JP2020023037A - Electric tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for controlling a tightening torque. A voltage detection unit 26 detects a voltage supplied to a motor 2. The impact mechanism 9 is arranged between the motor 2 and the output shaft 8, and uses the rotational force of the motor 2 to apply an intermittent rotational striking force to the output shaft 8. The rotation speed acquisition unit 19 acquires the rotation speed of the motor 2. The motor control unit 24 controls the power supply to the motor 2 so that the rotation speed of the motor becomes equal to or less than the predetermined rotation speed when the impact mechanism 9 starts applying the rotational impact force. The motor control unit 24 controls the power supply to the motor 2 according to the voltage detected by the voltage detection unit 26 so that the voltage integral value per unit time becomes constant. [Selection diagram] Fig. 2

Description

  The present disclosure relates to a power tool for tightening a screw member such as a bolt or a nut with an intermittent rotational impact force.

  The impact rotary tool tightens the screw member by the hammer rotating with the motor output intermittently hitting the anvil in the rotation direction. The impact rotary tool is used in an assembly factory or the like, and the tightening torque of the screw member needs to be accurately controlled to a value set by a user.

  The impact rotary tool is supplied with electric power by mounting a battery pack containing a rechargeable battery. If the motor speed cannot be kept constant due to a decrease in the battery voltage, it may be difficult to control the tightening torque. Patent Literature 1 discloses an electric tool including a transforming unit that increases a voltage input from a power supply unit and inputs the boosted voltage to a motor when the voltage of the power supply unit decreases.

JP 2014-172163 A

  In the impact rotary tool, after the rotation impact force is generated by the impact mechanism, it is necessary to maintain the motor rotation speed constant in order to manage the tightening torque with high accuracy. Therefore, a technique for maintaining a constant motor rotation speed with simple control is desired.

  The present disclosure has been made in view of such a situation, and an object of the present disclosure is to provide a technique for controlling a tightening torque.

  In order to solve the above problem, an electric tool according to an embodiment of the present disclosure has an output shaft to which a tip tool can be attached, a motor that drives the output shaft, and a voltage detection unit that detects a voltage supplied to the motor. An impact mechanism disposed between the motor and the output shaft to apply intermittent rotational impact to the output shaft using the rotational force of the motor, a rotational speed acquiring unit for acquiring the rotational speed of the motor, When the mechanism starts applying the rotary impact force, the motor control unit controls the power supply to the motor so that the rotation speed of the motor becomes equal to or less than a predetermined rotation speed, and according to the voltage detected by the voltage detection unit. And a motor control unit that controls power supply to the motor such that a voltage integrated value per unit time is constant.

  Note that any combination of the above-described components, and any conversion of the expression of the present disclosure between a method, an apparatus, a system, a computer program, and a recording medium on which the computer program is recorded are also effective as aspects of the present disclosure. is there.

  According to the present disclosure, it is possible to provide a technique for controlling the power supply to the motor such that the voltage integral value per unit time is constant, thereby maintaining the motor rotation speed constant.

It is a figure showing composition of a power tool concerning an embodiment. It is a figure showing the functional block of a power tool. FIG. 4 is a diagram illustrating an example of a discharge characteristic of a battery. It is a figure which shows a mode that a hammer hits an anvil in a rotation direction. It is a figure for explaining the impact behavior by a hammer. FIG. 4 is a diagram illustrating a voltage waveform applied to a motor.

  FIG. 1 shows an outline of a configuration of a power tool 1 according to an embodiment of the present disclosure. In the electric power tool 1, electric power is supplied by a battery 13 incorporated in a battery pack that is detachable from the tool body. The motor drive circuit 11 includes a switching element such as an FET (field effect transistor) or an IGBT (insulated gate bipolar transistor) to form an inverter circuit, and controls the motor 2 in accordance with a control signal supplied from the control unit 10. Rotate. The motor 2 drives an output shaft to which the tip tool is attached.

  The rotor position detector 18 detects the position of the rotor of the motor 2 and supplies a rotor position signal to the controller 10. In the embodiment, the rotor position detection unit 18 may be a magnetic rotary encoder that detects the rotation angle of the motor 2, a Hall element, or the like. The voltage detection unit 26 detects a voltage supplied to the motor 2 and supplies a voltage detection signal to the control unit 10. The impact detection unit 12 detects a rotary impact applied to the output shaft by the impact mechanism, and supplies an impact detection signal to the control unit 10.

  FIG. 2 shows functional blocks of the power tool according to the embodiment. The motor drive circuit 11 drives the motor 2, and the rotation output of the motor 2 is reduced by the speed reducer 3 and transmitted to the drive shaft 5. A hammer 6 is connected to the drive shaft 5 via a cam mechanism (not shown). The hammer 6 is urged by a spring 4 toward an anvil 7 having an output shaft 8. The output shaft 8 can be attached with a screw member to be tightened or a tip tool suitable for a working environment.

  As long as no load equal to or more than a predetermined value acts between the hammer 6 and the anvil 7, the hammer 6 and the anvil 7 are engaged in the rotational direction, and the hammer 6 transmits the rotation of the drive shaft 5 to the anvil 7. However, when a load equal to or more than a predetermined value acts between the hammer 6 and the anvil 7, the hammer 6 retreats against the spring 4 by the cam mechanism, and the engagement state between the hammer 6 and the anvil 7 is released. Thereafter, by the urging by the spring 4 and the guidance by the cam mechanism, the hammer 6 advances while rotating, and applies a rotational impact to the anvil 7. In the electric power tool 1, the spring 4, the drive shaft 5, the hammer 6, and the cam mechanism are arranged between the motor 2 and the output shaft 8, and are intermittently mounted on the anvil 7 and the output shaft 8 by using the rotating force of the motor 2. And an impact mechanism 9 for applying an effective rotary impact force.

  In the electric power tool 1, the components such as the control unit 10 and the setting unit 15 are realized by a microcomputer mounted on a control board. The control unit 10 includes a rotation speed acquisition unit 19, a rotation angle acquisition unit 20, a rotation speed acquisition unit 21, an energy calculation unit 22, a fastening torque calculation unit 23, a motor control unit 24, and a control signal output unit 25. It has a function of calculating the fastening torque and controlling the rotation of the motor 2 based on the calculated fastening torque.

  The subject of the power tool or method according to the present disclosure includes a computer. When the computer executes the program, the main function of the tool or the method according to the present disclosure is realized. The computer includes, as a main hardware configuration, a processor that operates according to a program. The type of the processor is not limited as long as the function can be realized by executing the program. The processor includes one or more electronic circuits including a semiconductor integrated circuit (IC) or an LSI (large scale integration). Here, the term is referred to as an IC or an LSI, but the term varies depending on the degree of integration, and may be called a system LSI, a VLSI (very large scale integration), or a USLI (ultra large scale integration). A field programmable gate array (FPGA), which is programmed after the manufacture of the LSI, or a reconfigurable logic device capable of reconfiguring junction relations inside the LSI or setting up circuit sections inside the LSI, may be used for the same purpose. Can be. The plurality of electronic circuits may be integrated on one chip, or may be provided on a plurality of chips. A plurality of chips may be integrated in one device, or may be provided in a plurality of devices. The program is recorded on a non-transitory recording medium such as a computer-readable ROM, an optical disk, and a hard disk drive. The program may be stored in a recording medium in advance, or may be supplied to the recording medium via a wide area communication network including the Internet or the like.

  The operation switch 16 is a trigger switch operated by a user. The motor control unit 24 controls on / off of the motor 2 by operating the operation switch 16, and sends a control signal for rotating the motor 2 at a rotation speed corresponding to the amount of pull-in of the operation switch 16 from the control signal output unit 25 to the motor drive. It is supplied to the circuit 11. The motor drive circuit 11 supplies a drive voltage to the motor 2 according to a control signal supplied from the control signal output unit 25, and rotates the motor 2.

  In the power tool 1, a usable range is set for the battery voltage of the battery 13. When the battery voltage falls below the stop voltage in the usable range, the motor control unit 24 determines a voltage drop abnormality and starts motor driving. Battery management is prohibited.

  FIG. 3 shows an example of the discharge characteristics of the battery 13. The battery 13 can supply a voltage of 24.9 V when fully charged, and supplies a rated voltage of about 21.6 V when the battery capacity decreases from the fully charged state. In this example, when the stop voltage is set to TEV and the battery voltage falls below the stop voltage TE, the motor control unit 24 prohibits motor drive.

  In the power tool 1, while no load equal to or greater than the predetermined value acts between the hammer 6 and the anvil 7, the motor control unit 24 rotates the motor 2 at a rotation speed corresponding to the amount of operation switch 16 pulled in. Thereafter, when the impact mechanism 9 starts applying the rotational impact force, the motor control unit 24 controls the power supply to the motor 2 so that the rotational speed of the motor 2 becomes a constant value that is equal to or less than a predetermined rotational speed. In the embodiment, the rotation speed acquisition unit 19 obtains the rotation speed of the motor 2 from the rotor position signal, and the motor control unit 24 supplies power to the motor 2 so that the rotation speed of the motor 2 becomes the rotation speed N. Control. By limiting the rotation speed N to a low value in advance, the motor control unit 24 can always control the rotation of the motor 2 at the rotation speed N in the usable range of the battery voltage.

  The impact detection unit 12 detects an impact applied to the anvil 7 and the output shaft 8 by the impact mechanism 9. For example, the impact detection unit 12 may include an impact sensor that detects an impact caused by the hammer 6 striking the anvil 7, and an amplifier that amplifies the output of the impact sensor and supplies the output to the control unit 10. For example, the shock sensor is a piezoelectric shock sensor that outputs a voltage signal corresponding to a shock, and the amplifier amplifies the output voltage signal and supplies the amplified voltage signal to the control unit 10. Note that the impact detection unit 12 may adopt another configuration, for example, a sound sensor that detects an impact applied to the anvil 7 by the impact mechanism 9 by detecting an impact sound.

  The rotor position detection unit 18 supplies a rotor position signal to the rotation angle acquisition unit 20. In the embodiment, the rotation angle acquisition unit 20 has a function of acquiring the rotation angle of the output shaft 8 from the rotor position signal. Here, the rotation angle acquisition unit 20 acquires an angle at which the output shaft 8 rotates for each impact by the impact mechanism 9. Hereinafter, the angle at which the output shaft 8 rotates by one impact is simply referred to as “output shaft rotation angle”.

  FIGS. 4A to 4C show how the hammer 6 applies a rotational impact to the anvil 7. The hammer 6 has a pair of hammer claws 6a, 6b standing upright from the front, and the anvil 7 has a pair of anvil claws 7a, 7b extending radially from the center. The anvil 7 is integral with the output shaft 8, and the output shaft 8 rotates together with the anvil 7.

FIG. 4A shows a state in which the hammer claw and the anvil claw are engaged in the circumferential direction. The hammer claws 6a and 6b engage with the anvil claws 7a and 7b, respectively, and apply a rotational force in a direction indicated by an arrow A.
FIG. 4B shows a state in which the engagement state between the hammer claw and the anvil claw has been released. When a load equal to or more than a predetermined value acts between the hammer 6 and the anvil 7 in the engaged state, the hammer 6 retreats with respect to the anvil 7 by a cam mechanism (not shown), and the engagement between the hammer claw 6a and the anvil claw 7a. The engagement state and the engagement state between the hammer claw 6b and the anvil claw 7b are released.
FIG. 4C shows a state where the hammer claw hits the anvil claw to rotate the anvil 7. When the engagement state between the hammer claws 6a, 6b and the anvil claws 7a, 7b is released, the hammer 6 advances while rotating in the direction indicated by the arrow A, and the hammer claws 6a, 6b respectively move the anvil claws 7b, 7b. Hit 7a. Due to the impact, the anvil 7 rotates by an angle θ formed by l1 and l2. At this time, the rotation angle of the hammer 6 becomes (π + θ).

FIGS. 5A to 5D show a positional relationship in which the hammer 6 and the anvil 7 are schematically deployed in the circumferential direction in order to explain the impact behavior of the hammer 6.
FIG. 5A shows a state in which the hammer claws 6a and 6b hit the anvil claws 7a and 7b, respectively. The hammer 6 is applied with a rotational force in a direction indicated by an arrow A, and is applied with a biasing force by a spring 4 in a forward direction (a direction toward the anvil 7).

  When the hammer claws 6a, 6b strike the anvil claws 7a, 7b, they move in the direction relatively away from the anvil claws 7a, 7b in the circumferential direction while being retracted by the cam mechanism under the reaction force of the collision (FIG. 5 ( b)). Thereafter, the hammer claws 6a and 6b move so as to get over the anvil claws 7a and 7b, respectively (see FIG. 5C). Advance toward anvil 7. Then, as shown in FIG. 5D, the hammer claws 6a and 6b strike the anvil claws 7b and 7a, respectively. During the tightening operation of the screw member, the above operation is repeated at a high speed, and the rotary impact force of the hammer 6 is repeatedly applied to the anvil 7.

The rotation angle acquisition unit 20 acquires the output shaft rotation angle θ per impact using the detection result by the impact detection unit 12 and the detection result by the rotor position detection unit 18. Specifically, the rotation angle acquisition unit 20 acquires the output shaft rotation angle θ by one impact from the motor rotation angle φ between impacts using the following (Equation 1). When the impact detection unit 12 detects the impact by the impact mechanism 9, the rotation angle acquisition unit 20 derives the output shaft rotation angle θ between the impacts from the rotor position signal at the timing when the impact is detected.
θ = (φ / η) −π (Equation 1)
Here, η indicates the reduction ratio by the reduction gear 3.

The rotation speed acquisition unit 21 acquires the impact speed ω between impacts using the detection result by the impact detection unit 12, the detection result by the rotor position detection unit 18, and information from a timer (not shown). The rotation speed acquisition unit 21 specifies the time between hits from the timer output and calculates the hit speed ω. When the moment of inertia of the anvil 7 and the output shaft 8 is J, the energy calculation unit 22 applies the moment of inertia to the anvil 7 and the output shaft 8 by one impact of the impact mechanism 9 using the following (Equation 2). The impact energy E is calculated.
E = (1/2) × J × ω ² (2)

The tightening torque calculating unit 23 calculates the tightening torque T based on the impact energy E calculated by the energy calculating unit 22 and the output shaft rotation angle θ acquired by the rotation angle acquiring unit 20 using the following (Equation 3). Is calculated.
T = E / θ (Equation 3)
The motor control unit 24 controls the rotation of the motor 2 based on the tightening torque T calculated by the tightening torque calculation unit 23, and specifically, automatically stops the rotation of the motor 2. Hereinafter, a control example of the automatic motor stop will be described.

  The user sets a target tightening torque value (hereinafter, also simply referred to as “target torque value”) corresponding to the work target in the power tool 1 before starting the work. The receiving unit 14 receives an operation input by the user and supplies the operation input to the setting unit 15. The receiving unit 14 has a wireless communication module, and the user may perform an operation input on the power tool 1 using a remote controller attached to the tool. In the power tool 1 of the embodiment, the user can select one of the target torque values of 30 steps. Note that operation buttons and a touch panel may be provided on the tool body, and the receiving unit 14 may receive an input of a target torque value from a user.

  When the receiving unit 14 receives the input of the target torque value, the setting unit 15 derives the number of shut-off hits and the predetermined torque value corresponding to the target torque value with reference to the storage contents of the number of shut-off hits storage unit 17. Are set in the control unit 10. The setting unit 15 supplies the number of shut-off hits and a predetermined torque value to the control unit 10, and the control unit 10 sets the shut-off hit number to a state that can be used for rotation control of the motor 2. Called processing.

  The shut-off hit number storage unit 17 stores, for each target torque value of 30 steps, the number of hits from when a predetermined torque value is reached to when the target torque value is reached. The number of shut-off hits storage unit 17 may be configured as a master table, and the storage content may not be updated.

  The motor control unit 24 controls the rotation of the motor 2 based on the tightening torque T calculated by the tightening torque calculation unit 23. Specifically, when the tightening torque T reaches a predetermined torque value, the motor control unit 24 counts the number of impacts detected by the impact detection unit 12, and when the counted number of impacts becomes the shut-off impact number, the motor control unit 24 Stop rotation. By such motor control, the power tool 1 controls the tightening torque with high accuracy.

  In the above shut-off control, the shut-off hit number storage unit 17 stores the shut-off hit number on the assumption that the motor rotation speed is a constant value (the rotation speed N). Therefore, the power tool 1 of the embodiment needs to rotate the motor 2 at a predetermined rotation speed N even when the supply voltage from the battery 13 fluctuates.

  As shown in FIG. 3, the battery 13 has a discharge characteristic in which the output voltage decreases as the remaining amount decreases. The motor control unit 24 of the embodiment has a function of controlling the power supply to the motor 2 according to the voltage detected by the voltage detection unit 26 so that the voltage integrated value per unit time is constant.

  FIG. 6A is a conceptual diagram of a voltage waveform applied to the motor 2 when the voltage detection unit 26 measures the full charge voltage. According to this voltage waveform, a full charge voltage of 24.9 V is applied to the motor 2 at a duty ratio of 50%.

  FIG. 6B is a conceptual diagram of a voltage waveform applied to the motor 2 when the rated voltage is measured by the voltage detection unit 26. According to this voltage waveform, a rated voltage of 21.6 V is applied to the motor 2 at a duty ratio of 57.6%.

6A and 6B, the voltage integral values per unit time are set equal. That is,
24.9 [V] × 50 [%] = 21.6 [V] × 57.6 [%]
Therefore, the voltage integral value applied to the motor 2 can be made equal between the two voltage waveforms. The control value storage unit 30 may hold a table in which a duty ratio according to the supply voltage is recorded. The motor control unit 24 reads a duty ratio corresponding to the voltage detected by the voltage detection unit 26 from the control value storage unit 30 and generates a control signal output from the control signal output unit 25 at the read duty ratio.

  As described above, the motor control unit 24 changes the duty ratio of the voltage supplied to the motor 2 in accordance with the change in the supply voltage to the motor 2, so that the motor rotation speed changes due to the change in the supply voltage of the motor 2. Avoid the situation. Thereby, the power tool 1 can manage the tightening torque with high accuracy.

  The motor control unit 24 adjusts the advance angle control of the motor 2 in accordance with the fluctuation of the supply voltage to the motor 2, so that the power supply to the motor 2 has a constant voltage integrated value per unit time. May be controlled as follows. The motor control unit 24 performs advance angle control for estimating a phase delay of the coil current and advancing the phase of the applied voltage. The control value storage unit 30 holds a table in which the advance amount according to the supply voltage is recorded, and the motor control unit 24 stores the advance amount according to the voltage detected by the voltage detection unit 26 as the control value. The control signal output from the control signal output unit 25 may be generated so as to be read out from the unit 30 and to have the read advance amount.

  The present disclosure has been described based on the embodiments. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to the combination of each component or each processing process, and that such modifications are also within the scope of the present disclosure. .

An overview of aspects of the present disclosure is as follows.
An electric power tool (1) according to an embodiment of the present disclosure includes an output shaft (8) to which a tip tool can be attached, a motor (2) for driving the output shaft (8), and a voltage supplied to the motor (2). A voltage detection unit (26) to be detected is disposed between the motor (2) and the output shaft (8), and the output shaft (8) is intermittently hit by rotation using the torque of the motor (2). An impact mechanism (9) for applying a force, a rotation speed acquisition unit (19) for obtaining the rotation speed of the motor (2), and when the impact mechanism starts to apply a rotational impact force, the rotation speed of the motor is reduced to a predetermined rotation speed. A motor control unit (24) that controls power supply to a motor as follows, and supplies power to the motor in accordance with a voltage detected by a voltage detection unit (26). A motor control unit (24) for controlling the integrated value to be constant.

  The motor control unit (24) may change the duty ratio of the voltage supplied to the motor according to the change in the voltage supplied to the motor. Further, the motor control unit (24) may adjust the advance angle control of the motor according to the fluctuation of the supply voltage to the motor.

DESCRIPTION OF SYMBOLS 1 ... Power tool, 2 ... Motor, 8 ... Output shaft, 9 ... Impact mechanism, 10 ... Control part, 11 ... Motor drive circuit, 13 ... Battery, 18 · · · Rotor position detection unit, 19 · · · rotation speed acquisition unit, 23 · · · tightening torque calculation unit, 24 · · · motor control unit, 25 · · · control signal output unit, 26 · · · voltage detection Unit, 30... Control value storage unit.

Claims (3)

An output shaft to which the accessory tool can be attached,
A motor for driving the output shaft;
A voltage detection unit that detects a voltage supplied to the motor,
An impact mechanism that is disposed between the motor and the output shaft, and that applies an intermittent rotational impact to the output shaft using the rotational force of the motor,
A rotation speed obtaining unit for obtaining the rotation speed of the motor,
When the impact mechanism starts to apply the rotational impact force, the motor control unit controls the power supply to the motor so that the rotation speed of the motor is equal to or less than a predetermined rotation speed, and is detected by the voltage detection unit. A motor control unit that controls power supply to the motor in accordance with the voltage to be applied so that a voltage integrated value per unit time is constant.
A power tool comprising: The motor control unit varies a duty ratio of a voltage supplied to the motor in accordance with a variation in a supply voltage to the motor.
The power tool according to claim 1, wherein: The motor control unit adjusts the advance angle control of the motor according to a change in a supply voltage to the motor,
The power tool according to claim 1 or 2, wherein:

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