Source: https://patents.google.com/patent/JP2011016210A/en
Timestamp: 2019-12-07 10:36:45
Document Index: 402199251

Matched Legal Cases: ['art 31', 'art 32', 'art 32', 'art 32', 'art 6', 'art 7', 'art 8', 'art 26', 'art 27', 'art\n28', 'art) 30']

JP2011016210A - Power tool - Google Patents
JP2011016210A
JP2011016210A JP2009163941A JP2009163941A JP2011016210A JP 2011016210 A JP2011016210 A JP 2011016210A JP 2009163941 A JP2009163941 A JP 2009163941A JP 2009163941 A JP2009163941 A JP 2009163941A JP 2011016210 A JP2011016210 A JP 2011016210A
target rotational
JP2009163941A
JP5408535B2 (en
和隆 岩田
嶋　敏洋
2009-07-10 Application filed by Hitachi Koki Co Ltd, 日立工機株式会社 filed Critical Hitachi Koki Co Ltd
2009-07-10 Priority to JP2009163941A priority Critical patent/JP5408535B2/en
2011-01-27 Publication of JP2011016210A publication Critical patent/JP2011016210A/en
2014-02-05 Publication of JP5408535B2 publication Critical patent/JP5408535B2/en
An electric tool capable of stably rotating a motor according to a set target rotational speed of the motor is provided.
The motor stops in a power tool having a motor, a drive circuit that supplies power from the power source to the motor, and a control unit that rotates the motor at the target rotational speed set in the set mode. A voltage detection circuit for detecting the voltage value of the power supply during operation is provided, and the target rotational speed is variably set based on the detected voltage value. The electric tool includes a switch trigger for rotating the motor, and the control unit measures the voltage value after the switch trigger is turned on and before the motor rotates, and the target is based on the measured voltage value. The rotation speed was set.
The present invention relates to motor control of an electric tool, and more particularly to an electric tool with improved motor control when a power supply voltage is lowered.
In screw tightening electric tools such as driver drills, before starting the screw tightening operation, select a predetermined number of rotations from among a number of motor rotations that can be set, and rotate the motor at the selected number of rotations. Do work. Such a motor control method is known, for example, from Patent Document 1. A method of selecting the number of rotations is known using a mode selection dial or a method of selecting a tact switch by pressing a tact switch a predetermined number of times. By making it possible to select a plurality of motor rotation speeds, a wide range of work from low load work to high load work can be performed efficiently. What is important when performing screw tightening work is to improve the follow-up performance of the motor to the trigger operation of the operator and to stabilize the motor without stopping until the trigger operation is canceled by releasing the trigger operation. To complete the work.
FIG. 14 shows the motor characteristics indicating the relationship between the rotational speed of the motor and the generated torque in the conventional electric tool, and the target rotational speed in each speed mode. This motor characteristic is a characteristic when the power supply voltage is in a fully charged state, and the number of rotations of the motor at no load is N 0 (rpm). As the load applied to the motor increases, the rotational speed of the motor decreases in inverse proportion, and the rotational speed becomes zero at the time of the torque T0. In an electric tool using a motor having such characteristics, for example, three target rotational speeds are set as the rotational speed mode. When the target rotational speed is set, the control unit of the electric tool performs control using any known control method (for example, PID control) so as to rotate the motor at the target rotational speed.
FIG. 15 illustrates the motor rotation control status using PID control. In FIG. 15, the vertical axis represents the motor rotation speed (rpm) or the PWM duty (%) of the switching element that drives the motor. At time 0, the motor is started, and the duty ratio of the pulse width of the PWM drive signal (hereinafter referred to as “PWM duty”) is increased to 100% as indicated by an arrow c1. This is because if the PID control is performed in this section, the difference between the target rotational speed and the actual rotational speed is large, so feedback control is performed to increase the PWM duty. With this control, the rotational speed of the motor increases as shown by arrow b1. In the area indicated by the arrow c2, the difference between the target rotational speed and the actual rotational speed has become smaller, so feedback control is performed to reduce the PWM duty. As a result, the motor is driven at the target rotational speed Nt as indicated by the arrow b2. Constant speed control. When the motor rotates at a constant speed at the target rotation speed Nt, the duty is maintained at a predetermined value as indicated by an arrow c3.
If the load applied to the motor increases for some reason at the time indicated by the arrow b3 in FIG. 15, the rotational speed of the motor temporarily decreases from the target rotational speed as indicated by the arrow b4. At this time, since a difference between the target rotational speed of the motor and the actual rotational speed has occurred, the PWM duty is controlled to be increased at the time point c4 by PID control. Thereafter, the increased duty is operated at a PWM duty for rotating the motor at the target rotational speed as indicated by an arrow c5, and the motor is driven at a constant speed at the target rotational speed as indicated by arrows b5 and b6. Rotate.
JP-A-9-65675
FIG. 5 shows the relationship between the target rotational speed and the motor characteristic m3 in each mode when the remaining battery level of the battery pack 30 is reduced. As can be understood from this figure, when the remaining battery level is low, the motor characteristic m3 does not intersect with any of the target rotational speeds of modes 1 to 3, so that the motor is rotated at any target rotational speed of modes 1 to 3. I can't do that. For this reason, there is an adverse effect that the rotational speed cannot be controlled and the workability is deteriorated even though the operator intentionally switches the speed mode.
The present invention has been made in view of the above background, and an object thereof is to provide an electric tool capable of stably rotating a motor in accordance with a set target rotational speed of the motor.
Another object of the present invention is to provide an electric tool capable of avoiding unstable operation of a motor due to a voltage drop of a battery pack.
Still another object of the present invention is to provide an electric tool that performs constant speed control with high accuracy so as to achieve a target rotational speed during rotation of a motor.
The characteristics of representative ones of the inventions disclosed in the present application will be described as follows.
According to one aspect of the present invention, a motor, a drive circuit that supplies electric power from a power source to the motor, and a target rotational speed in a plurality of modes are provided, and the motor is rotated at the set target rotational speed. In the electric tool having a portion, a voltage detection circuit for detecting the voltage value of the power supply when the motor is stopped is provided, and the target rotational speed is variably set based on the detected voltage value. The electric tool includes a switch trigger for rotating the motor, and the control unit measures the voltage value after the switch trigger is turned on and before the motor rotates, and the target is based on the measured voltage value. The rotation speed was set.
According to another feature of the present invention, the electric tool has a changeover switch for setting the target rotational speed, and the control unit measures and measures a voltage value when the target rotational speed is changed by the changeover switch. Set the target speed based on the measured voltage value. This target rotational speed is preferably set so as to increase or decrease in proportion to the power supply voltage.
According to still another aspect of the present invention, the drive circuit is an inverter circuit including a semiconductor switching element, and the control unit controls the rotation of the brushless DC motor by controlling the PWM duty supplied to the inverter circuit. The control unit performs constant speed control so that the rotational speed of the motor becomes the target rotational speed by performing PID control on the PWM duty. The gain of PID control is changed based on the measured voltage value, but the control gain is preferably increased in inverse proportion to the voltage value.
According to the first aspect of the present invention, the voltage detection circuit for detecting the voltage value of the power supply when the motor is stopped is provided, and the target rotational speed is variably set based on the detected voltage value. Even if the voltage changes, the target rotation speed can be appropriately switched.
According to the invention of claim 2, since the voltage value of the power supply is measured before the motor rotates, and the target rotation speed is set based on the measured voltage value, the optimum value corresponding to the power supply voltage before each operation is set. A target rotation speed can be set.
According to the invention of claim 3, the control unit measures the power supply voltage when the target rotational speed is changed by the changeover switch, and sets the target rotational speed based on the measured voltage value. Since the target rotational speed is not changed unless is operated, the target rotational speed does not vary and uniform work can be performed.
According to the fourth aspect of the invention, the target rotational speed is set so as to increase or decrease in proportion to the power supply voltage, so that the target rotational speed can be appropriately switched even if the power supply voltage changes.
According to the fifth aspect of the present invention, since the control unit controls the rotation of the motor by controlling the PWM duty supplied to the inverter circuit, the rotation control of the motor can be performed with high efficiency and high accuracy.
According to the sixth aspect of the present invention, the control unit controls the PWM duty by PID control, thereby performing constant speed control so that the rotational speed of the motor becomes the target rotational speed. It can be carried out. Further, even when the rotation of the motor is disturbed due to a change in load or the like, the target rotation speed can be immediately restored.
According to the seventh aspect of the present invention, since the control unit changes the gain of PID control based on the measured voltage value, the controllability of PID control can be improved.
According to the eighth aspect of the present invention, the control gain to be changed is increased in inverse proportion to the power supply value. Therefore, when the power supply voltage is relatively low, the feedback gain is increased and the followability to the target rotational speed is maintained. When the power supply voltage is relatively high, the feedback gain is reduced to prevent the occurrence of overshoot. As a result, constant rotation speed control can be accurately performed regardless of the power supply voltage.
According to the ninth aspect of the invention, since the motor used is a brushless DC motor, it is possible to perform highly accurate rotation control, and to realize an electric tool with high efficiency and low power consumption.
It is a figure which shows the whole electric tool which concerns on the Example of this invention, and shows the cross section in part. It is a figure which shows typically the cross-section of the motor 2 of FIG. It is a functional block diagram of the electric tool which concerns on the Example of this invention. It is a figure which shows the relationship between the rotation speed of a motor, and output torque. It is a graph which shows the relationship between the rotation speed of a motor and output torque when a power supply voltage falls. It is a graph which shows the power supply voltage of a motor, and the target rotation speed at each mode. It is a graph which shows the relationship between the rotation speed of a motor and output torque when a power supply voltage falls. It is a flowchart which shows the control procedure of the motor in the Example of this invention. It is a figure for demonstrating the condition which changes the target rotation speed at the time of switching the speed mode of a motor in the Example of invention. It is a flowchart which shows the control procedure of the motor in 2nd Example of this invention. It is a graph which shows the fixed control of PWM duty, and the relationship between the rotation speed of the motor at the time of PID control, and a motor current. It is a graph which shows the relationship between the various gains and power supply voltage which are used by PID control. It is a flowchart which shows the control procedure of the motor in the 3rd Example of this invention. It is a graph which shows the relationship between the rotation speed in the case of the conventional PWM duty fixed control of a motor, and the constant speed control system, and an electric current. It is a graph which shows the rotation speed in the conventional constant speed control system of a motor, the relationship between PWM duty, and time.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description of the present specification, the up and down and front and rear directions will be described as the directions shown in FIG. FIG. 1 is a diagram showing an entire electric power tool according to an embodiment of the present invention, and a part thereof is shown in cross section. In this embodiment, a driver drill 1 will be described as an embodiment of the power tool. However, the present invention is not limited to this, and other power tools such as an impact driver and a hammer drill may be used.
In FIG. 1, a driver drill 1 houses a motor 2 in a body housing portion 6a, and is detachably attached to a chuck 28 attached to a spindle (output shaft) 8 by a power transmission portion 25 that transmits a driving force of the motor 2. A rotational force is applied to a screwdriver or drill tip tool (not shown) held by the tool. An inverter circuit portion (circuit board) 3 for driving the motor 2 is accommodated on the rear side of the body housing portion 6a, and in the direction of the rotating shaft 2e of the motor 2 on the middle portion and the front side of the body housing portion 6a. A speed reduction mechanism portion 26 for transmitting the rotational force and reducing the rotational speed of the motor 2 and a clutch mechanism portion 27 for transmitting the rotational torque obtained at the output shaft of the speed reduction mechanism portion 26 to the spindle 8 are housed. The clutch mechanism 27 is coupled so as to transmit the rotational force of the speed reduction mechanism 26 to the spindle (output shaft) 8. Further, a normal impact mechanism may be provided instead of the clutch mechanism portion 27.
The clutch mechanism 27 has a dial (clutch dial) 5 for mode switching and torque adjustment, and the dial 5 is configured so that an operator can set a driver mode or a drill mode. When the dial 5 is in the driver mode, the clutch mechanism 27 is rotated from the output shaft of the speed reduction mechanism 26 according to the rotation angle of the dial 5 by rotating the torque adjustment dial 5 to a predetermined rotation angle in a plurality of stages. The rotational torque transmitted to the spindle 8 can be adjusted to a desired tightening torque corresponding to the load. The dial 5 can be set, for example, in 10 stages of torque. When a load torque higher than the set tightening torque (sliding torque) is applied to the spindle 8, the output shaft of the speed reduction mechanism unit 26 is disconnected from the coupling with the spindle 8 by the clutch mechanism of the torque adjustment unit 5, and idles. This prevents the motor 2 from being locked.
When the dial 5 is set to the drill mode, the dial 5 is rotated to the maximum rotation angle so that the rotational force obtained by the speed reduction mechanism unit 26 is switched to be transmitted to the spindle 8 without operating the clutch. When the load is larger than the tightening torque of the spindle in this drill mode, the clutch function does not work, so the tip tool held on the spindle is locked and the motor 2 is locked. The reduction mechanism unit 26 is configured by a well-known technique and meshes with a pinion gear formed at the front end of the rotating shaft 2e of the motor 2, for example, a two-stage planetary gear reduction mechanism (transmission gear case) (not shown). Consists of
In this embodiment, the motor 2 uses a three-phase brushless DC motor. FIG. 2 is a diagram schematically showing a cross-sectional structure of the motor 2 of FIG. This cross section is a plane cut perpendicular to the output rotation axis of the motor 2. As shown in FIG. 2, the motor 2 includes a rotor (rotor) 2a and a stator winding (armature winding) 2d. The rotor 2a has N-pole and S-pole permanent magnets (magnets) 2b extending in the direction of the rotation shaft 2e, and the stator 2c has a cylindrical outer shape and includes a stator winding 2d wound around the tooth portion 2h. It has a so-called internal magnet arrangement type motor.
The stator winding 2d is wound around the stator 2c via an insulating layer 2f (see FIG. 1) made of a resin material. In order to detect the rotational position of the rotor 2a in the vicinity of the rotor 2a, there are three Hall ICs (rotational position detection) that are arranged every 60 ° in the rotational direction and detect the position of the rotor 2a electromagnetically. Elements) 10 to 12 are arranged. In the star-connected stator winding 2d (U-phase, V-phase, W-phase), the current controlled by the inverter circuit unit 3 in the current-carrying section with an electrical angle of 120 ° based on the position detection signals of the Hall ICs 10-12. Is supplied. As another method for detecting the rotational position, a sensorless method is adopted in which the rotor position is detected by extracting the induced electromotive force (back electromotive force) of the stator winding 2d as a logic signal through a filter. You can also.
Referring to FIG. 1 again, the body housing portion 6a and the handle housing portion 6b are made of a synthetic resin material molded integrally. The body housing portion 6a and the handle housing portion 6b are configured to be divided into two parts on the vertical plane passing through the rotation shaft 2e of the motor 2. At the time of assembly, a pair of housing members (the left or right side portion of the body housing portion 6a and the handle housing portion 6b) is prepared, and the stator of the motor 2 is previously placed on one housing member as shown in the partial cross-sectional view of FIG. 2c, the rotor 2a, etc. are assembled, and then the other housing member is overlapped, and both housing members are fastened by screwing or the like. A plurality of stator holding portions (rib portions) (not shown) formed by integral molding with the body housing portion 6a are formed on the inner wall of the housing portion facing the outer peripheral surface of the stator 2c. Thus, the motor 2 is gripped or clamped.
A cooling fan 24 is coaxially provided at the front end side of the motor 2, and an exhaust port (ventilation port) is formed in the body housing portion 6a in the vicinity of the cooling fan 24, although not shown. An intake port (ventilation port) 21 is formed at the rear end of the body housing portion 6a. A passage 23 extending from the intake port 21 to an exhaust port formed in the vicinity of the cooling fan 24 is a cooling air flow passage. To suppress the temperature rise of the semiconductor switching element 3a of the inverter circuit unit 3 and the temperature rise of the stator winding 2d of the motor 2. In the driver mode or the drill mode, depending on the load condition of the motor 2, a large current flows through the switching element 3 a and heat generation of the switching element 3 a increases, so that the inverter circuit unit 3 may be forcibly cooled by the cooling fan 24. is important.
The inverter circuit unit 3 has a disk-shaped circuit board and covers one end side (rear side) of the stator 2 c of the motor 2 entirely. On the other hand, a dust-proof cover 22 is provided on the other end side (front side) of the stator 2 c and covers the other end side surface of the stator 2 c, similarly to the inverter circuit unit 3. Both the inverter circuit unit 3 and the dustproof cover 22 together with the stator 2c form a dustproof structure (sealed structure) that closes or seals the rotor 2a. Thereby, the penetration | invasion of the dust to the motor 2 can be prevented.
A battery pack 30 serving as a driving power source for the motor 2 is detachably attached to the lower end portion of the handle housing portion 6b. A control circuit board 4 including a control unit 31 that controls the rotation of the motor 2 is provided above the battery pack 30 so as to extend in the front-rear and left-right directions.
A switch trigger 7 is disposed near the upper end of the handle housing portion 6b, and the trigger operation portion 7a of the switch trigger 7 protrudes from the handle housing portion 6b in a state of being biased by a spring force. When the operator pushes the trigger operation portion 7a backward, the trigger push-in amount (operation amount) can be adjusted and the rotation speed of the motor 2 can be controlled. According to the present embodiment, the trigger pushing amount by the switch trigger 7 is reflected in the PWM duty of the PWM drive signal that drives the semiconductor switching element 3a of the inverter circuit unit 3.
The battery pack 30 is electrically connected so as to supply drive power to the switch trigger 7 and the control circuit board 4 and further to supply drive power to the inverter circuit unit 3. As the secondary battery constituting the battery pack 30, a lithium ion battery is used, but a nickel cadmium battery or a nickel hydrogen battery may be used. Lithium ion batteries have the advantage that they have an energy density about three times that of nickel cadmium batteries and nickel metal hydride batteries, and are small and lightweight. The output voltage of the battery pack 30 is, for example, 18.0V.
Next, a functional block diagram of the electric power tool according to the embodiment of the present invention will be described with reference to FIG. The inverter circuit 13 is mainly configured by six switching elements Q1 to Q6 mounted on the inverter circuit unit 3 and connected in a three-phase bridge format. As the switching elements Q1 to Q6, insulated gate bipolar transistors (IGBTs) are used in this embodiment, but field effect transistors (MOSFETs) and bipolar transistors may be used. The gates of the six switching elements Q <b> 1 to Q <b> 6 that are bridge-connected are connected to a control signal output circuit 33 included in the control unit 31. The collectors or emitters of the switching elements Q1 to Q6 are connected to a star-connected stator winding 2d (windings: U, V, W). As a result, the six switching elements Q1 to Q6 perform switching operations according to the PWM drive signals H1 to H6 of the switching elements input from the control signal output circuit 33, and the DC voltage of the battery pack 30 applied to the inverter circuit 13 Is converted into three-phase (U-phase, V-phase, W-phase) drive voltages Vu, Vv, Vw, and three-phase AC power is supplied to the stator winding 2d (three-phase windings U, V, W) To do.
In FIG. 3, the control part 31 is comprised by the various circuits mounted in the control circuit board 4 (refer FIG. 1). The calculation unit 32 performs overall control of the driver drill 1 including rotation control of the motor 2. Although not shown, the calculation unit 32 is a CPU for outputting a drive signal based on a processing program and data, a ROM for storing a processing program and control data for executing a control flow as described later, and data. The microcomputer includes a RAM for temporarily storing, a timer for counting time, and the like, and executes various processes based on the processing program and data. The rotor position detection circuit 34 detects the rotation position of the rotor 2 a based on the output signals of the Hall ICs 10 to 12, and outputs the position information of the rotor 2 a to the calculation unit 32. The rotation speed detection circuit 35 detects the rotation speed of the motor 2 from the time interval of signals output from the Hall ICs 10 to 12 at regular intervals.
The power switch circuit 38 is a main switch for supplying power to the control unit 31, and the power from the battery pack 30 is supplied to the power voltage supply circuit 39 by turning on the power switch circuit 38. Normally, the on / off of the switch of the power supply voltage supply circuit 39 operates in conjunction with the switch trigger 7, but in this embodiment, the on / off can also be controlled by a control signal from the calculation unit 32. For this reason, a control signal line from the arithmetic unit 32 to the power switch circuit 38 is connected. The power supply voltage supply circuit 39 converts the voltage supplied from the battery pack 30 into a predetermined voltage (for example, 5 V) used by the control unit 31 and supplies the voltage to the calculation unit 32 and other electric circuits (not shown). To do.
The current detection circuit 36 detects the drive current of the motor 2 using the shunt resistor 18 and outputs the information to the calculation unit 32. The voltage detection circuit 37 measures the voltage value supplied from the battery pack 30 and outputs the voltage value to the calculation unit 32. The switch operation detection circuit 40 determines whether or not a trigger operation has been performed by the trigger operation unit 7 a of the switch trigger 7 and outputs it to the calculation unit 32. The applied voltage setting circuit 41 sets the PWM duty of the PWM signal corresponding to the output control signal generated in the switch trigger 7 in response to the trigger pressing amount by the trigger operation unit 7a of the switch trigger 7. Although not shown in FIG. 3, a rotation direction setting circuit for the motor 2 is provided to detect the forward rotation or reverse rotation operation by the forward / reverse switching lever 9 (see FIG. 1) and Output.
The calculation unit 32 creates an output drive signal to the control signal output circuit 33 based on the output information of the current detection circuit 36, the voltage detection circuit 37, the switch operation detection circuit 40, and the applied voltage setting circuit 41, and performs switching. The voltages Vu, Vv, and Vw applied to the motor 2 are controlled by controlling the PWM duty of the PWM drive signals of the elements Q1 to Q6. At this time, the motor 2 is rotated at the target rotational speed set by the speed mode switch 42. Further, based on information of a rotation direction setting circuit (not shown) and the rotor position detection circuit 34, the switching voltages Q1 to Q6 are switched in a predetermined order to apply the applied voltage Vu to the stator windings U, V, and W. , Vv, Vw are controlled to be supplied in a predetermined order, and thereby, the motor 2 is controlled to rotate in the rotational direction set by the forward / reverse switching lever 9.
The calculation unit 32 converts the three negative power supply side switching elements Q4, Q5, and Q6 among the switching drive signals (three-phase signals) for driving the gates of the six switching elements Q1 to Q6 to the PWM drive signal H4. Based on the output signal of the applied voltage setting circuit 41 that is supplied as H5 and H6 and responds to the trigger pressing amount of the trigger operation section 7a of the switch trigger 7 (see FIG. 1), the duty ratio (PWM) of the pulse width of the PWM drive signal The electric power to the motor 2 is adjusted by changing the duty), and the start-up and rotation speed of the motor 2 are controlled. Instead of supplying the PWM drive signals to the three switching elements Q4, Q5, Q6 on the negative power supply side, the drive signals H1-H3 of the switching elements Q1, Q2, Q3 on the positive power supply side are formed as PWM drive signals. However, as a result, the applied voltage supplied from the DC voltage of the battery pack 30 to the stator windings U, V, W can be controlled.
In addition, the arithmetic unit 32 turns on the three negative power supply side switching elements Q4, Q5, and Q6 and turns off the three positive power supply side switching elements Q1, Q2, and Q3 among the switching elements Q1 to Q6. By short-circuiting the stator winding, a path through which current during braking flows is formed, and kinetic energy during motor rotation is converted into electrical energy, and braking operation by short-circuit braking is performed.
With the above configuration, the control unit 31 outputs the PWM drive signals H1 to H6 from the control signal output circuit 33 to the inverter circuit 13, and alternately controls the switching of the switching elements Q1 to Q6, thereby generating a three-phase AC voltage. Control is performed so that the stator windings U, V, and W of the motor 2 are output. Further, the motor current of the motor 2 and the motor rotation speed (rotation speed) are controlled by adjusting the PWM duty of the PWM drive signals H1 to H6.
Next, the relationship between the decrease in the power supply voltage, the motor rotation speed, and the generated torque will be described with reference to FIG. FIG. 4 is a graph showing the relationship between the rotational speed of the motor and the load applied to the motor. The vertical axis represents the rotational speed (rpm) of the motor, and the horizontal axis represents the load torque (N · m). When the power supply voltage of the battery pack decreases, the rotational speed of the motor also decreases accordingly. When the power supply voltage, that is, the rotation speed of the motor 2 when the battery pack 30 is fully charged is N 01 , the maximum torque that can be tightened is T 1 , and the relationship between the rotation speed and the generated torque is a linear motor characteristic. m1. The motor characteristic m1 moves in the direction of the arrow 41 as the remaining battery level of the battery pack 30 decreases. When the voltage decreases, the motor characteristic m1 becomes a characteristic indicated by the motor characteristic m2. In other words, the use of the battery pack 30 voltage drops, the motor speed during no load is N 02, the maximum torque is T 2 capable tightening. As a result, if the “mode 3 target rotational speed” set by the speed mode changeover switch 42 is set to the rotational speed NT3 , the battery pack 30 with a low remaining battery level has the motor 2 at the target rotational speed. Will not be able to rotate.
FIG. 5 shows the relationship between the target rotational speed and the motor characteristic m3 in each mode when the remaining battery level of the battery pack 30 is reduced. As can be understood from this figure, when the remaining battery level is low, the motor characteristic m3 does not intersect with any of the target rotational speeds of modes 1 to 3, so that the motor is rotated at any target rotational speed of modes 1 to 3. I can't do that. For this reason, even if the operator switches the speed mode, there arises a problem that the rotational speed of the motor does not change.
Therefore, in this embodiment, as shown in FIG. 6, by making the target rotation speed of each mode variable according to the change of the power supply voltage, it is possible to appropriately switch the number of speed mode stages even if the power supply voltage changes. did. The purpose of constant speed control of power tools is to prevent a decrease in the number of revolutions at high loads and improve workability.Also, the speed mode switching is to perform fine control according to the work contents. In the embodiment, the speed mode can be switched even if the power supply voltage decreases. The degree to which the rotational speed is reduced in accordance with the reduction in the power supply voltage may be appropriately set according to the characteristics of the motor and the power tool and the intended use. For example, the battery pack 30 of 18.0 V specification is fully charged. When the target rotational speeds of modes 1, 2 and 3 at the time of charging (21.0 V) are 14000 rpm, 17500 rpm and 21000 rpm, respectively, when the voltage of the battery pack 30 drops to 16.0 V, the modes 1 and 2 3 target rotation speeds may be 10666 rpm, 13333 rpm, and 16000 rpm, respectively.
FIG. 7 is a graph showing the relationship between the motor characteristic m3 when the remaining battery level is low and the target rotational speed in each mode. As can be understood from this figure, when the remaining battery level is low, the motor characteristic m3 intersects with any of the target rotational speeds of modes 1 to 3, so that the motor can be rotated at the target rotational speed. It will be possible. In this way, the target rotation speed can be changed by switching the speed mode depending on the remaining battery voltage, eliminating the problem that the target rotation speed will not change due to fluctuations in the power supply voltage, and depending on the work contents. The rotation speed can be switched appropriately.
Next, the motor control procedure in the embodiment of the present invention will be described with reference to the flowchart of FIG. First, in step 81, it is determined whether or not the switch trigger 7 is turned on. If the switch trigger 7 remains off, it is determined whether or not a tact switch (not shown), which is the speed mode changeover switch 42, is turned on (step 91). 2 is switched (step 92). If it is not turned on, the process returns to step 81 (step 91).
When the switch trigger 7 is turned on in step 81, a signal to that effect is sent to the power switch circuit 38, and the power switch circuit 38 starts supplying the voltage from the battery pack 30 to the power voltage supply circuit 39. The power supply voltage supply circuit 39 generates a power supply voltage (for example, DC 5V) necessary for each element in the control unit 31 from the voltage of the battery pack 30 and starts supplying the power supply voltage to the arithmetic unit 32 and other elements. By supplying the power supply voltage, the control unit 31 including the calculation unit 32 is turned on.
Next, the calculating part 32 receives the output of the voltage detection circuit 37, and detects the voltage value of the battery pack 30 (step 82). This voltage is a voltage immediately before the rotation of the motor 2 is started, and is a power supply voltage when the motor 2 is stopped. Next, the calculating part 32 discriminate | determines the speed mode of the set motor 2 (step 83). The speed mode maintains the previous state unless it is changed. If the speed mode is not switched before the operator presses the trigger switch, the previously set speed mode is maintained. Next, the calculating part 32 sets a target rotation speed from the relationship shown in FIG. 6 based on the voltage value detected by the voltage detection circuit 37 (step 84). In order to set the target rotational speed, the relationship shown in FIG. 6 may be stored in advance in the storage means in the form of an equation or a data table. When the target rotation speed is set, the calculation unit 32 starts the motor 2 and accelerates the rotation of the motor 2 up to the set target rotation speed. Since the start-up control of the motor 2 can be performed by a known PWM control, a detailed description is omitted. Since the time required for the processing from step 81 to step 85 is only a few ms or less, the operator who operates the switch trigger 7 will not feel the time lag.
Next, it is detected whether or not the switch trigger 7 has been turned off by the operator (step 86). Since the operation is completed or stopped when it is turned off, the calculation unit 32 sends a control signal to the control signal output circuit 33 to control the drive power supplied to the motor 2 to 0, and the motor. 2 is stopped, and the process returns to step 81 (step 90). If the trigger remains on in step 86, the motor drive control is continued (step 87), and the calculation unit 32 detects the rotational speed of the motor 2 using the rotational speed detection circuit 35 (step 88). Next, the computing unit 32 obtains a deviation between the detected rotational speed and the target rotational speed, and performs feedback control (constant speed control) using the PID control so that the rotational speed of the motor becomes the target rotational speed (step 89). ) And return to Step 86.
As described above, in this embodiment, the target rotational speed is calculated on the basis of the speed mode and the power supply voltage value, and the constant speed control is performed so that the target rotational speed is obtained. As a result, even if the battery voltage changes, the number of speed mode steps can be appropriately switched.
Next, a motor control procedure based on the second embodiment will be described with reference to FIGS. In the first embodiment, each time the switch trigger 7 is pulled, the target rotational speed based on the power supply voltage value is set. However, in the second embodiment, without changing the target rotational frequency frequently, the power supply voltage is measured and the target speed is reset when the speed mode changeover switch 42 is switched. FIG. 9 illustrates the state of this control. In FIG. 9, the vertical axis represents the power supply voltage (voltage of the battery pack 30) and the target rotational speed (rpm) of the motor 2, and the horizontal axis represents time (sec). Further, on the lower side of the figure, the operation state of the switch trigger 7 (output of the switch operation detection circuit 40) and the output signal waveform of the speed changeover switch 42 are described corresponding to the graph.
In FIG. 9, when the switch trigger 7 is pulled and a plurality of operations are performed, the battery voltage gradually decreases due to a voltage drop. In this figure, the target rotational speed is set to mode 3, the operations 101, 102, and 103 are performed three times, the speed mode switch is then operated, and the operations 108 and 109 are performed twice. It shows a broken state. Here, it is assumed that after the operation 103, the operator operates the speed mode switch 42 to set the mode 3 to the mode 4, the mode 1, the mode 2, and the mode 3 again. Since the speed mode changeover switch 42 in this embodiment is realized by a toggle switch, the pulse signals 104 to 107 are sent to the calculation unit 32 each time the button is pressed. The computing unit 32 changes the speed mode based on the pulse signals 104 to 106 and switches the target rotational speed. When the speed modes 1, 2, and 3 are set, the voltage value of the battery pack 30 is measured, and the target rotational speed corresponding to the voltage value is set based on the correspondence relationship shown in FIG. Accordingly, the target rotational speed a4 set at the time of the arrow a2 at which the battery voltage is lowered is only the difference ΔN (= N 31 −N 33 ) compared to the target rotational speed a3 corresponding to the arrow at the high battery voltage a1. Lower. As described above, in this embodiment, the target rotational speed is changed according to the battery voltage when the speed mode is switched.
Next, the motor control procedure in the second embodiment of the present invention will be described with reference to the flowchart of FIG. In this flowchart, the same control parts as those in FIG. 8 are denoted by the same reference numerals. First, in step 81, it is determined whether or not the switch trigger 7 is turned on. If the switch trigger 7 remains off, it is determined whether or not a tact switch (not shown), which is one of the control buttons of the driver drill, has been turned on (step 91). Reads the speed mode stored in the calculation unit. (Step 93). If it is not turned on, the process returns to step 81 (step 91).
Next, the calculation unit 32 receives the output of the voltage detection circuit 37, detects the voltage value of the battery pack 30 (step 94), and based on the detected voltage value and the speed mode determined from the relationship of FIG. The target rotational speed is set (step 95), and the process returns to step 81. When the switch trigger 7 is turned on in step 81, the calculation unit 32 starts to start the motor 2 and accelerates the rotation of the motor 2 to the set target rotational speed. The subsequent control from step 86 to 90 is the same as the control from step 86 to 90 in FIG.
As described above, according to the control of the second embodiment, the target rotational speed is calculated based on the speed mode and the power supply voltage value. Therefore, the target rotational speed can be changed according to the change in the battery voltage. As a result, even if the battery voltage changes, it is possible to appropriately switch the number of speed mode stages. Further, since the target rotational speed is switched only when the speed mode is switched, a constant rotational speed control is always possible unless the speed mode is switched. This is because if the target rotation speed is changed every time the motor is started, the rotation speed is likely to be affected by fluctuations in the battery voltage, and the rotation speed may vary in each operation.
Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 11 is a graph showing the relationship between the target rotational speed of the motor and the output torque. In the conventional method of controlling the rotation of the motor with the PWM duty fixed, when the load such as the reaction force received from the tip tool increases and the current flowing through the motor increases, the current value becomes the current value as shown by the dotted line 111. The rotational speed of the motor decreases in inverse proportion. On the other hand, in the constant speed control method using the PID control indicated by the solid line 113, in order to rotate the motor at the target speed, the input value is controlled by the deviation between the output value and the target value, its integration, and differentiation. The three elements are used for feedback and control. By using PID control in this way, the motor speed is kept constant until the motor current reaches a certain current value I 04 , as at least in the flat portion indicated by the arrow 112. .
Next, the relationship between the deviation (proportional) gain, integral gain, differential gain, and power supply voltage in PID control will be described with reference to FIG. In this embodiment, the PWM duty is PID controlled to perform constant speed control, but the control gain of PID control is switched in conjunction with the magnitude of the voltage. FIG. 12 is a graph showing the interlocking state. Thus, the controllability of PID control can be improved by making each control gain variable according to the battery voltage.
Next, a motor control procedure in the third embodiment of the present invention will be described with reference to the flowchart of FIG. In this flowchart, the control is substantially the same as the flowchart shown in FIG. 10, and the same reference numerals are given to the same parts. The difference from the second embodiment is that step 96 is added. After setting the target rotational speed in accordance with the power supply voltage in step 95, the control gain for PID control is switched in accordance with the power supply voltage. I made it. In order to set the control gain, the relationship shown in FIG. 12 may be stored in advance in the storage means in the form of an expression or a data table.
According to the third embodiment described above, in addition to the second embodiment, the control gain is switched in conjunction with the magnitude of the voltage, so that the controllability of PID control can be improved.
As mentioned above, although demonstrated based on the Example which shows this invention, this invention is not limited to the above-mentioned Example, A various change is possible within the range which does not deviate from the meaning. For example, in the above-described embodiment, the brushless DC motor is used as an example of the motor. However, other types of motors may be used as long as the target rotational speed is set and controlled by a microcomputer or the like. It may be in the form.
1 Driver drill 2 Brushless DC motor
2a Rotor (rotor) 2b Permanent magnet
2c Stator (stator yoke) 2d Stator winding 2e Rotating shaft 2f Insulating layer 2h Teeth section 3 Inverter circuit section 3a Semiconductor switching element 4 Control circuit board 5 Torque setting dial 6 Housing
6a Body housing part 6b Handle housing part 7 Switch trigger 7a Trigger operation part 8 Spindle 9 Forward / reverse switching lever 10, 11, 12 Rotation position detecting element (Hall IC)
DESCRIPTION OF SYMBOLS 13 Inverter circuit 18 Chant resistance 21 Inlet 22 Dust-proof cover 23 Air flow path 24 Cooling fan 25 Power transmission part 26 Deceleration mechanism part 27 Clutch mechanism part
28 Chuck (tip tool mounting part) 30 Battery pack (lithium ion secondary battery)
Reference Signs List 31 Control Unit 32 Calculation Unit 33 Control Signal Output Circuit 34 Rotor Position Detection Circuit 35 Rotation Number Detection Circuit 36 Current Detection Circuit 37 Voltage Detection Circuit 38 Power Switch Circuit 39 Power Supply Voltage Supply Circuit 40 Switch Operation Detection Circuit
41 Applied voltage setting circuit 42 Speed mode changeover switch H1-H6 PWM drive signal Q1-Q6 Switching element U, V, W Three-phase stator winding
A drive circuit for supplying power from a power source to the motor;
In the electric tool having a control unit for providing a target rotational speed of a plurality of modes and rotating the motor at a target rotational speed of a set mode,
A voltage detection circuit for detecting a voltage value of the power supply;
The power tool characterized in that the target rotational speed is set based on the detected voltage value.
The electric tool includes a switch trigger for rotating the motor,
The control unit measures the voltage value after the switch trigger is turned on and before the motor rotates,
The power tool according to claim 1, wherein the target rotational speed is set based on the measured voltage value.
The electric tool has a changeover switch for setting the target rotational speed,
The power tool according to claim 1, wherein the control unit measures the voltage value when the target rotation speed is changed by the changeover switch.
The electric power tool according to any one of claims 1 to 3, wherein the target rotational speed is set so as to maintain a proportional relationship with the power supply voltage.
The drive circuit is an inverter circuit including a semiconductor switching element,
The said control part controls rotation of the said motor by controlling the PWM duty supplied to the said inverter circuit, The electric tool as described in any one of Claims 1-4 characterized by the above-mentioned.
6. The electric tool according to claim 5, wherein the control unit performs constant speed control so that the rotational speed of the motor becomes a target rotational speed by performing PID control on the PWM duty.
The power tool according to claim 6, wherein the control unit changes a gain of the PID control based on a measured voltage value.
The power tool according to claim 7, wherein the control gain to be changed is increased or decreased in proportion to the power supply value.
The electric tool according to claim 1, wherein the motor is a brushless DC motor.
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