage to be reduced is changed according to the type of the rotor 2 identified in step 102, for example, the voltage is reduced by 50%, the voltage May be configured to be finely controlled such that the voltage is reduced by 75% and the voltage is reduced to almost 0V.

  Next, the arithmetic unit 8 waits for a predetermined time with the voltage applied to the motor 4 lowered (for example, the standby time a in FIG. 3), and switches the excitation speed from a state higher than the rotational speed of the motor 4 to a lower state. (Steps 106 and 107). Note that the standby time a is not necessarily required, and it may not be necessary to ensure the standby time a in relation to the type of rotor to be mounted and the rotational speed, and may be set as appropriate.

  Next, the calculation unit 8 stands by for a predetermined time while maintaining the state where the voltage applied to the motor 4 is reduced (for example, the standby time b in FIG. 3), and increases the voltage applied to the motor 4 to Feedback control is performed so that the applied voltage conforms to the deceleration control (steps 108 and 109). Note that the standby time b is not necessarily required in the same manner as the standby time a, and it may not be necessary to secure the standby time b depending on the type of rotor to be mounted and the rotational speed. good. Thus, predetermined deceleration control is performed (step 110), and the motor 4 is stopped. Since the subsequent control is the same as a known control in a centrifuge conventionally used, description thereof is omitted here.

  By the control based on the above embodiment, when the rotational speed (excitation speed) of the rotating magnetic field supplied to the motor by the inverter changes from a higher state to a lower state than the motor rotational speed, or the motor rotational speed. When changing from a lower state to a higher state, the output voltage of the inverter is reduced at a predetermined ratio with respect to the output voltage before the start of the change, so slippage is positive and negative in the centrifuge motor control. It was possible to greatly suppress the generation of vibration during the transitional period.

  As mentioned above, although this invention was demonstrated based on the Example, this invention is not limited to the above-mentioned Example, A various change is possible within the range which does not deviate from the meaning. For example, in the above-described embodiment, an example of the transition from the constant speed operation to the deceleration control and the transition from the deceleration control to the constant speed operation is shown, but the present invention is not only related to this embodiment, and the acceleration control It can be implemented when the slip changes between positive and negative, such as deceleration control or transition from deceleration control to acceleration control. In the above-described embodiment, the description has been given on the assumption that the motor has two poles. However, even if the motor has four or more poles, the same effect can be obtained by increasing the excitation speed by 2 / P times. The application of the present invention is possible.

DESCRIPTION OF SYMBOLS 1 Centrifuge 2 Rotor 3 Door 4 Motor 5 Rotary chamber 6 Operation display part 7 Control apparatus 8 Arithmetic part 9 Rectifier 10 Inverter 11 Smoothing capacitor 12 Rotation sensor 13 Chamber 14 Shaft case 15 Temperature sensor 16 Shaft 17 Crown 18 Cooling device 18a Cooling Piping 20 Commercial power supply 51, 61 Rotational speed 52, 62 Excitation speed 53, 63 Applied voltage 251, 261 Rotational speed 252, 262 Excitation speed 253, 263 Applied voltage

Claims (8)

In a centrifuge having a rotor that holds a sample, a motor that rotationally drives the rotor, a rotation sensor that detects a rotation speed of the rotor or the motor, and a control device that controls the rotation of the motor.
The motor is an induction motor, and the control device includes a variable voltage variable frequency type inverter by pulse width modulation,
When the motor decelerates, the rotational speed of the rotating magnetic field supplied to the motor by the inverter is switched from a higher state to a lower state than the motor rotational speed ,
Wherein the control device before performing the switching, the inverter reduces the output voltage than the voltage at the start of deceleration, and that the output voltage is the switching of the rotational speed of the rotating magnetic field while being reduced performed Centrifuge. In a centrifuge having a rotor that holds a sample, a motor that rotationally drives the rotor, a rotation sensor that detects a rotation speed of the rotor or the motor, and a control device that controls the rotation of the motor.
The motor is an induction motor, and the control device includes a variable voltage variable frequency type inverter by pulse width modulation,
At the time of transition from decelerating to constant speed operation of the motor, the rotational speed of the rotating magnetic field supplied to the motor by the inverter is switched from a lower state to a higher state than the rotational speed of the motor,
Before performing the switching, the control device reduces the output voltage of the inverter below a voltage at the time of rotation higher than a rotation speed of constant speed rotation by a predetermined rotation speed, and the output voltage is reduced in the state where the output voltage is reduced. A centrifuge characterized by switching the rotation speed of a rotating magnetic field. The reduced state is a voltage that is ½ or less of the voltage at the start of deceleration, or ½ or less of the voltage at the time of rotation higher by a predetermined number of rotations than the number of rotations of the constant speed rotation. The centrifuge according to claim 1 or 2 , wherein   The centrifuge according to claim 3, wherein the reduced state is substantially zero voltage. Before at the time of switching the rotational speed of the Machinery rolling magnetic field, according to claims 1, characterized in that to maintain the reduced state of the inverter output voltage over a predetermined time before side and rear side in any one of the 4 Centrifuge.   The centrifuge according to any one of claims 1 to 5, wherein the inverter adjusts a voltage applied to the motor when the slip becomes small by pulse width modulation.   The centrifuge according to claim 6, wherein the control device calculates a slip from a difference between a rotation speed obtained from the rotation sensor and an excitation speed by the inverter, and controls an output voltage of the inverter. The rotor is removable;
4. The control device according to claim 1, wherein the control device identifies a type of the mounted rotor and determines a reduction ratio of the output voltage of the inverter according to the identified type. 5. The centrifuge described.

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