Powder supply device

Abstract

To more quickly stabilize the discharge flow rate of powder in a powder feeding device.SOLUTION: A powder feeding device comprises a control section for selectively executing: constantly keeping control in which the rotational speed of a motor, or an applied current or an applied voltage to the motor, as a manipulated variable for a prescribed period, is kept constant without any change; and feedback control in which a difference between the discharge flow rate of powder and its target value is repeatedly obtained in prescribed cycles, and the manipulated variable is adjusted to be increased or decreased in each of the cycles in such a direction as to reduce the difference. The control section executes the constantly keeping control immediately after the start of the motor, and shifts to the feedback control if the absolute value of the difference between the discharge flow rate of the powder and its target value falls below a threshold after the elapse of the period of the constantly keeping control, but executes the constantly keeping control without shifting to the feedback control if the absolute value of the difference between the discharge flow rate of the powder and its target value exceeds the threshold after the elapse of the period of the constantly keeping control. The control section changes the manipulated variable when the constantly keeping control is executed again, according to the difference between the discharge flow rate of the powder and its target value after the elapse of the period of the latest constantly keeping control.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a powder supplying device that feeds powder to be discharged. [Background technology]

[0002] 2. Description of the Related Art In a conventional powder supplying device for supplying powder to a rotary compression molding machine or the like, the following control is performed to obtain a desired powder discharge flow rate.

[0003] That is, prior to starting operation, a process called tuning is performed to determine an estimated value of the discharge flow rate when the motor is rotated at maximum speed. After starting operation, it is checked whether the actual discharge flow rate is in line with the target value, and if the actual discharge flow rate differs from the target value, the motor rotation speed is corrected (see, for example, Patent Document 1).

[0004] Conventionally, when the actual discharge flow rate differs significantly from the target value, the discharge flow rate is repeatedly measured at short, predetermined intervals, and the supply amount is corrected by feedback control, which adjusts the motor rotation speed at the same predetermined interval in a direction to reduce the deviation between the actual measured value and the target value. However, this can cause a phenomenon called hunting. While PID control can suppress this phenomenon, it also causes another problem, as shown in Figure 9, in that it takes time for the actual discharge flow rate to approach the target value. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-168634 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention focuses on the above points and has an object to provide a powder supplying device configured to be able to stabilize the powder discharge flow rate more quickly after starting operation. [Means for solving the problem]

[0007] In other words, the powder supplying device of the invention of claim 1 comprises a transfer member for sending out the powder to be discharged, a motor for driving the transfer member, and a control unit for controlling the motor, and the control unit selectively performs constant maintenance control, which keeps the operating variable, which is the motor's rotation speed or the applied current or voltage to the motor, constant for a predetermined period even if the powder discharge flow rate increases or decreases, and feedback control, which repeatedly calculates the difference between the powder discharge flow rate and its target value at a predetermined period and increases or decreases the operating variable at each of the predetermined periods in a direction to reduce the difference.The constant maintenance control is performed immediately after the motor is started, and if the absolute value of the difference between the powder discharge flow rate and its target value falls below a threshold after the constant maintenance control period has elapsed, the control unit switches to the feedback control, while if the absolute value of the difference between the powder discharge flow rate and its target value exceeds the threshold after the constant maintenance control period has elapsed, the control unit does not switch to the feedback control but instead performs constant maintenance control again, and the operating variable in the next constant maintenance control is changed according to the difference between the powder discharge flow rate after the most recent constant maintenance control period has elapsed and its target value.

[0008] The powder supplying device according to the invention of claim 2 comprises a hopper for storing powder, a transfer member for sending out the powder to be discharged, a motor for driving the transfer member, and a control unit for controlling the motor, wherein the control unit selectively performs a constant maintenance control for keeping the rotation speed of the motor or the applied current or voltage to the motor, which is an operation variable, constant for a predetermined period even if the discharge flow rate of the powder increases or decreases, and a feedback control for repeatedly determining the difference between the discharge flow rate of the powder and its target value at predetermined cycles, and adjusting the operation variable by increasing or decreasing it at each of the predetermined cycles in a direction to reduce the difference. The constant holding control is performed immediately after the hopper is filled with powder, and if the absolute value of the difference between the powder discharge flow rate and its target value falls below a threshold value after the period of constant holding control has elapsed, the control switches to the feedback control. On the other hand, if the absolute value of the difference between the powder discharge flow rate and its target value exceeds a threshold value after the period of constant holding control has elapsed, the control does not switch to the feedback control but instead performs constant holding control again, and the manipulated variable in this next constant holding control is changed according to the difference between the powder discharge flow rate and its target value after the most recent period of constant holding control has elapsed.

[0009] In such cases, by setting the range of change between the operating amount in the first constant holding control and the operating amount in the second constant holding control to an appropriate value that is sufficiently larger than the increase or decrease in the operating amount per predetermined period in the feedback control, the number of times constant holding control is performed can be reduced and the amount of powder supply can be made appropriate more quickly.

[0010] One example of a method for determining the powder flow rate in the powder supplying device described above is to measure the powder discharge flow rate based on the mass of the powder in the hopper. In this case, the powder discharge flow rate is measured indirectly based on the mass of the powder actually supplied from the hopper, so the powder discharge flow rate can be measured with high accuracy.

[0011] Furthermore, it is desirable to determine the manipulated variable in the second constant-pressure control by multiplying the manipulated variable in the most recent constant-pressure control by the reciprocal of the ratio of the powder discharge flow rate after the most recent constant-pressure control period to its target value, thereby enabling the powder discharge flow rate to approach the target value more quickly.

[0012] The length of the predetermined period in the constant maintenance control is preferably at least 10 times the predetermined cycle in the feedback control, which allows the amount of powder supply to be stabilized more quickly.

[0013] The term "powder" refers to an aggregate of minute particles, and is a concept that encompasses aggregates of particles such as so-called granules, as well as aggregates of powders smaller than particles. Specific examples of powders include powders containing a main ingredient, as well as excipients, binders, disintegrants, stabilizers, preservatives, etc. Powders containing two or more types of powders are also considered to be a type of powder in the present invention, and powders containing a main ingredient mixed with a lubricant such as magnesium stearate also fall under the category of powder. [Effects of the Invention]

[0014] According to the present invention, it is possible to realize a powder supplying device configured to be able to stabilize the discharge flow rate of powder more quickly after starting operation. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a side cross-sectional view of a rotary powder compression molding machine according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of a main part of the powder compression molding machine according to the embodiment. [Figure 3] FIG. 2 is a cylindrical view of the powder compression molding machine according to the embodiment. [Figure 4] FIG. 2 is a side view schematically showing the configuration of a powder compression molding machine and a powder mixing and supplying system in the embodiment. [Figure 5] FIG. 2 is a side view showing a powder supplying device which is an element of the powder mixing supplying system of the embodiment. [Figure 6]4 is a flowchart showing a flow of control performed by a control unit of the powder supplying device according to the embodiment. [Figure 7] 4 is a time chart illustrating the contents of control by a control unit of the powder supplying device according to the embodiment; [Figure 8] 4 is a time chart illustrating the contents of control by a control unit of the powder supplying device according to the embodiment; [Figure 9] 10 is a time chart illustrating the control performed by a control unit of a conventional powder supplying device. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of the present invention will be described below with reference to the drawings. First, an overview of a rotary powder compression molding machine (hereinafter referred to as a "molding machine") A will be described as an example of equipment that performs post-processing using a mixed powder discharged and supplied by a powder supplying device of this embodiment.

[0017] Molding machine A is a machine that fills mixed powder into a die hole 4 and compresses the powder with punches 5 and 6 to mold pharmaceutical tablets, food products, electronic components, etc. As shown in Figure 1, a vertical shaft 2 that serves as a rotation axis is installed within a frame 1 of molding machine A, and a turntable 3 is attached to the top of the vertical shaft 2 via a connection part 21.

[0018] The turntable 3 rotates horizontally, i.e., spins on its own axis, around the axis of the vertical shaft 2. The turntable 3 is composed of a table (mill disk) 31, an upper punch holder 32, and a lower punch holder 33. As shown in FIG. 2, the table 31 is substantially disk-shaped, and a plurality of mill holes 4 are formed at predetermined intervals along the rotational direction on its outer periphery. The mill holes 4 penetrate the table 31 in the vertical direction. The table 31 may be divided into a plurality of plates. Furthermore, instead of directly drilling the mill holes 4 in the table 31 itself, a configuration may be adopted in which a plurality of mill members that are separate from the table 31 and detachable from the table 31 are attached to the table 31, and a mill hole that penetrates the table 31 in the vertical direction is drilled in each of the mill members.

[0019] An upper punch 5 and a lower punch 6 are arranged above and below each die hole 4. The upper punch 5 and the lower punch 6 are held by an upper punch holder 32 and a lower punch holder 33 so that they can each slide up and down independently relative to the die hole 4. The punch tip 53 of the upper punch 5 moves in and out of the die hole 4. The punch tip 63 of the lower punch 6 is always inserted in the die hole 4. The upper punch 5 and the lower punch 6 rotate horizontally, i.e., revolve, around the axis of the vertical shaft 2 together with the turntable 3 and the die hole 4.

[0020] A worm wheel 7 is attached to the lower end of the vertical shaft 2. A worm gear 10 meshes with the worm wheel 7. The worm gear 10 is fixed to a gear shaft 9 driven by a motor 8. The driving force output by the motor 8 is transmitted to the gear shaft 9 by a belt 11, and drives the vertical shaft 2, the turntable 3, and the punches 5 and 6 to rotate via the worm gear 10 and the worm wheel 7.

[0021] Powder, which is the raw material for a compression-molded product, such as a pharmaceutical tablet, is filled into the die hole 4 through a feeder A1, which is a filling device. There are two types of feeder A1: an agitating feeder and an open feeder, and either type can be used. To supply the powder to the feeder A1, a powder mixing and supplying system B including a powder supplying device, which will be described later, is used. The powder mixing and supplying system B is detachable from the molding machine A.

[0022] 2 and 3, on the revolution orbit of the punches 5, 6 around the axis of the vertical shaft 2, there are a pair of pre-pressing upper roll 12 and pre-pressing lower roll 13, and a pair of main pressure upper roll 14 and main pressure lower roll 15, which sandwich the punches 5, 6. The pre-pressing upper roll 12 and pre-pressing lower roll 13, and the main pressure upper roll 14 and main pressure lower roll 15 urge the upper and lower punches 5, 6 in a direction to move closer to each other so that the powder filled in the die hole 4 is compressed from above and below by the tip surfaces of the punch tips 53, 63.

[0023] The upper punch 5 and the lower punch 6 have heads 51 and 61 pressed by the rolls 12, 13, 14, and 15, respectively, and body portions 52 and 62 having a smaller diameter than the heads 51 and 61. The upper punch holding portion 32 of the turntable 3 holds the body portion 52 of the upper punch 5 so that it can slide up and down, and the lower punch holding portion 33 holds the body portion 62 of the lower punch 6 so that it can slide up and down. The tip portions 53 and 63 of the body portions 52 and 62 are thinner than the other portions so that they can be inserted into the die bore 4, and have a diameter approximately equal to the inner diameter of the die bore 4. As the punches 5 and 6 revolve, the rolls 12, 13, 14, and 15 approach the heads 51 and 61 of the punches 5 and 6 and come into contact with them by climbing up onto the heads 51 and 61. Furthermore, the rolls 12, 13, 14, and 15 press the upper punch 5 downward and the lower punch 6 upward. While the rolls 12, 13, 14, and 15 are in contact with the flat surfaces of the punches 5 and 6, the punches 5 and 6 continue to apply a constant pressure to the powder in the die cavity 4.

[0024] The product discharge section is located further in the direction of rotation of the turntable 3 and punches 5, 6 than the pressure position applied by the main pressure upper roll 14 and main pressure lower roll 15. Here, the lower punch 6 rises until the upper end surface of the punch tip 63 of the lower punch 6 is at approximately the same height as the upper end of the die hole 4, i.e., the upper surface of the table 31, and the molded product inside the die hole 4 is pushed out of the die hole 4. A damper 17 is provided at the product discharge section to guide the molded product pushed out of the die hole 4. The molded product pushed out of the die hole 4 comes into contact with the damper 17 as the turntable 3 rotates, and moves along the damper 17 toward a molded product recovery position 18.

[0025] Next, we will describe the configuration of powder mixed supply system B in this embodiment. This powder mixed supply system B serves to supply mixed powder to equipment that performs post-processing, in this case molding machine A, and as shown in Figure 4, it includes constant-volume feeders B1, B2, and B3, which are multiple powder supply devices that store and discharge the stored powder, and mixers B4 and B5 that mix the powder discharged from each of the multiple constant-volume feeders B1, B2, and B3 and then discharge the mixed powder.

[0026] This powder mixing and supplying system B is equipped with three fixed-volume feeders B1, B2, and B3. However, the number of feeders B1, B2, and B3 varies depending on the number of types of powder to be mixed, and may be two, four, or more. Each feeder B1, B2, and B3 may discharge different types of powder or the same type of powder. The powder discharged by feeders B1, B2, and B3 may be a pre-mixed mixture of multiple powders. Examples of types of powder include powders containing active ingredients, excipients, binders, disintegrants, lubricants, stabilizers, preservatives, etc. In this embodiment, feeder B1, which is a first powder supplying device, ejects and supplies the first powder, which is the main ingredient; feeder B2, which is a second powder supplying device, ejects and supplies the second powder, which is an excipient such as lactose or other powder; and feeder B3, which is a second powder supplying device, ejects and supplies the second powder, which is a lubricant such as magnesium stearate.

[0027] Mixers B4 and B5 consist of a vertical mixer B4 and a horizontal mixer B5 connected downstream. The vertical mixer B4 mixes the powder (i.e., the active ingredient) discharged by feeder B1 with the powder (i.e., excipient or other powder) discharged by feeder B2, dropping the mixture toward the horizontal mixer B5. The vertical mixer B4 has a funnel-shaped case B41, a vertical or nearly vertical agitator shaft B42 that rotates on its own axis and is located in the center of the case, an agitator blade B43 attached integrally to the agitator shaft, and a motor B44 that rotates the agitator shaft B42 and agitator blade B43.

[0028] The powders discharged from feeder B1 and feeder B2 are dropped from above into the case of vertical mixer B4. The powders come into contact with rotating agitator blade B43 and move downward within case B41 while being agitated by the agitator blade B43. A number of holes (not shown) that penetrate case B41 are pre-drilled in the bottom of case B41, and the mixed powder agitated within case B41 flows out of case B41 through these holes. The mixed powder then flows into horizontal mixer B5 through connection port B45.

[0029] The horizontal mixer B5 mixes the powders mixed in the vertical mixer B4, i.e., the main drug and excipients or other powders, with the powders discharged by the feeder B3, i.e., the lubricant, and transfers them toward the feeder A1 of the molding machine A. The horizontal mixer B5 has a cylindrical case B51 extending horizontally or approximately horizontally, a horizontal or approximately horizontal agitator shaft B52 located in the center of the case B51 and rotating on its own axis, an agitator blade B53 attached to the agitator shaft B52, and a motor B54 that rotates the agitator shaft B52 and agitator blade B53.

[0030] The outer end of the case B51 is provided with an inlet B511 that connects to the connection port of the vertical mixer B4. The inner end of the case B51 is provided with a discharge port B512 that connects the inside and outside of the feeder A1 and connects to the supply port A11 for supplying powder to the feeder A1. Furthermore, the middle of the case B51 is provided with an inlet B513 that connects to the feeder B3. The agitator shaft B52 and agitator blade B53 rotate while in contact with the powder to be mixed, mixing the powder and transporting the powder in a direction intersecting the vertical direction. These agitators B52 and B53 extend to just before the discharge port B512, which is the end of the mixers B4 and B5.

[0031] The powder mixed in the vertical mixer B4 is fed from the connection port B45 through the receiving port B511 into the case B51 of the horizontal mixer B5. The powder comes into contact with the rotating agitator blade B53 and moves from the outside to the inside of the case B51 while being agitated by the agitator blade B53. During this process, powder discharged from the feeder B3 is fed into the case B51 through the receiving port B513 and further agitated by the agitator blade B53. As a result, the main ingredient supplied by the feeder B1, the excipient or other powder supplied by the feeder B2, and the lubricant supplied by the feeder B3 are mixed within the case B51 and transported along the case B51. Finally, this mixed powder is discharged from the discharge port B512 and supplied to the feed port A11 of the feeder A1 of the molding machine A. The feeder A1 fills the mixed powder supplied to its feeding port A11 into the die hole 4 drilled in the table 31.

[0032] A sensor (not shown) is installed in advance in the feeder A1 to measure the mixing degree of the mixed powder supplied from the powder mixing supply system B. Various methods for measuring the mixing degree of powders include Raman spectroscopy, infrared spectroscopy, X-ray diffraction, X-ray transmission measurement, and high-performance liquid chromatography (HPLC). Any method capable of measuring the mixing degree in real time is acceptable. For example, near-infrared spectroscopy (NIR, or near-infrared absorption spectroscopy) is used to evaluate the amount or proportion (ratio) of the active ingredient in the mixed powder, in other words, the homogeneity of the mixed powder (whether segregation occurs). Near-infrared spectroscopy irradiates the moving mixed powder with near-infrared light, measures the absorption and scattering of light, and performs qualitative and quantitative analysis of the active ingredient concentration and other parameters at predetermined intervals. The wavelength used for measurement is a wavelength band that has no peaks for excipients or lubricants and is characterized by the absorption peak of the active ingredient. Near-infrared spectroscopy can also be used to measure the particle size of the mixed powder. When near-infrared spectroscopic analysis is employed, a near-infrared sensor is installed in the feeder A1 as a PAT (Process Analytical Technology) sensor that measures the degree of mixing of powders, etc.

[0033] In addition, the product discharge section of molding machine A is provided with a molded product rejection mechanism W for sorting out specific molded products, such as defective products or sample products, from a group of molded products to be collected at molded product collection position 18. Specifically, an air passage 16 for circulating pressurized air is formed inside damper 17, and the tip of this air passage 16 is an air injection nozzle 16a that opens outward in the radial direction of turntable 3. A control valve 22 for opening and closing passage 20 is installed on a flow path 20 that connects an air supply source (not shown), such as a pump that supplies pressurized air, to air passage 16. Control valve 22 is, for example, an electromagnetic solenoid that opens and closes in response to a control signal given from a control device.

[0034] When the control valve 22 is opened as a specific molded product extruded from the die bore 4 passes near the air injection nozzle 16a before coming into contact with the damper 17, pressurized air supplied from the air supply source is ejected from the air injection nozzle 16a via the flow path 20 and the air passage 16 in the damper 17. This ejected air blows the specific molded product outward from the table 31. The blown-away molded product does not reach the molded product recovery position 18 located further along the damper 17. Thus, in this molding machine A, the flow passages 16, 20 for the air supplied from the air supply source, the injection nozzle 16a, and the control valve 22 constitute a molded product removal mechanism W.

[0035] If the composition or degree of mixing of the powder mixture measured by a near-infrared sensor or the like attached to the feeder A1 is found to be inappropriate, the powder mixture is first loaded from the feeder A1 into the die hole 4 of the table 31 of the molding machine A, and then compressed into a molded product by the upper punch 5 and the lower punch 6. The molded product is then removed by the molded product removal mechanism W before reaching the molded product recovery position 18. That is, in the molding machine A, when the die hole 4 filled with the defective powder mixture and into which the molded product has been tableted passes near the air injection nozzle 16a, the control valve 22 is opened and air is injected from the air injection nozzle 16a to blow the molded product out of the table 31. At the same time, an alarm may be sounded, the device may be stopped, etc.

[0036] When connecting the powder mixing supply system B to the molding machine A, the inner end of the case B51 of the horizontal mixer B5 and the discharge port B512 are inserted into the frame 1 of the molding machine A. Meanwhile, the other elements of the powder mixing supply system B, i.e., the parts of the horizontal mixer B5 other than the inner end of the case B51, the vertical mixer B4, and the constant feeders B1, B2, and B3, remain outside the frame 1 of the molding machine A. Casters B7 are attached to the bottom of the support body (frame or housing) B6 of the powder mixing supply system B that supports the constant feeders B1, B2, and B3, the vertical mixer B4, and the horizontal mixer B5, to enable the powder mixing supply system B to be easily moved.

[0037] The following provides additional information regarding the structure of constant-volume feeders B1, B2, and B3. As shown in Figure 5, each of feeders B1, B2, and B3 includes a hopper B01 for storing powder, a transfer mechanism B02 for delivering the powder from the hopper B01 so that it can be discharged, a supply mechanism B03 for supplying powder to the hopper B01 at appropriate times, a measuring device B04 for measuring the discharge flow rate per unit time of the powder discharged by the transfer mechanism B02, and a control unit B05 for controlling the transfer mechanism B02 so that the discharge flow rate of the powder converges to a required target value.

[0038] The transfer mechanism B02 includes a transfer member B021 that contacts and transfers powder falling from the hopper B01, and a motor B022 that rotates and drives the transfer member B021. The transfer mechanism B02 can be, for example, a known screw feeder, table feeder, circle feeder (registered trademark), disk feeder, or rotary feeder. The transfer member B021 in the screw feeder B02 is a screw blade with spiral blades attached to a shaft that rotates around its axis, and transfers powder captured between the blades along the axis. The transfer members in the table feeder, circle feeder (registered trademark), disk feeder, and rotary feeder are a rotating table, flat bar (rotating blade), disk, and rotor (built into a rotary valve), respectively. In this embodiment, a screw feeder is used as the transfer mechanism B02. The rotation speed of the motor B022 that drives the transfer member B021 affects the flow rate per unit time of the powder delivered by the transfer mechanism B02. In principle, the higher the rotation speed of the motor B022, the greater the flow rate of the powder delivered per unit time.

[0039] The motor B022 (and the motor B032 of the supply mechanism B03 described below) is, for example, a DC (direct current) motor, particularly a brushless DC motor. The basic characteristics of a DC motor are: V M =I a R a +E a E a =K e N T=K t I a =-(K t K e N) / R a +(K t V M ) / R a where V M is the power supply voltage applied to the coil of the DC motor, I a is the current flowing through the coil of the DC motor, R a is the armature resistance, E a is the back electromotive force voltage, T is the torque generated by the DC motor, K t is the torque constant, K e is the back electromotive force constant, and N is the rotation speed of the DC motor.

[0040] The supply mechanism B03 is, for example, a known rotary feeder, and is located above the hopper B01. It stores a large amount of powder to be supplied to the hopper B01. A rotary valve B031 is installed below the supply mechanism B03, facing the hopper B01. When the amount of powder in the hopper B01 decreases to a predetermined lower limit, the supply mechanism B03 opens the rotary valve B031 to feed the stored powder into the hopper B01. When the amount of powder in the hopper B01 recovers to a predetermined upper limit, the rotary valve B031 is closed to prevent any further powder from being fed into the hopper B01.

[0041] The measuring instrument B04 repeatedly detects the current weight of the hopper B01 and the powder stored in the hopper B01. The value subtracted from this weight is the powder discharge amount of the constant-weight feeders B1, B2, and B3. The measuring instrument B04 may be, for example, a load cell, which is a strain gauge sensor, a tuning fork force sensor, or a force balance sensor. The supply mechanism B03 and the hopper B01 are connected via, for example, a bellows joint B033, so that the weight of the supply mechanism B03 and the weight of the powder stored in the supply mechanism B03 (before being supplied to the hopper B01) are not added to the hopper B01. In other words, the measuring instrument B04 does not detect the weight of the supply mechanism B03 or the powder stored in the supply mechanism B03.

[0042] The control unit B05 receives an output signal from the measuring device B04 to determine the weight of powder currently stored in the hopper B01, and controls a motor B022 that drives a transfer member (i.e., a screw blade of the screw feeder) B021 in the transfer mechanism B02, and a motor B032 that drives a rotor of a rotary valve B031 in the supply mechanism B03. The control unit B05 includes, as elements, a known motor driver that switches the operation of the motors B022 and B032 on and off and controls the rotation speed or output torque of the motors B022 and B032, and a microcomputer, programmable controller, general-purpose personal computer, workstation, or the like that commands the motor driver to realize the rotation speed or output torque of the motors B022 and B032. The motor driver rotates the motors B022 and B032 by sequentially applying current to the coils of each phase contained in the motors B022 and B032, and controls the rotation speed and output torque of the motors B022 and B032. Increasing the current and / or voltage applied to the coils of the motors B022 and B032 increases the output torque of the motors B022 and B032 and increases the rotation speed. Decreasing the current and / or voltage applied to the coils of the motors B022 and B032 reduces the output torque of the motors B022 and B032 and decreases the rotation speed. When controlling the motors B022 and B032, the magnitude of the current flowing through the coils may be increased or decreased using PWM (Pulse Width Modulation) control.

[0043] The control unit B05 of the constant-volume feeders B1, B2, and B3 of this embodiment basically uses a loss-in-weight method (integrated weight loss method) to perform feedback control (e.g., PID control) on the discharge flow rate per unit time of the powder discharged by the feeders B1, B2, and B3. Specifically, the weight of the powder lost from the hopper B01 by being sent out by the transfer mechanism B02 is constantly measured by a measuring device B04, and the progress of the weight decrease is compared to a preset target value for the discharge flow rate. The control unit B05 increases or decreases the rotation speed and / or output torque of the motor B022, which are manipulated variables, in a direction that reduces the deviation between the two, thereby increasing or decreasing the discharge flow rate of the powder from the feeders B1, B2, and B3.

[0044] In addition, as already described, when the amount of powder in the hopper B01 falls to a predetermined lower limit, the control unit B05 activates the motor B032 that drives the rotor of the rotary valve B031 of the supply mechanism B03 to feed the powder stored in the supply mechanism B03 into the hopper B01. Then, when the amount of powder in the hopper B01 recovers to a predetermined upper limit, the control unit B05 stops the operation of the motor B032 to prevent any more powder from being fed into the hopper B01.

[0045] In this embodiment, the control unit B05 selectively performs constant maintenance control, which keeps the applied current to the motor B022, which is the manipulated variable, constant for a predetermined period even if the powder discharge flow rate increases or decreases, and feedback control, which repeatedly calculates the difference between the powder discharge flow rate and its target value at predetermined intervals and increases or decreases the applied current to the motor B022 at each of the predetermined intervals in a direction to reduce the difference.The following control is performed immediately after startup and in the time period immediately after the powder stored in the replenishing mechanism B03 is put into the hopper B01. Specifically, the control unit B05 performs the constant flow control immediately after starting the motor B022 and immediately after adding powder to the hopper B01. If the absolute value of the difference between the powder discharge flow rate and its target value is less than or equal to a threshold value after the constant flow control period has elapsed, the control unit B05 transitions to the feedback control described above. If the absolute value of the difference between the powder discharge flow rate and its target value is greater than or equal to the threshold value after the constant flow control period has elapsed, the control unit B05 does not transition to the feedback control and instead performs the constant flow control again. In this repeated constant flow control, the current applied to the motor B022 is controlled based on the difference between the powder discharge flow rate after the most recent constant flow control period and its target value. In this control, the magnitude of the current flowing through the coil is controlled using pulse width modulation (PWM). Prior to startup, tuning is performed to determine the duty ratio corresponding to the target value of the powder discharge flow rate. During the first constant flow control, a current is applied to the coil of the motor B022 at the duty ratio determined during tuning.

[0046] 6, a constant maintenance control is performed (step S1), and the powder discharge flow rate is measured (step S2). More specifically, a signal indicating the mass of powder lost from the hopper B01 is received from a measuring instrument B04, and the rate at which that mass is reduced is taken as the powder discharge flow rate.

[0047] Then, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate and the target value F0 is set as the threshold value F sIf it exceeds this (step S3), the reciprocal F0 / F1 of the ratio of the actual measured value F1 of the discharge flow rate to the target value F0 is multiplied by the current I1 applied to the motor B022 in the most recent constant maintenance control to determine a new current I2 applied to the motor B022 (step S4), and constant maintenance control is performed again (step S1).

[0048] On the other hand, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate and the target value F0 is the threshold value F s If it is below this, the process shifts to feedback control (step S5).

[0049] 7 and 8 show the transition of the powder discharge flow rate and the motor rotation speed immediately after startup.

[0050] FIG. 7 shows that the actual measured value F1 of the powder discharge flow rate corresponding to the current applied to the motor B022 during the first constant maintenance control does not differ significantly from the target value F0. In other words, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate immediately after the first constant maintenance control and the target value F0 is smaller than the threshold value F1. s As described above, immediately after the start of the motor B022, even if the powder discharge flow rate increases or decreases, constant maintenance control is performed to keep the applied current I1 to the motor B022, which is the manipulated variable, constant for a predetermined period. Then, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate at time T1 immediately after the constant maintenance control is performed once and the target value F0 is equal to or less than the threshold value F s Since the output voltage is below , the control immediately shifts to feedback control.

[0051] In FIG. 8, the actual measured value F1 of the powder discharge flow rate corresponding to the current applied to the motor B022 in the first constant maintenance control is significantly different from the target value F0. In other words, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate immediately after the first constant maintenance control is performed and the target value F0 is greater than the threshold value F1. sIn this case, immediately after the start of the motor B022, even if the powder discharge flow rate increases or decreases, constant maintenance control is performed to keep the applied current I1 to the motor B022, which is the manipulated variable, constant for a predetermined period without changing it. However, the absolute value |ΔF1| of the difference between the actual measured value F1 of the discharge flow rate at time T1 immediately after the constant maintenance control is performed once and the target value F0 is greater than the threshold value F s Since the current I1 applied to the motor B022 in the most recent constant maintenance control is multiplied by the reciprocal F0 / F1 of the ratio of the actual discharge flow rate F1 to the target value F0 to determine a new current I2 applied to the motor B022, and constant maintenance control is performed again.Then, since the absolute value |ΔF2| of the difference between the actual discharge flow rate F2 and the target value F0 at time T2 immediately after the second constant maintenance control is performed is below the threshold value F2, the system switches to feedback control.

[0052] Here, the control unit B05 changes the duty ratio of the current applied to the motor B022 in accordance with the target value F0 of the discharge flow rate and the actual measured values ​​F1 and F2, and Figures 7 and 8 show the actual measured values ​​of the apparent current magnitude.

[0053] The length of the predetermined period in the constant maintenance control is 10 times or more the predetermined cycle in the feedback control, and is specifically set to several seconds or more, preferably 10 seconds or more, and more preferably 20 seconds or more.

[0054] With this configuration, the powder discharge flow rate is measured immediately after startup and immediately after powder is replenished into the hopper B01, and if the absolute value of the difference between the actual measured value F1 of the discharge flow rate and the target value F0 exceeds the threshold value, constant maintenance control is performed again without switching to feedback control, and the current I1 applied to the motor B022 in this constant maintenance control is changed according to the difference between the actual measured value F1 of the powder discharge flow rate after the most recent constant maintenance control period has elapsed and its target value F0.Therefore, the amount of change in the current applied to the motor B022 can be made larger than when the amount of change in the current applied to the motor B022 is made in feedback control as shown in Figure 9, and as a result, the amount of powder supplied can be stabilized more quickly.

[0055] In addition, the current I2 applied to motor B022 in the next constant maintenance control is determined by multiplying the current I1 applied to motor B022 in the most recent constant maintenance control by the reciprocal F0 / F1 of the ratio between the powder discharge flow rate F1 after the most recent constant maintenance control period has elapsed and its target value F0, so the powder discharge flow rate can be brought closer to the target value more quickly.

[0056] The present invention is not limited to the above-described embodiment.

[0057] For example, in the above-described embodiment, the magnitude of the current applied to the motor is used as the manipulated variable and is changed by PWM control, but the magnitude of the current may be changed by other methods.Furthermore, the voltage applied to the motor or the motor rotation speed may also be used as the manipulated variable.

[0058] Furthermore, in the above-described embodiment, the control according to the present invention is performed immediately after starting the motor and immediately after refilling the hopper with powder, but even if the above-described control is performed only immediately after starting the motor, the powder discharge flow rate can be stabilized more quickly at least immediately after starting the motor.

[0059] Furthermore, in the above-described embodiment, the flow rate is proportional to the rotational speed of the motor, and the rotational speed of the motor is normally proportional to the current applied to the motor. Therefore, the duty ratio of the current, which is the manipulated variable in the second constant-flow control, is determined by multiplying the duty ratio of the current in the most recent constant-flow control by the reciprocal of the ratio of the powder flow rate to the target value at a predetermined time after startup. However, if the rotational speed of the motor is not necessarily proportional to the current applied to the motor, it is preferable to determine the manipulated variable in the second constant-flow control by another method. For example, a map showing the relationship between typical discharge flow rates and corresponding current magnitudes may be built in, and the current magnitude corresponding to the desired discharge flow rate may be determined by interpolation.

[0060] Furthermore, the predetermined period in the constant maintenance control may be set arbitrarily.

[0061] In addition, various modifications may be made without departing from the spirit of the present invention. [Explanation of symbols]

[0062] B1, B2, B3... Powder supply device (quantitative supply feeder) B01…Hopper B021...Transfer member B022...Motor B05...Control unit F1, F2...Measured powder discharge flow rate F0: Target value of powder discharge flow rate

Claims

1. The device includes a transfer member for sending out powder to be discharged, a motor for driving the transfer member, and a control unit for controlling the motor, The control unit a constant maintenance control that keeps the rotation speed of the motor or the applied current or voltage to the motor, which is an operation amount, constant for a predetermined period even if the discharge flow rate of the powder increases or decreases; a feedback control that repeatedly calculates the difference between the powder discharge flow rate and its target value at a predetermined cycle, and adjusts the manipulated variable by increasing or decreasing it at the same predetermined cycle in a direction to reduce the difference; Immediately after starting the motor, the constant-current maintaining control is performed; After the period of the constant maintenance control has elapsed, if the absolute value of the difference between the powder discharge flow rate and its target value falls below a threshold, the control is switched to the feedback control, If, after the period of constant maintenance control has elapsed, the absolute value of the difference between the powder discharge flow rate and its target value exceeds a threshold value, the powder supply device will perform constant maintenance control again without transitioning to the feedback control, and will change the operating amount in this constant maintenance control again depending on the difference between the powder discharge flow rate after the most recent period of constant maintenance control has elapsed and its target value.

2. The powder dispenser includes a hopper for storing powder, a transfer member for sending out the powder to be discharged, a motor for driving the transfer member, and a control unit for controlling the motor, The control unit a constant maintenance control that keeps the rotation speed of the motor or the applied current or voltage to the motor, which is an operation amount, constant for a predetermined period even if the discharge flow rate of the powder increases or decreases; a feedback control that repeatedly calculates the difference between the powder discharge flow rate and its target value at a predetermined cycle, and adjusts the manipulated variable by increasing or decreasing it at the same predetermined cycle in a direction to reduce the difference; Immediately after the powder is filled into the hopper, the constant maintenance control is performed; After the period of the constant maintenance control has elapsed, if the absolute value of the difference between the powder discharge flow rate and its target value falls below a threshold, the control is switched to the feedback control, If, after the period of constant maintenance control has elapsed, the absolute value of the difference between the powder discharge flow rate and its target value exceeds a threshold value, the powder supply device will perform constant maintenance control again without transitioning to the feedback control, and will change the operating amount in this constant maintenance control again depending on the difference between the powder discharge flow rate after the most recent period of constant maintenance control has elapsed and its target value.

3. A hopper for storing powder is provided.

3. The powder supplying device according to claim 1, wherein the discharge flow rate of the powder is measured based on the mass of the powder in the hopper.

4. 4. The powder supplying device according to claim 1, wherein the manipulated variable in the second constant maintenance control is determined by multiplying the manipulated variable in the most recent constant maintenance control by the reciprocal of the ratio of the powder discharge flow rate after the period of the most recent constant maintenance control has elapsed to its target value.

5. 5. A powder supplying device according to claim 1, wherein the length of the predetermined period in the constant maintenance control is at least 10 times the predetermined cycle in the feedback control.

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