JP2010269274A - Controller and control method of crusher - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a controller and a control method of a crusher capable of stably increasing treatment efficiency even while avoiding an increase in abnormal load torque that is applied to a crusher rotor. <P>SOLUTION: The controller of the crusher including a crushing treatment section that crushes a crushed matter with the rotation of the crushing rotor where a rotary blade is fixed and an induction motor that drives the crushing rotor through a transmission mechanism, wherein an inverter circuit that drives the induction motor and a frequency control section that shifts the output frequency of the inverter circuit based on a load level of the induction motor from a first frequency f1 to a second frequency f2 different from the first frequency are provided, and the frequency control section shifts the output frequency with hysteresis characteristics so as to allow a first load level τ1 to shift the frequency from the first frequency f1 to the second frequency f2 to be different from a second load level τ2 to shift the frequency from the second frequency f2 to the first frequency f1, is provided. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a control device and a control method for a crushing device.

  The crushing device includes a crushing processing unit that crushes an object to be crushed by rotation of a crushing rotor to which a rotary blade is fixed, and an electric motor is drivingly connected to the crushing rotor via a speed change mechanism.

  With such a crushing device, various types of waste such as waste plastics, cut pieces of cloth, used clothes, magazines, etc. are crushed, and the crushed waste is recycled as raw material for RPF (Refuse Paper & Plastic Fuel). Used as a fuel for combustion equipment.

  Conventionally, the crushing device control device controls the frequency of the power supply applied to the field winding of the electric motor to a constant level, and detects abnormally high load on the crushing rotor. As a fail-safe treatment, the crushing rotor was driven in reverse after being stopped.

  However, the load applied to the crushing rotor varies depending on the composition and amount of the material to be crushed by the crushing processing unit. There is a problem that not only the power consumption increases and power consumption increases, but also the processing efficiency decreases.

  Furthermore, when an abnormally high load is applied to the crushing rotor and the fail-safe process is executed, the crushing process is stopped during that period, so that the processing efficiency is greatly reduced.

  Therefore, Patent Document 1 proposes a control device that reduces the rotational speed by controlling the drive frequency of the electric motor to about 50% when the load torque of the crushing rotor exceeds a preset steady torque.

JP 2008-284527 A

  However, the load torque applied to the crushing rotor fluctuates dynamically, and even if it instantaneously exceeds the steady torque, it often returns quickly thereafter.When the steady torque is exceeded, the drive frequency immediately applied to the motor is increased. On the other hand, there is a problem in that the processing efficiency is lowered when it is lowered.

  In addition, even if the drive frequency applied to the electric motor is frequently changed in response to fluctuations in the load torque, the crushing rotor having a large inertia may not respond quickly and there is a problem that the control efficiency is not good.

  Furthermore, depending on the composition and amount of the material to be crushed by the crushing processing unit, the fluctuation characteristics of the load torque applied to the crushing rotor are different, and if the steady torque is uniformly set, flexibility is lacking. When the composition and amount of the material to be crushed are known in advance, it is possible to set a steady torque that varies depending on the composition and amount of the material to be crushed, but generally there are various types of materials to be crushed. It is mixed and it is difficult to respond realistically.

  In view of the above-described problems, the present invention provides a control apparatus and a control method for a crushing apparatus that can stably increase the processing efficiency while avoiding an abnormal increase in load torque applied to the crushing rotor. In the point.

  In order to achieve the above-mentioned object, the first characteristic configuration of the control device for the crushing device according to the present invention is as described in claim 1 of the claims, by rotating the crushing rotor to which the rotary blade is fixed. It is a control device of a crushing device equipped with a crushing processing unit for crushing crushed material and an electric motor for driving a crushing rotor, an inverter circuit for driving the electric motor, and an output frequency of the inverter circuit based on the load level of the electric motor, A frequency control unit that switches from the first frequency to a second frequency that is different from the first frequency, and the frequency control unit includes a first load level for switching from the first frequency to the second frequency, and a second frequency from the second frequency. The point is that switching is performed with a hysteresis characteristic so that the second load level to be switched to one frequency is different.

  When the electric motor is driven at the first frequency and the load torque of the crushing rotor reaches the first load level, the frequency controller switches to the second frequency and drives the electric motor at the second frequency. When the load torque of the crushing rotor reaches a second load level different from the first load level, the drive is switched to the first frequency.

  In other words, even when the load applied to the crushing rotor frequently fluctuates depending on the composition and amount of the material to be crushed by the crushing processing unit, switching between the first frequency and the second frequency has hysteresis characteristics. Therefore, even if there are some fluctuations in the load, it can be driven at a predetermined frequency, and while avoiding a decrease in control efficiency such that the drive frequency is frequently switched, it can be stably crushed Efficiency can be improved.

  As described in claim 2, the second characteristic configuration is the first load level for switching from the first frequency to the second frequency lower than the first frequency in addition to the first characteristic configuration described above. Thus, the second load level for switching from the second frequency to the first frequency is switched with a hysteresis characteristic set to be low.

  For example, an object to be crushed containing a large amount of high bulk density has an average load, but the crushing process is continued at a high rotational speed until the first load level set as the upper limit is reached. When the load level is reached, a stable crushing process is continued by switching to the second frequency and reducing the rotation speed of the crushing rotor.

  Then, for example, when the average load torque is reduced by changing to an object to be crushed containing a lot of low bulk density and reaches a second load level set lower than the first load level, the first frequency is reached. By switching and increasing the rotation speed of the crushing rotor, the crushing process can be continued efficiently.

  In the third feature configuration, as described in claim 3, in addition to the second feature configuration described above, the frequency control unit switches to the second frequency immediately when the load level rises above the first load level, When the level falls below the second load level, the state is continued for a predetermined time and then switched to the first frequency.

  If the load level rises above the first load level, the probability of reaching an abnormally high load level that requires the crushing rotor to be stopped or reversed is increased, so the stable crushing process continues immediately by switching to the second frequency. To do. And even if the load level falls below the second load level, it does not immediately switch to the first frequency, but waits for the state to continue for a predetermined time, that is, after the load level is stably lowered to the first frequency. Switch. Therefore, frequent switching between the first frequency and the second frequency is effectively avoided.

  In the fourth feature configuration, as described in claim 4, in addition to the second feature configuration described above, the frequency control unit switches to the second frequency immediately when the load level rises above the first load level, When the load level falls below the second load level after a lapse of time, the first frequency is switched.

  If the load level rises above the first load level, the probability of reaching an abnormally high load level that requires the crushing rotor to be stopped or reversed is increased, so the stable crushing process continues immediately by switching to the second frequency. To do. And if it detects that the load level fell from the 2nd load level after continuing driving by the 2nd frequency for a predetermined time, without switching to the 1st frequency immediately even if a load level falls from the 2nd load level. Switch to the first frequency. Therefore, frequent switching between the first frequency and the second frequency is effectively avoided.

  In the fifth feature configuration, as described in claim 5, in addition to any of the second to fourth feature configurations described above, a plurality of sets of first frequency and second frequency are set. A switch for selecting the set is provided, and the frequency control unit corresponds to the first frequency and the second frequency corresponding to the set selected by the switch, and the first for switching from the first frequency to the second frequency. The point is that the load level and the second load level to be switched from the second frequency to the first frequency are switched with a hysteresis characteristic so as to be different.

  Depending on the composition and amount of the material to be crushed in the crushing processing unit, the fluctuation characteristics of the load applied to the crushing rotor are different, and the processing efficiency also varies, but if the first frequency and the second frequency are fixed, There is no guarantee that processing efficiency will be appropriate. Therefore, by setting multiple sets of the first frequency and the second frequency, and switching to an appropriate frequency combination with a switch, the degree of freedom for obtaining an appropriate treatment efficiency is improved corresponding to the composition and amount of the material to be crushed. To do.

  In the sixth feature configuration, as described in claim 6, in addition to any of the second to fourth feature configurations described above, a plurality of first load levels and second load levels are set. A switch for selecting one of the sets is provided, and the frequency control unit switches from the first frequency to the second frequency at the first load level and the second load level corresponding to the set selected by the switch, or The point is to switch from the second frequency to the first frequency.

  As described above, the fluctuation characteristics of the load applied to the crushing rotor vary depending on the composition and amount of the material to be crushed by the crushing processing unit, and the processing efficiency also varies, but the first load level and the second load level are fixed. Therefore, there is no guarantee that the processing efficiency is appropriate. Therefore, by setting multiple sets of the first load level and the second load level and switching to the appropriate load level combination with a switch, it is possible to obtain an appropriate treatment efficiency corresponding to the composition and amount of the object to be crushed. The degree is improved.

  In the seventh feature configuration, in addition to any one of the second to sixth feature configurations described above, the load level is an average value of instantaneous load values, and the first load The level is set to a different value depending on the fluctuation range of the instantaneous load value.

  The load applied to the crushing rotor frequently varies depending on the composition and amount of the material to be crushed by the crushing unit. If the drive frequency is switched with such an instantaneous load value, the processing efficiency may be reduced. Therefore, it is possible to avoid a decrease in processing efficiency by using the load level as an average value of instantaneous load values and dulling fluctuations in the load, which is an index for switching the drive frequency. At this time, by setting the first load level to a different value according to the fluctuation range of the instantaneous load value, it is possible to avoid the occurrence of an abnormal high load level that requires the crushing rotor to be stopped or reversely controlled. be able to. For example, the first load level when the fluctuation range is large is adaptively set to be smaller than the first load level when the fluctuation range of the instantaneous load value is small.

  In the eighth feature configuration, in addition to any one of the second to seventh feature configurations described above, the load level is an average value of instantaneous load values, and the first frequency Is set to a different value depending on the fluctuation range of the instantaneous load value.

  Similar to the fourth feature configuration, the load level is an average value of the instantaneous load values, and the decrease in processing efficiency is avoided by dulling the fluctuation of the load, which is an index for switching the drive frequency. By setting the first frequency to a different value according to the fluctuation range of the instantaneous load value, it is possible to avoid the occurrence of an abnormally high load level that requires the crushing rotor to be stopped or reversely controlled. . For example, the first frequency when the fluctuation range is large is adaptively set to be smaller than the first frequency when the fluctuation range of the instantaneous load value is small.

  In the ninth feature configuration, in addition to the seventh or eighth feature configuration described above, the crushing device is driven back and forth with respect to the crushing processing unit, and the object to be crushed is A pusher mechanism for pressing the crushing processing unit is provided, and the load level is set as an average value of instantaneous load values within a predetermined time when the pusher mechanism is advanced to the crushing processing unit.

  The crushing process proceeds efficiently in a state where the pusher mechanism is advanced and the object to be crushed is pressed by the crushing part, but the pusher mechanism is retreated and the pressing state of the object to be crushed is in the crushing part. Since the crushing process does not proceed so efficiently in the state of being eliminated, the load applied to the crushing rotor is different for each. Therefore, by adopting the average value of the instantaneous load values at the time of advance operation in which the load applied to the crushing rotor is large as the load level, it is possible to perform appropriate control for increasing the efficiency of the crushing process.

  In the tenth feature configuration, as described in claim 10, in addition to any of the second to ninth feature configurations described above, the output frequency range of the inverter circuit is divided into a plurality of regions. The first frequency and the second frequency are set.

  Since the load torque applied to the crushing rotor varies depending on the composition and amount of the material to be crushed by the crushing unit, the first frequency and the second frequency in each of the output frequencies of the inverter circuit divided into a plurality of regions. By setting the frequency, an efficient crushing process can be performed under appropriate conditions according to the composition and amount of the object to be crushed.

  According to the eleventh characteristic configuration, as described in claim 11, in addition to any of the first to tenth characteristic configurations described above, the eleventh characteristic configuration is a processing amount of the object to be crushed by the crushing processing unit. On the basis of this, there is a learning unit that sets the first frequency or the second frequency so that the processing amount increases and / or the power consumption decreases.

  The processing amount of the object to be crushed by the crushing processing unit is learned by the learning unit, which is appropriate for the composition and amount of the set object to be crushed, that is, the processing amount increases or the current consumption decreases. Such a drive frequency is automatically set.

  According to the first characteristic configuration of the control method of the crushing apparatus according to the present invention, a crushing processing unit that crushes an object to be crushed by rotation of a crushing rotor with a rotating blade fixed thereto, A control method for a crushing device including an electric motor to be driven and an inverter circuit for driving the electric motor, wherein the output frequency of the inverter circuit is different from the first frequency to the second frequency based on the load level of the electric motor. The first load level for switching to the second load level and the second load level for switching from the second frequency to the first frequency are switched with a hysteresis characteristic.

  As described in claim 13, the second characteristic configuration includes, in addition to the control method according to the first characteristic configuration, a second load level that is switched from the first frequency to a second frequency lower than the first frequency. The second load level for switching from the frequency to the first frequency is to switch with a hysteresis characteristic set to be low.

  As described above, according to the present invention, there is provided a control device and a control method for a crushing device capable of stably increasing the processing efficiency while avoiding an abnormal increase in load torque applied to the crushing rotor. I was able to do it.

Schematic diagram of crusher Side view of crushing device Top view of crusher Illustration of hydraulic circuit (A) is explanatory drawing of a system control apparatus, (b) is explanatory drawing of a motor control apparatus. Flow chart for starting control of crusher Flow chart of crushing device stop control (A) is explanatory drawing of the frequency characteristic of an induction motor, (b) is explanatory drawing which shows the relationship between the slip of an induction motor, and a torque. Explanatory drawing of the frequency switching control performed by the control apparatus of this invention Flowchart of frequency switching control executed by the control device of the present invention Explanatory drawing of the frequency switching control which shows another embodiment and is performed by the control apparatus of this invention Explanatory drawing of the frequency switching control which shows another embodiment and is performed by the control apparatus of this invention

Hereinafter, preferred embodiments of the crushing apparatus according to the present invention will be described.
As shown in FIGS. 1 to 3, the uniaxial shearing type crushing device 1 includes a receiving hopper 2 that inputs waste plastic selected from electrical appliances and building waste materials, waste paper, used clothes, and the like. A crushing processing unit 10 that crushes the material to be crushed charged into the hopper 2 and a pusher mechanism that presses the material to be crushed from the horizontal direction toward the crushing processing unit 10. The operation is controlled by the device 100.

  The pusher mechanism is configured such that an arm 3a connected to a piston of a hydraulic cylinder 3b that is driven forward and backward by hydraulic oil supplied from a hydraulic pump 52 provided in a hydraulic circuit 60 described later is connected to the rear end of the pusher pusher 3. The board 4 is driven forward and backward in the horizontal direction to press the object to be crushed toward the crushing processing unit 10.

  The crushing processing unit 10 is disposed below the receiving hopper 2 and has a tip v-shaped rotary blade 6 fixed to a groove formed in the circumferential direction on the peripheral surface of the crushing rotor 5 that rotates around a predetermined axis. The crushing rotor 5 includes a tip v-shaped fixed blade 7 that is opposed to the crushing rotor 5 along the direction of the rotation axis 5c and meshes with the rotary blade 6 to shear and crush the object to be crushed.

  A large number of v-shaped grooves 5v that are parallel to each other at a predetermined pitch are formed in the peripheral portion of the crushing rotor 5, and the blade bodies 6a are bolted to the plurality of mounting seats 6b formed in the grooves 5v. It is fastened. Each rotary blade 6 is arranged in a zigzag shape when those provided in adjacent v-shaped grooves 5v are connected to each other. In the fixed blade 7, a v-shaped blade body 7 a at the tip is fastened with a bolt to a mounting seat 7 b provided at the end of the base 4 along the axial direction of the crushing rotor 5.

  In the lower part of the crushing processing unit 10, a screen mechanism 8 for selectively passing the object to be crushed to a predetermined size or less by the rotary blade 6 and the fixed blade 7, and a discharge for receiving the object to be crushed that has passed the screen mechanism 8. A hopper 9 is provided.

  The screen mechanism 8 is formed of a punching metal that is curved in an arc shape along the rotation trajectory of the rotary blade 6 and has a large number of apertures. The object to be crushed smaller than the opening is dropped from the opening and accommodated in the discharge hopper 9, and the material not passing through the opening is crushed again by the rotary blade 6 and the fixed blade 7.

  An electric motor M as a driving machine is fixed to a gantry below the crushing device 1, and a speed reduction mechanism 30 as a speed change mechanism is fixed to a mounting gantry 12 a as an example of a support body assembled to one side 11 a of the main body frame 11. . The pulley 13 attached to the output shaft of the motor M and the pulley 15 attached to the input shaft 31 of the speed reduction mechanism 30 are connected by the v-belt 14, and the power of the motor M is shifted to a predetermined rotational speed by the speed reduction mechanism 30. Then, it is configured to be output from the output shaft 37 and transmitted to the rotating shaft 5 c of the crushing rotor 5.

  Note that the output shaft of the motor M and the input shaft 31 of the speed reduction mechanism 30 may be coupled by a coupling instead of the v-belt 14 via the pulleys 13 and 15.

  Below, the hydraulic circuit 60 and the system control apparatus 100 of the crushing apparatus 1 are demonstrated. As shown in FIG. 4, the hydraulic circuit 60 of the crushing apparatus 1 includes a hydraulic pump 52 that supplies hydraulic oil at a predetermined flow rate, a pressure adjusting mechanism 57 that adjusts the pressure of hydraulic oil output from the hydraulic pump 52, and a hydraulic pump. A supply pipe 51 that supplies hydraulic oil supplied from 52 to the hydraulic cylinder 3 b of the pusher pusher 3, and a switching valve 53 that is installed in the supply pipe 51 and switches between forward and backward drive of the pusher pusher 3. A sequence valve 54 is provided upstream of the switching valve 53, and a relief valve 63 is provided downstream of the switching valve 53.

  The relief valve 63 opens when a large load is applied to the pusher pusher 3 due to, for example, a large foreign matter being introduced into the crushing processing unit 10 while the hydraulic cylinder 3b is moving forward, and the pressure in the supply pipe 51 exceeds a predetermined pressure. The hydraulic oil supplied from the hydraulic pump 52 is allowed to escape to the oil tank 59 to protect the hydraulic circuit 60.

  The hydraulic pump 52 is an electromagnetic two-pressure two-volume control type piston pump, and controls the pressure regulating mechanism 57 according to the operation of the switching valve 53 to discharge a low-pressure large flow rate and a high-pressure small flow rate. The pusher 3 is configured to drive forward and backward.

  As shown in FIG. 5A, the system control device 100 of the crushing device 1 includes signals of the start switch S1 and the stop switch S2, and the forward switch S3 and the reverse switch S4 provided in the hydraulic cylinder 3b of the pusher pusher 3. When the signal is input, the motor M is controlled to start and stop via the motor control device 200, which is a control device according to the present invention, the start and stop control is performed to the hydraulic pump 52 that supplies hydraulic oil to the supply pipe 51, and the hydraulic pump 52 The pressure regulating mechanism 57 is controlled, and the switching valve 53 for forward and backward control of the pusher pusher 3 is controlled.

  The system control device 100 may be provided inside the crushing device 1 or inside a control panel or the like outside the crushing device 1.

  When the crushing apparatus 1 is activated, based on the input of the activation switch S1, the electric motor M is activated after the hydraulic pump 52 is activated, the switching valve 53 is controlled, and the push-pusher 3 is started to move forward and backward.

  At the time of stoppage, the switching valve 53 is controlled to stop the operation of the pusher pusher 3 and the electric motor M is stopped.

  The starting control of the crushing apparatus 1 will be described based on the flowchart shown in FIG. When the start switch S1 is turned on (SA1), the system control device 100 starts the hydraulic pump 52 to supply hydraulic oil to the hydraulic circuit (SA2).

  When the pressure in the supply pipe 51 reaches a predetermined pressure (SA4), the electric motor M is started to rotate the crushing rotor 5 (SA5).

  When the crushing rotor 5 is rotated by the power of the electric motor M, the switching valve 53 is controlled to drive the push-in pusher 3 forward (SA6). Here, if the pressure in the supply pipe is a predetermined pressure (YES in SA7), the forward pusher 3 continues to be driven until the forward limit switch S3 is turned on (NO in SA8).

  When the forward limit switch S3 is turned on (YES in SA8), the switching valve 53 is controlled to drive the pusher pusher 3 backward (SA9). Here, if the pressure in the supply pipe is a predetermined pressure (YES in SA10), the pushing pusher 3 continues to be driven backward until the backward limit switch S3 is turned on (NO in SA11). When the reverse limit switch S3 is turned ON (YES in SA11), the switching valve 53 is controlled to drive the pusher pusher 3 forward again (SA6).

  If the pressure in the supply pipe is not a predetermined pressure in steps SA4, SA7, and SA10 described above, the motor M is stopped (SA12), the hydraulic pump 52 is stopped (SA13), and an error has been reported ( SA14), the start control is terminated.

  Next, stop control of the crushing apparatus 1 will be described based on the flowchart shown in FIG. When the stop switch S2 is turned on (YES in SB1), the system control device 100 controls the switching valve 53 to stop the driving of the pusher pusher 3 (SB2), and the electric motor M is stopped to stop the rotation of the crushing rotor 5. Stop (SB3), stop the hydraulic pump 52 that supplies hydraulic oil to the hydraulic circuit (SB4), and terminate the stop control.

Next, the motor control device 200 will be described.
As shown in FIG. 5B, the motor control device 200 is applied to a rectifier circuit 220, a capacitor, an inverter circuit 230, a frequency control unit 240, and an electric motor M connected to a commercial power supply 210 of 400V, 60 Hz. A current sensor 250 for monitoring the load torque is provided.

  The voltage converted into direct current by the rectifier circuit 220 and the capacitor is converted into an alternating voltage of a predetermined frequency by the inverter circuit 230 and applied to the field coil of the electric motor M. The motor M is a saddle type induction motor, and the rotor is rotationally driven by a rotating magnetic field generated by a field coil.

  The inverter circuit 230 is a V / f control type inverter that variably adjusts the frequency and voltage so that the ratio of the frequency and voltage applied to the field coil is constant based on a control command from the frequency control unit 240. Circuit.

As shown in FIG. 8A, when the frequency applied to the electric motor M is increased or decreased, the synchronous speed N ₀ changes accordingly, but the starting torque, stopping torque, and rated torque of the electric motor M change. In addition, the slip S _{0 with} respect to the synchronous speed N ₀ when driven at the rated torque also shows a substantially constant characteristic.

As shown in FIG. 8B, when the load torque of the electric motor M driven at a certain frequency increases from the point A to the point B, the slip increases from S ₁ to S ₂ and the torque τ is increased. At the same time, the current increases and the copper loss on the secondary side increases. In such a case, when the drive frequency is lowered, the torque corresponding to the load torque is reduced while the rotational speed is lowered by the V / f control and the current is lowered to suppress the increase in the secondary side copper loss. Can be secured.

  Note that when the drive frequency is lowered, the impedance of the field winding of the electric motor M is reduced and the field winding may be burned out due to excessive current. The current is controlled to decrease by decreasing the voltage in proportion.

  As shown in FIG. 9A, the frequency control unit 240 has a first load level τ1 for switching from the first frequency f1 to the second frequency f2, and a second load for switching from the second frequency f2 to the first frequency f1. Switching is performed with hysteresis characteristics so that the level τ2 is different. In the present embodiment, the second load level τ2 is set lower than the first load level τ1.

  When receiving the activation command from the system control unit 100, the frequency control unit 240 starts the electric motor M at the first frequency f1, rotationally drives the crushing rotor, and executes the crushing process.

  The frequency control unit 240 receives a state signal indicating the operating state of the pusher mechanism from the system control unit 100, and inputs an instantaneous current value detected by the current sensor 250 at a predetermined interval while the pusher mechanism is operating. Then, the value is stored in the built-in memory, and the moving average value of the instantaneous current value for a predetermined number of times (hereinafter simply referred to as “average value”) is calculated as the load torque applied to the motor M. That is, the load level applied to the electric motor M is calculated as an average value of instantaneous load values at the time of advance operation to the crushing processing unit of the pusher mechanism.

  It is also possible to use a sensor other than the current sensor as a sensor for detecting the load level. For example, a torque meter or the like may be provided on the output shaft of the electric motor M, the rotating shaft of the crushing rotor, the output shaft of the speed change mechanism, or the like. By using a torque meter or the like, the load torque of the electric motor M can be accurately detected, and the load torque can be handled as a load level.

  When the motor M is being driven at the operating point P1, the frequency control unit 240 immediately switches to the second frequency f2 when the load level rises above the first load level τ1, and drives the motor M at the operating point P2, so that the load level is the first level. When the load level drops below the two load levels τ2, the state continues for a predetermined time, and then the frequency is switched to the first frequency f1.

  That is, if the load level rises above the first load level τ1 while driving the electric motor M at the operating point P1, the probability of reaching an abnormally high load level τfs that requires the crushing rotor to be stopped or reversed is increased. Therefore, the stable crushing process is continued by immediately switching to the second frequency f2.

  Even if the load level falls below the second load level τ2, the first frequency f1 is not immediately switched, but the state continues for a predetermined time, that is, the first time after the load level is stably lowered. Switch to frequency f1. As a result, frequent switching between the first frequency f1 and the second frequency f2 is effectively avoided.

  Even when the electric motor M is driven at any frequency, when the load level reaches the high load level τfs, the electric motor M is immediately stopped and the reverse rotation is promptly performed. The driving frequency during reverse driving, that is, the fail safe frequency is set to a value lower than the second frequency.

  In other words, even if the load torque applied to the crushing rotor frequently fluctuates depending on the composition and amount of the material to be crushed by the crushing processing unit, switching between the first frequency and the second frequency has hysteresis characteristics. Because it is carried out, it will be driven at a constant frequency even if there is some fluctuation in the load torque, and it will be stable while avoiding a decrease in control efficiency such that the drive frequency is frequently switched The crushing efficiency can be improved.

  For example, an object to be crushed containing a large amount of high bulk density has an average load torque, but until the first load level τ1 set as the upper limit value is reached, the slip is somewhat increased and the copper on the secondary side is increased. Even if the loss increases, an efficient crushing process is continued with high rotation and high torque, and when the first load level τ1 is reached, the frequency is switched to the second frequency f2 to reduce the rotation speed of the crushing rotor. The crushing process is continued.

  The rated torque for the second frequency is the same value as the rated torque for the first frequency, but the secondary side copper loss is reduced because the current is reduced by the V / f control method.

  After that, for example, when the average load torque is reduced by changing to an object to be crushed containing a large amount of low bulk density and reaches a second load level τ2 set lower than the first load level τ1, By switching to the frequency f1 and increasing the rotation speed of the crushing rotor, the crushing process can be continued efficiently. The first load level is set to a level lower than an abnormally high load level that requires the crushing rotor to be stopped or reversely controlled.

  By performing such control, the processing efficiency can be stably increased while avoiding an abnormal increase in load torque applied to the crushing rotor without causing an increase in power consumption.

  The values of the first frequency f1 and the second frequency f2 are not particularly limited. For example, the value of the first frequency f1 is 120% to 160% of the power supply frequency, and the value of the second frequency f2 is the power supply frequency. It is preferable to set the value to 90% to 110%.

  The values of the first load level τ1, the second load level τ2, and the like are not particularly limited. For example, the value of the second load level τ2 is a value before and after the rated torque, and the value of the first load level τ1. Is preferably set to a value around 150% of the rated torque, and a value of the high load level τfs that requires reverse rotation control is set to a value around 200% of the rated torque.

  For example, a crushing apparatus having a crushing rotor having a diameter of about 600 mm incorporates a rated current 270A, 10-pole induction motor M, crushing waste paper with a constant frequency set to 60 Hz, and a first frequency f1 Compared with the case where waste paper is crushed by setting 87 Hz and the second frequency f2 to 60 Hz, the former is processed at 3.41 tons per hour at an average current of 215 amps, and the average current for processing unit weight is In contrast to the 63 A / t / h, the latter can process 5.49 tons per hour at an average current of 240 amps, and the average current for processing unit weight is 43 A / t / h. It has been found that the average current for processing unit weight is reduced while increasing the throughput per hour.

  Hereinafter, the operation of the frequency control unit 240 will be described based on the flowchart shown in FIG.

  When receiving the start command from the system control unit 100 (SC1), the frequency control unit 240 sets the first frequency f1 (SC2) and starts the motor M (SC3).

  When the pusher mechanism is moving forward, that is, moving forward (SC4), the instantaneous load current detected by the current sensor 250 at a predetermined interval is input and stored in the memory (SC5). An average value of the instantaneous load currents thus calculated is calculated and set as a load level (SC6).

  For example, it is possible to calculate an average value of dozens of times by inputting ten or more times at intervals of several seconds. Alternatively, the average value may be calculated when the forward operation by the pusher mechanism is completed a predetermined number of times while the instantaneous load current is input at a predetermined interval.

  Meanwhile, if the instantaneous load current shows an abnormally high load level τfs (SC7), the motor M is stopped and then set to the fail-safe frequency (SC20), the motor M is driven in reverse (SC21), and the process proceeds to step SC11. .

  If the instantaneous load current is smaller than the abnormally high load level τfs (SC7), it is determined whether or not the motor M is being driven in reverse rotation. If the motor is being driven in reverse rotation (SC8), the reverse drive is continued until a predetermined time has elapsed. When the predetermined time has elapsed (SC17), the drive frequency of the motor M is set to the second frequency f2 and switched to normal rotation drive (SC19).

  If it is determined in step SC8 that the forward rotation drive is being performed, it is determined whether or not the load level is greater than the first load level τ1 (SC9), and if the load level is greater than the first load level τ1, The drive frequency is switched to the second frequency f2.

  If the load level is smaller than the first load level τ1 (SC9), if not driven at the second frequency f2, that is, if driving at the first frequency f1 (SC13), the state is maintained and step SC11 is performed. Proceed to

  When the load level is smaller than the first load level τ1 (SC9), when driven at the second frequency f2 (SC13), it is determined whether or not the load level is smaller than the second load level τ2 (SC14). If the load level is smaller than the second load level τ2, the drive frequency is switched to the second frequency f2 after maintaining the state for a predetermined time, for example, a few dozen seconds (SC15).

  The frequency control unit 240 indicates a control signal of the motor M, that is, a state signal indicating whether the motor M is driven at the first frequency f1, the second frequency f2, or the reverse drive at the fail-safe frequency. The system controller 100 is configured to receive the status signal and appropriately control the pusher mechanism.

  For example, when the reverse drive is performed at the fail-safe frequency, the advancement operation of the pusher mechanism is stopped or the reverse operation is performed.

  The above is the basic control mode of the control device according to the present invention. Below, the application of a basic control aspect is demonstrated.

  In the basic control mode, the frequency control unit switches to the second frequency immediately when the load level rises above the first load level, and when the load level falls below the second load level, the state continues for a predetermined time. However, the frequency control unit switches to the second frequency as soon as the load level rises above the first load level, and the first time when the load level falls below the second load level after a predetermined time has elapsed. You may control to switch to a frequency.

  Further, the frequency control unit switches to the second frequency as soon as the load level rises above the first load level, and assumes that the load level falls below the second load level after a lapse of a predetermined time. You may control to switch to.

  In the basic control mode, the case where the first load level is set to a fixed value has been described. However, the first load level τ1 may be controlled to change based on the operating state of the apparatus. For example, the load level may be set as an average value of instantaneous load values, and the first load level τ1 may be set to a different value depending on the fluctuation range of the instantaneous load value.

  As shown in FIG. 9B, when the frequency control unit 240 calculates the average value of the instantaneous load values that are the instantaneous current values detected by the current sensor 250, a plurality of instantaneous current values to be calculated are calculated. A fluctuation range that is a difference between the maximum value and the minimum value of the first load level is calculated. When the fluctuation range is smaller than a predetermined threshold, the first load level is set to τ11. When the fluctuation range is larger than the predetermined threshold, the first load level is calculated. Is set to τ12 smaller than τ11.

  When the fluctuation range of the instantaneous load value is large, there is a high possibility that the load level reaches the high load level τfs, and when the high load level τfs is reached, it is necessary to reversely drive the motor M, so the crushing processing efficiency decreases. To do.

  Therefore, when the fluctuation range of the instantaneous load value is large, the first load level is set to be low, and the crushing device is stably operated at the operating point P22 by switching to the second frequency f2 at an early stage. When the width is small, the possibility that the load level reaches the high load level τfs is reduced. Therefore, the crushing apparatus is efficiently operated at the operating point P21 by setting the first load level higher.

  The first load level is not limited to the levels of τ11 and τ12, but can be set to a plurality of levels of three or more levels, and the threshold value of the fluctuation range of the instantaneous load value for that purpose is also set as appropriate. Can do.

  Similarly, the second load level may be controlled to change based on the operating state of the apparatus. For example, the load level may be set as an average value of the instantaneous load value, and the second load level may be set to a different value depending on the fluctuation range of the instantaneous load value.

  Further, the first frequency f1 may be set to a different value depending on the fluctuation range of the instantaneous load value by the frequency control unit 240.

  As shown in FIG. 9C, when the frequency control unit 240 calculates the average value of the instantaneous load values that are the instantaneous current values detected by the current sensor 250, a plurality of instantaneous current values to be calculated are calculated. A fluctuation range which is a difference between the maximum value and the minimum value of the first frequency is calculated. When the fluctuation range is smaller than a predetermined threshold, the first frequency is set to f11, and when the fluctuation range is larger than the predetermined threshold, the first frequency is set to f11. The lower frequency f12 is set.

  When the fluctuation range of the instantaneous load value is large, there is a high possibility that the load level reaches the high load level τfs, and when the high load level τfs is reached, it is necessary to reversely drive the motor M, so the crushing processing efficiency decreases. To do.

  Therefore, when the fluctuation range of the instantaneous load value is large, the first frequency is set to a lower frequency f12 so that the fluctuation range of the instantaneous load value is small, and the crushing device is operated at the operating point P12. When the fluctuation range of the load value is small, the first frequency is set to a higher frequency f11, and the crushing apparatus is operated efficiently by operating the crushing apparatus at the operating point P11.

  If comprised in this way, when the fluctuation | variation range of an instantaneous load value changes with properties of a to-be-crushed object, it will become possible to perform a crushing process efficiently, reducing the probability of reaching high load level (tau) fs.

  Similarly, the frequency controller 240 may be configured to set the second frequency f2 to a different value depending on the fluctuation range of the instantaneous load value.

  Further, the load level is set as an average value of instantaneous load values, the first load level τ1 is set to a different value depending on the fluctuation range of the instantaneous load value, and the first frequency f1 is different depending on the fluctuation range of the instantaneous load value. You may comprise so that it may be set to.

  The load level is set as an average value of the instantaneous load values, the first load level τ1 and the second load level τ2 are set to different values depending on the fluctuation range of the instantaneous load value, and the first frequency f1 and the second frequency f2 are set. A different value may be set depending on the fluctuation range of the instantaneous load value.

  In any case, the frequency control unit 240 controls the drive frequency or the load level with a fixed value set in advance, or sets it to a different value depending on the fluctuation range of the instantaneous load value. It is also possible to provide a switch for selecting whether to input a selection signal from the switch to the frequency control unit 240.

  FIG. 11A shows a case where the first frequency is set to two levels f1 and f2 and the first load level is set to three levels τ1, τ2, and τ3 depending on the fluctuation range of the instantaneous load value. ing. Here, the second frequency is set to f3, and the second load level is set to τ4.

  The combinations of the operating point at the first frequency and the operating point at the second frequency are (P1, P5), (P1, P4), (P1, P3), (P2, P5), (P2, P4), ( There are 6 patterns of P2 and P3). By selecting which pattern to use based on the fluctuation range of the instantaneous load value, the crushing process can be performed with an appropriate pattern according to the properties of the object to be crushed. it can. Specifically, the pattern is selected so that the second frequency is greatly decreased as the fluctuation range of the instantaneous load value is larger.

  That is, a plurality of sets of the first frequency f1 and the second frequency f2 are set, and a manually operable switch for selecting any one of the sets is provided, and the frequency control unit 240 corresponds to the set selected by the switch. Provide hysteresis characteristics so that the first load level for switching from the first frequency to the second frequency and the second load level for switching from the second frequency to the first frequency are different for one frequency and the second frequency. It may be configured to control so as to switch.

  As an application of such control, the frequency of the motor M is set to three levels f1, f2, and f3, the load level is set to four levels τ1, τ2, τ3, and τ4, and the operating point is set to 8 from P1 to P8. By setting the point, the combinations of the operating point at the first frequency and the operating point at the second frequency are (P1, P8), (P1, P7), (P1, P6), (P1, P5), Any of 9 patterns (P1, P4), (P1, P3), (P2, P5), (P2, P4), (P2, P3) is used based on the fluctuation range of the instantaneous load value. By selecting whether or not to perform, the crushing process can be performed in an appropriate pattern according to the properties of the object to be crushed.

  For example, for crushed materials with extremely large load fluctuations, switching at the operating point (P1, P3) reduces the probability of reaching the abnormal load level τfs, improves crushing efficiency, and crushes with relatively small load fluctuations. By switching at the operating point (P2, P5), the product can be crushed at the operating point P2 as much as possible to improve the processing efficiency.

  Furthermore, the output frequency of the inverter circuit 230 can be divided into a plurality of regions, and the first frequency and the second frequency can be set in each region.

  FIG. 11B shows such a case, and the output frequency range of the inverter circuit 230 is divided into upper and lower sides with the frequency f2 as a boundary, and the first frequency f1, the second frequency f2, and the first load level are divided in the upper region. In this example, τ3 and the second load level τ4 are set, and in the lower region, the first frequency f2, the second frequency f3, the first load level τ1, and the second load level τ2 are set.

  The upper region is operated at any of the operating points (P1, P2), and the lower region is operated at any of the operating points (P3, P4). The frequency control unit 240 controls the inverter circuit 230 by selecting at which operating point the motor M is driven based on the fluctuation range of the instantaneous load value that is the instantaneous current value detected by the current sensor 250. is there.

  For example, when crushing a paper bundle or cloth that has a relatively large load torque, even if the crushing rotor is rotated at a high speed, the cloth is rotated with the crushing rotor in the crushing processing section and passes through the screen mechanism 8. Therefore, a phenomenon that the processing efficiency is reduced occurs. When such an object to be crushed is processed at the operating points (P3, P4), the crushing efficiency is improved.

  On the contrary, when crushing hard resins with relatively small load torque, it is preferable to treat at the operating point (P1, P2) because crushing efficiency is improved by rotating the crushing rotor at a high speed.

  When a plurality of combinations of operating points are set as shown in FIGS. 11A and 11B, a switch for switching at which operating point is provided is provided, and the signal of the switch is subjected to frequency control. An operating point can be selected by inputting to the unit 240.

  As shown in FIG. 12 (a), as an example of setting a plurality of first and second frequencies, the frequency control unit 240 sets the load levels τ1 to τ2 between the frequencies f1 and f2. It may be controlled to change in steps according to the load level.

  Furthermore, as shown in FIG. 12B, as an example of setting a plurality of sets of the first frequency and the second frequency, the frequency control unit 240 sets the load levels τ1 to τ2 between the frequencies f1 and f2. It may be controlled so as to change continuously according to the load level. In this case, as the load level rises above τ2, the frequency is decreased according to the upwardly convex curve in the figure, and after the load level reaches τ1, the load level decreases in the figure, It is preferable to increase the frequency according to a downwardly convex curve.

  If the load level decreases in the middle of decreasing the frequency according to the upwardly convex curve, the frequency is increased according to the upwardly convex curve, and if the load level increases in the middle of increasing the frequency according to the downwardly convex curve, The frequency may be lowered according to a convex curve. In this case, the load level that changes the frequency between the frequencies f1 and f2 can be controlled with hysteresis.

  Also, if the load level decreases in the middle of decreasing the frequency according to the upwardly convex curve, the frequency is increased according to the downwardly convex curve, and if the load level increases in the middle of increasing the frequency according to the downwardly convex curve, It is possible to control the load level by decreasing the frequency in accordance with a convex curve and changing the frequency between the frequency f1 and an arbitrary driving frequency with hysteresis.

  If the drive frequency is changed in accordance with such a smooth curve, switching in which the number of revolutions rapidly fluctuates is avoided, so that fluctuations in mechanical load can be reduced.

  In the above-described embodiment, an example has been described in which the operating point is determined based on the fluctuation range of the instantaneous load value, and the drive frequency is switched based on the load level that is the average value of the instantaneous load value. A learning unit that sets the drive frequency may be provided in consideration of the processing amount of the object to be crushed by the crushing unit.

  A conveyor-type transport device incorporating a weight scale is provided below the discharge hopper 9 that receives the object to be crushed that has passed through the screen mechanism 8, and the frequency control section 240 inputs the value of the weight scale into the frequency control section 240. 240 can detect the processing amount of the object to be crushed by the crushing unit. At the same time, the frequency control unit 240 can detect the current of the motor M to calculate the average power consumption of the motor M.

  For example, when two sets of operation patterns are set for the upper region operating points (P1, P2) and the lower region operating points (P3, P4) shown in FIG. The average processing amount within a predetermined time detected through the weighing scale when operated at the operating point P1 and the predetermined processing time detected through the weighing scale when operated at the operating point P3 for a predetermined time. A sampling process is performed to compare the average processing amount and select an operating point where the average processing amount increases. At this time, the average power consumption may be calculated at the same time.

  For example, the time during which the pusher mechanism is advanced a predetermined number of times is set as a predetermined time, and the average processing amount can be calculated from the weight detected at intervals of several seconds while the pusher mechanism is advanced a predetermined number of times.

  At the time of learning, it is assumed that the load torque generated by the operation at the operating point P1 is lower than the load level τ3, and the load torque generated by the operation at the operating point P3 is lower than the load level τ1.

  Thereafter, the frequency control unit 240 continues the crushing process at the operating point selected by the learning unit. Since the properties of the workpiece processed by the crushing processing unit change over time, the learning unit continues to monitor the average processing amount, and if the specified amount changes from the initial average processing amount, the drive frequency at that time The average processing amount is stored in the memory, and the sampling process is executed again to select an operating point at which the average processing amount increases.

  By repeating such processing, the learning unit accumulates and stores an appropriate processing amount range and an inappropriate processing amount range for each drive frequency in the memory. Thereafter, when the average processing amount falls within an inappropriate processing amount range, the driving frequency is set so as to increase the processing amount by switching the driving frequency without performing the sampling process.

  When calculating the average power consumption of the motor M at the time of learning, a drive frequency that reduces the average power consumption may be set, or the drive frequency may be set so that the amount of processing for the average power consumption increases. .

  Even when there are a plurality of combinations of operating points as shown in FIG. 11A, an appropriate operating point combination can be selected by learning the average processing amount by the learning unit for the operating points P1 and P2. . The load level to be switched to the second frequency may be set based on the fluctuation range of the instantaneous load value.

  In any case, the frequency control unit 240 controls the drive frequency or the load level with a preset fixed value, or sets the drive frequency or the load level to a different value based on the learning result by the learning unit. It is also possible to provide a switch for selecting either of the control and to input a selection signal from the switch to the frequency control unit 240.

  The learning unit that learns to select one of the preset operating points based on the average processing amount has been described above, but the learning unit learns to adjust the frequency of the preset operating point. Also good.

  Specifically, the value of the first frequency f1 shown in FIG. 9A is changed little by little, the average processing amount at that time is obtained, and the frequency at which the average processing amount is maximum is set as the first frequency. is there. The same applies to the second frequency.

  In the embodiment described above, an example in which a V / f control type inverter circuit is employed as the inverter circuit 230 has been described. However, the inverter circuit 230 employed in the present invention is not limited to a V / f control type inverter circuit. Alternatively, a current vector control type inverter circuit may be employed. In such an inverter circuit, a current having an appropriate current value is supplied to the electric motor with the most efficient phase corresponding to the load fluctuation.

  In the above-described embodiment, the control device of the crushing device including the induction motor that drives the crushing rotor via the speed change mechanism has been described. However, the target of the control device according to the present invention is not limited to the induction motor, and a synchronous motor is used. The present invention can be applied even when controlled by an inverter circuit. When employing a synchronous motor, the crushing rotor may be driven directly without using a speed change mechanism.

  In the above-described embodiment, the control device 200 according to the present invention includes the crushing processing unit that crushes the object to be crushed by the cooperation of the rotary blade fixed to the crushing rotor and the fixed blade arranged to face the rotary blade. Although the case where the present invention is applied to a uniaxial shearing type crushing device has been described, the control device 200 according to the present invention includes a crushing processing unit that crushes an object to be crushed by rotation of a crushing rotor to which a rotary blade is fixed, and a speed change mechanism. Thus, the present invention can be applied to a crushing apparatus including an induction motor that drives a crushing rotor, and can be applied to other types of crushing apparatuses such as a biaxial crushing apparatus.

  Each of the above-described embodiments is an example of the present invention, and the present invention is not limited by the description. The specific configuration of each part can be appropriately changed and designed within the range where the effects of the present invention are exhibited. Needless to say.

1: Crushing device 2: Receiving hopper 3: Pusher pusher 3b: Hydraulic cylinder 4: Base 5: Crushing rotor 6: Crushing rotor 7: Fixed blade 8: Screen mechanism 9: Discharge hopper 10: Crushing processing unit 11: Main body frame 20 : Torque limiter 21: Friction plate 22: Pressurizing plate 23: Supporting part 26: Pressurizing mechanism 26 a: Piston 26 b: Hydraulic chamber 30: Speed change mechanism (deceleration mechanism)
31: Input shaft 37: Output shaft 40: Bearing 47: Second oil passage (supply piping)
50: Pressure reducing valve 51: First oil passage (supply pipe)
52: Hydraulic pump 53: Switching valve 55: Accumulator 56: Pressure sensor 57: Pressure adjusting mechanism 58: Switching valve 100: System control device 200: Motor control device 230: Inverter circuit 240 Frequency control unit M: Driving machine (electric motor)
CL: Center line

Claims (13)

A crushing processing unit for crushing an object to be crushed by rotation of a crushing rotor to which a rotary blade is fixed, and a control device for a crushing device including an electric motor that drives the crushing rotor,
An inverter circuit that drives the motor, and a frequency control unit that switches the output frequency of the inverter circuit from the first frequency to a second frequency different from the first frequency based on the load level of the motor,
The frequency control unit controls the crushing device to have a hysteresis characteristic so that the first load level for switching from the first frequency to the second frequency is different from the second load level for switching from the second frequency to the first frequency. apparatus.   The frequency control unit performs switching with a hysteresis characteristic in which the second load level for switching from the second frequency to the first frequency is set lower than the first load level for switching from the first frequency to the second frequency lower than the first frequency. The control apparatus of the crushing apparatus of Claim 1.   The frequency control unit switches to the second frequency immediately when the load level rises above the first load level, and switches to the first frequency after the state continues for a predetermined time when the load level falls below the second load level. Control device for crushing equipment.   The control of the crushing apparatus according to claim 2, wherein the frequency control unit switches to the second frequency immediately when the load level rises above the first load level, and switches to the first frequency when the load level falls below the second load level after a predetermined time has elapsed. apparatus.   A plurality of sets of the first frequency and the second frequency are set, and a switch for selecting one of the sets is provided, and the frequency control unit corresponds to the first frequency and the second frequency corresponding to the set selected by the switch. The switching is performed with hysteresis characteristics so that the first load level for switching from the first frequency to the second frequency and the second load level for switching from the second frequency to the first frequency are different. The control apparatus of the crushing apparatus in any one.   A plurality of sets of the first load level and the second load level are set, and a switch for selecting any one of the sets is provided, and the frequency control unit includes the first load level and the second load level corresponding to the set selected by the switch. The control apparatus of the crushing apparatus in any one of Claim 2 to 4 which switches from a 1st frequency to a 2nd frequency at a load level, or switches from a 2nd frequency to a 1st frequency.   The control device for a crushing apparatus according to any one of claims 2 to 6, wherein the load level is an average value of instantaneous load values, and the first load level is set to a different value depending on a fluctuation range of the instantaneous load value.   The control device for a crushing apparatus according to any one of claims 2 to 7, wherein the load level is an average value of instantaneous load values, and the first frequency is set to a different value depending on a fluctuation range of the instantaneous load value. The crushing device is provided with a pusher mechanism that is driven back and forth with respect to the crushing processing unit and presses the object to be crushed to the crushing processing unit.
The control device for a crushing apparatus according to claim 7 or 8, wherein the load level is set as an average value of instantaneous load values within a predetermined time at the time of advancing operation to the crushing processing section of the pusher mechanism.   The control device for a crushing apparatus according to any one of claims 2 to 9, wherein an output frequency region of the inverter circuit is divided into a plurality of regions, and a first frequency and a second frequency are set in each region.   A learning unit that sets the first frequency or the second frequency so as to increase the processing amount and / or reduce the power consumption based on the processing amount of the object to be crushed by the crushing processing unit. Item 11. A crusher control device according to any one of Items 1 to 10. A crushing processing unit for crushing an object to be crushed by rotation of a crushing rotor to which a rotary blade is fixed, an electric motor for driving the crushing rotor, and a control method for a crushing device including an inverter circuit for driving the electric motor,
A first load level for switching the output frequency of the inverter circuit from the first frequency to a second frequency different from the first frequency based on the load level of the motor, and a second load level for switching from the second frequency to the first frequency The control method of the crushing device which has a hysteresis characteristic so as to change.   The switching according to claim 12, wherein the second load level for switching from the second frequency to the first frequency is switched to have a hysteresis characteristic set lower than the first load level for switching from the first frequency to the second frequency lower than the first frequency. Control method of crushing device.

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