Power Tools

Abstract

To provide a power tool that stops driving of a motor before a shock due to operation of a clutch is generated to stabilize accuracy of tightening torque.SOLUTION: A power tool includes: a motor; a tip tool driven by the motor; and a clutch part provided in a rotation force transmission path of the motor and the tip tool. The clutch part is configured to include a ring gear 41 and a pin 51 and has a claw part 43 that moderates torque variation. The claw part 43 has a shape that changes into a ridge shape and a valley shape. A control unit detects a current of the motor and controls the motor to decrease the voltage or the rotation number thereof when the pin 51 runs on the claw part 43.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a power tool that can perform tightening at a set torque by using a clutch mechanism. [Background technology]

[0002] Driver drills as shown in Patent Document 1 are widely used as power tools for tightening screws and the like. Driver drills transmit the rotational force of a motor through a reduction mechanism and a clutch mechanism to rotate a tool holder such as a chuck. The clutch mechanism cuts off the transmission of power when a predetermined tightening torque is reached. In Patent Document 1, a so-called mechanical clutch is used as the clutch mechanism. This is a clutch mechanism in which a plurality of pins are brought into contact with a plurality of claws extending in the axial direction formed on the front end surface of the ring gear of the planetary gear reduction mechanism, and the clutch acts as a clutch when the engagement state is released. The plurality of pins are fixed to a clutch plate that is provided so as to be non-rotatable and axially movable with respect to the gear case, and the clutch plate is constantly biased toward the ring gear by a coil spring. The biasing force of the coil spring can be adjusted by turning a rotary dial, and the magnitude of the tightening torque when the clutch operates is set by this adjustment. On the other hand, driver drills have a "drill mode" in which the compression amount of the coil spring is maximized so that the engagement state between the clutch claw and the ball cannot be released, thereby restricting the operation of the clutch mechanism. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2011-194485 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional power tool described in Patent Document 1, the ring gear and the pin collide at high speed when the clutch is activated, so the accuracy of the tightening torque is not stable. Furthermore, the tightening torque is not stable depending on the number of revolutions of the motor when the clutch is in operation and the operation time or number of times the clutch is in operation.

[0005] The present invention has been made in view of the above-mentioned background, and an object of the present invention is to provide a power tool that stabilizes the accuracy of the tightening torque. Another object of the present invention is to provide a power tool that is provided with a slow-acting portion in the clutch mechanism that makes the change in torque gentler, thereby making it possible to accurately detect the state immediately before the clutch is actuated. It is still another object of the present invention to provide a power tool which facilitates control of motor rotation when the clutch is in operation. It is still another object of the present invention to provide a power tool in which the voltage or rotation speed is reduced when the pin of the clutch mechanism rides over the claw portion or when the cam mechanism of the clutch mechanism is operating. It is still another object of the present invention to provide a power tool having a clutch mechanism in which, when the clutch is actuated, the claws of the ring gear ride over the pin only once. [Means for solving the problem]

[0006] Representative features of the invention disclosed in this application are as follows. According to one aspect of the present invention, a power tool is provided that includes a motor, a tool bit driven by the motor, and a clutch unit provided in a rotational force transmission path between the motor and the tool bit, the clutch unit having a slow-motion unit that smooths changes in torque. The slow-motion unit includes a ring gear and a pin, the ring gear has a sliding surface that contacts the pin, and the pin is movable along the sliding surface. The sliding surface is formed to include a clutch cam that changes in a mountain-like and a valley-like shape in the direction of the rotation axis.

[0007] According to another feature of the present invention, the ring gear has a shape in which a cylindrical portion and a sliding surface formed in a mountain shape extending forward from the cylindrical portion are connected, and the sliding surface has a cross section perpendicular to the rotation axis and is formed so that the cross section moves back and forth in the circumferential direction. Here, it is preferable that the amount of change in the rotation axis direction of the pin along the sliding surface that changes into a mountain shape and a valley shape is equal to or greater than the thickness of the pin. A plurality of pins are provided, and the number of mountain-shaped and valley-shaped portions is the same as the number of pins.

[0008] According to yet another feature of the present invention, the slow-moving unit includes two ring gears movable by a predetermined relative angle via a cam mechanism, a plurality of claws formed on the front side of one of the ring gears, a plurality of pins engaging with the claws, a thrust plate for holding the pins, and a spring for biasing the thrust plate toward the ring gear. When torque from the motor is applied, the ring gear moves the pins forward while compressing the spring by the cam mechanism. The power tool also includes a control unit for controlling the rotation of the motor and a current detection unit for detecting the current of the motor, and the control unit reduces the voltage or rotation speed of the motor based on the detection result of the current detection unit. The control unit controls the motor to reduce the voltage or rotation speed when the pins are climbing up the clutch cam. For example, the control unit reduces the current value to zero or a value close to zero while the pins are climbing up the clutch cam, and returns the current to the original value or a sufficiently high value after a first predetermined time has elapsed, and stops the rotation of the motor after a second predetermined time has elapsed after the current is returned. Effect of the Invention

[0009] According to the present invention, it is possible to provide a power tool capable of stabilizing the accuracy of the tightening torque. It is also possible to provide a power tool that is capable of detecting the operation of the clutch with high accuracy. It is also possible to provide a power tool in which the rotation of the motor can be easily controlled when the clutch is in operation. It is also possible to provide a power tool in which the voltage or motor rotation speed is reduced when the pin of the clutch mechanism rides on the claw portion or when the cam mechanism of the clutch mechanism is operating. [Brief description of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing an overall structure of a driver drill 1 according to an embodiment of the present invention. [Diagram 2] 2 is an enlarged cross-sectional view of the clutch mechanism 40 in FIG. 1 (when the clutch is not in operation). [Diagram 3] 2 is an enlarged cross-sectional view of the clutch mechanism 40 in FIG. 1 (when the clutch is in operation). [Figure 4] 1 is a block diagram showing a circuit configuration of a drive control system of a driver drill 1 according to an embodiment of the present invention. [Diagram 5] 4A to 4C are diagrams for explaining the operation of the ring gear 41 and pin 51 of the clutch mechanism 40. [Figure 6] 5 is a flowchart showing a tightening control procedure performed by a control unit of the driver drill 1 of the present embodiment. [Figure 7] FIG. 11 is a diagram showing the relationship between current, torque, and rotation speed during operation of the driver drill 1 of the present embodiment (when the bolt is being tightened before seating). [Figure 8] FIG. 4 is a diagram showing the relationship between current, torque, and rotation speed during operation of the driver drill 1 of the present embodiment (when tightening a seated bolt). [Figure 9] 11 is an enlarged cross-sectional view of a clutch mechanism 140 according to a second embodiment of the present invention. FIG. [Figure 10] 10A and 10B are cross-sectional and side views of the clutch mechanism 140 in FIG. 9, in which (A) shows a state at the time of low torque, and (B) shows a state at the time of high torque. [Figure 11] 10A to 10C are views of the first ring gear 141 in FIG. 9, in which (A) is a front view, (B) is a rear view, and (C) is a cross-sectional view of the AA portion in (B). [Figure 12] FIG. 10 is a side view of the second ring gear 145 of FIG. 9. [Figure 13]1A and 1B are diagrams showing a conventional clutch mechanism, in which (A) is a perspective view of a ring gear 241 and a pin 251 that constitute the clutch mechanism, and (B) is an enlarged view of the vicinity of a claw portion 243 of the ring gear 241. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLES

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same parts are given the same reference numerals, and repeated explanations will be omitted. In addition, in this specification, the front-rear and up-down directions will be described as the directions shown in the drawings.

[0012] FIG. 1 is a cross-sectional view showing the overall structure of a driver drill 1, which is a power tool according to an embodiment of the present invention. As shown in FIG. 1, a brushless DC motor 3 is housed in a body 2a of a housing 2 in the driver drill 1, and the motor 3 applies a rotational force to a tool tip (not shown), such as a driver or a drill, which is detachably held in a chuck (tool tip holder) 12 attached to a spindle (output shaft) 31, via a power transmission unit such as a reduction mechanism unit 20 for reducing the rotational force and a clutch mechanism unit 40. An inverter circuit board 6 for driving the motor 3 is provided on the rear end side of the motor 3 within the body 2a of the housing 2. The motor 3 is a so-called inner rotor type brushless DC motor, and a rotor 3a having a magnet 3b is attached to a rotating shaft 3e, and a stator 3c having a stator coil 3d is fixed to the housing 2 side. A known inverter circuit using a switching element 7 such as a FET (Field effect transistor) is used to supply a drive current to the stator coil 3d. A small cooling fan 17 is provided coaxially with the rotating shaft 3e on the front side of the motor 3. As the motor 3 rotates, the cooling fan 17 also rotates, and outside air is drawn in through the air intake 10 located at the rear of the housing 2. The outside air cools the switching element 7 and motor 3 by flowing around them, and is then discharged through an exhaust port (not shown) located on the side of the housing 2.

[0013] The clutch mechanism 40, which is disposed on the tip side of the body 2a, is provided in the rotational force transmission path from the motor 3 to the tool tip, and controls whether or not the rotational torque obtained at the output shaft of the reduction mechanism 20 is transmitted to the spindle 31 in response to the load of the spindle 31. As a result, if a desired tightening torque (load torque) is set in advance using the torque adjustment and mode switching dial 5, the clutch mechanism 40 has a function of cutting off the transmission of rotation from the reduction mechanism 20 to the spindle 31 by causing the output shaft to rotate freely when the rotational force of the output shaft of the reduction mechanism 20 reaches the set tightening torque. The reduction mechanism 20 is composed of, for example, a three-stage planetary gear reduction mechanism (first to third planetary gear units 21 to 23) that meshes with the sun gear 21a fixed to the rotating shaft 3e of the motor 3. The reduction mechanism 20 has a shift knob 15 for changing the gear ratio. The user can change the gear ratio in two stages, low speed and high speed, by manually switching the shift knob 15.

[0014] The handle portion 2b of the housing 2 is formed so that its longitudinal central axis extends in a direction substantially perpendicular to the rotation axis A1 of the body portion 2a. A trigger switch 13 is disposed at the upper end of the handle portion 2b, and a trigger operating portion 13a of the trigger switch 13 protrudes forward from the handle portion 2b when pressed by a spring force. A user can adjust the amount of trigger depression (operation amount) and control the rotation speed of the motor 3 by holding the handle portion 2b with one hand and pulling the trigger operating portion 13a backward with an index finger or the like. The rotation direction of the motor 3 can be switched by operating a forward / reverse switching lever 14.

[0015] A battery attachment section 2c is formed at the lower end of the handle section 2b, i.e., at a portion distant from the body section 2a. A battery 4 serving as a driving power source for the motor 3 is detachably attached to the battery attachment section 2c. The battery 4 supplies operating power to the trigger switch 13 and the control circuit section 9, and also supplies driving power for the motor 3 to the inverter circuit board 6. The secondary battery constituting the battery 4 may be, for example, a lithium ion battery, a nickel metal hydride battery, or a nickel cadmium battery. When removing the battery 4 from the state shown in FIG. 1, the latch buttons 4a on both the left and right sides are pressed while the battery 4 is moved forward relative to the power tool body.

[0016] A control circuit unit 9 for controlling the inverter circuit board 6 of the motor 3 is provided above the battery 4 so as to extend in the front-rear and left-right directions. A control panel 11 is provided above the control circuit unit 9. On the control panel 11, a battery remaining capacity display switch and a battery remaining capacity display lamp for displaying the remaining capacity of the battery 4 are arranged.

[0017] The body section 2a of the housing 2, together with the handle section 2b and the battery attachment section 2c, is manufactured by integral molding of a synthetic resin material, and is formed so as to be divided into two, left and right, by a vertical plane passing through the rotating shaft 3e of the motor 3. When assembling, a left member and a right member of the housing 2 are prepared, and the motor 3, the reduction mechanism section 20, the clutch mechanism section 40, etc. are assembled in advance into one of the housings 2 (for example, the left housing) as shown in the cross-sectional view of Fig. 1, and then the other housing 2 (for example, the right housing) is placed on top and fastened with a plurality of screws (not shown).

[0018] 2 is an enlarged cross-sectional view of the clutch mechanism 40 in FIG. 1. The reduction mechanism 20 is mainly composed of first to third planetary gear units 21 to 23 and first to third carrier units 24 to 26. The first planetary gear unit 21 has a sun gear 21a attached to the rotating shaft 3e of the motor 3 and a plurality of planetary gears that revolve between a ring gear 22b. The planetary gears of the first planetary gear unit 21 are held by the first carrier unit 24. A sun gear 24a is formed coaxially on the front side of the first carrier unit 24. The second planetary gear unit 22 has a sun gear 24a formed on the first carrier unit 24 and a plurality of planetary gears 22a that revolve between a ring gear 22b of the second planetary gear unit 22. In the third planetary gear portion 23, a plurality of planetary gears 23a revolve between a sun gear 25a formed on the second carrier portion 25 and a ring gear 41 of the third planetary gear portion 23. The third carrier portion 26 has a square hole 26a that engages with a square portion 31a provided in the spindle 31, and a driving force is transmitted from the third carrier portion to the spindle 31 by the engagement of the square portion 31a with the square hole 26a.

[0019] The clutch mechanism (clutch) 40 includes a ring gear 41 with a claw portion formed thereon, a pin 51 that abuts against the claw portion, and a gear case 50 that guides the tip of the pin 51 and has a plurality of axial through holes formed in the circumferential direction. The ring gear 41, which constitutes the third-stage planetary gear reduction mechanism, has a claw portion (clutch claw) (described later) on its front end surface, and three claw portions protruding forward in the direction of the rotation axis A1 are provided at equal intervals in the circumferential direction, and the three pins 51 come into contact with the front edge surface of the ring gear 41. The three pins 51 (only one pin is visible in the figure) are fixed to a thrust plate 53 that is non-rotatable with respect to the gear case 50 and axially movable. A compression coil spring 54 is disposed on the front side of the thrust plate 53, and the front side of the coil spring 54 is held by a nut 55 that is axially movable. The nut 55 is configured to rotate in synchronization with the rotation of the dial 5.

[0020] The inner wall of the nut 55 is formed with a threaded portion that can be screwed into a threaded portion provided on the outer periphery of the gear case 50, and the thrust plate 53 is a ring-shaped member that is continuous in the circumferential direction. The dial 5 and the thrust plate 53 are connected so that they cannot rotate relative to each other in the rotational direction, but can move relative to each other in the axial direction. Therefore, when the dial 5 is rotated, the nut 55 moves along the thread of the gear case 50 in a direction that compresses the coil spring 54. By moving the thrust plate 53 in the axial direction (front-rear direction), it is possible to adjust the strength of the rearward biasing force of the pin 51, which is biased rearward by the thrust plate 53. The position of the dial 5 in FIG. 2 is the state in which the coil spring 54 is most extended, and the torque at which the clutch mechanism operates is the smallest.

[0021] Due to the shape of the claw portion (see FIG. 5 described later) formed on the front end surface of ring gear 41 and the rear end portion of pin 51, when the torque transmitted to spindle 31 increases, the claw portion acts to push pin 51 forward. Then, by moving pin 51 axially forward against the biasing force of coil spring 54, the engagement between the claw portion and pin 51 is released, and rotation of ring gear 41 is permitted, thereby cutting off the transmission of rotational force from the reduction gear of reduction mechanism 20 to spindle 31. The state when this is cut off is shown in FIG.

[0022] As can be seen by comparing FIG. 3 with FIG. 2, the rotation of the ring gear 41 causes the position of the rear end of the pin 51 (contact position with the ring gear 41) to change forward. When the pin 51 is located forward, the coil spring 54 is compressed. The torque at the time when the top of the claw portion of the ring gear 41 and the pin 51 are released is the so-called tightening torque. The tightening torque can be adjusted by adjusting the compression amount of the coil spring 54. When a drill bit is attached as the tip tool to perform drilling work, it is necessary to transmit a large tightening torque to the spindle 31. However, if the thrust plate 53 is rotated by the dial 5 until the coil spring 54 is sufficiently compressed, the axial movement of the pin 51 is prevented, and therefore the operation of the clutch mechanism 40 can be suppressed, thereby realizing the so-called "drill mode."

[0023] Next, the configuration and operation of the drive control system of the motor 3 will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the configuration of the drive control system of the motor 3. The stator 3c of the motor 3 has a stator coil 3d consisting of star-connected three-phase stator windings U, V, and W, and is provided with three rotational position detection elements (Hall ICs) 8 arranged at predetermined intervals in the circumferential direction, for example, at intervals of 60°, in order to detect the rotational position of the magnet 3b. The direction and time of current flow to the stator windings U, V, and W are controlled based on position detection signals from these rotational position detection elements 8, and the motor 3 rotates.

[0024] The electronic elements mounted on the inverter circuit board 6 include six switching elements 7 (Q1 to Q6) connected in a three-phase bridge configuration. These are controlled by the calculation unit 81 controlling the control signal output circuit 82, one of the control means mounted on the control circuit unit 9. The control signal output circuit 82 supplies PWM signals to the switching elements Q1 to Q6 based on the output from the calculation unit 81. The power supplied to each coil U, V, and W can be adjusted by controlling the pulse width of the PWM signal to control the number of rotations of the motor 3 in the set rotation direction. Although not shown, the calculation unit 81 includes a CPU for outputting a drive signal based on a processing program and data, a ROM for storing a program corresponding to a flowchart described later and control data, a RAM for temporarily storing data, and a microcomputer with a built-in timer, etc. The switch operation detection circuit 90 outputs an ON signal to the calculation unit 81 when the trigger switch 13 is operated even slightly. The applied voltage setting circuit 91 outputs a detection signal proportional to the operation amount (stroke) of the trigger switch 13 to the calculation unit 81. The calculation unit 81 sets the pulse width (duty ratio) of the PWM signal based on the amount of operation of the trigger switch 13, thereby controlling the start / stop and rotation speed of the motor 3.

[0025] The rotor position detection circuit 83 synthesizes the output signals of the three rotational position detection elements 8 to generate a position detection pulse and outputs it to the calculation unit 81. The rotation speed detection circuit 84 is a circuit that detects the rotation speed of the motor based on the number of detection signals from the rotor position detection circuit 83 counted within a unit time. The current detection circuit 86 is a voltage detection means that detects the current flowing through the motor 3 by measuring the voltage across the shunt resistor 85, and the detection value is input to the calculation unit 81. In other words, the shunt resistor 85 and the current detection circuit 86 constitute the current detection unit. The voltage detection circuit 87 is a circuit that measures the voltage of the battery 4, and the output of the voltage detection circuit 87 is input to the microcomputer. The power switch circuit 88 is turned on by the first pulling operation of the trigger switch 13, and instructs the power supply voltage supply circuit 89 to generate a reference voltage (3.3V or 5V) for operating the calculation unit 81 from the voltage supplied from the battery 4 and supply it to the calculation unit. Once the supply of the reference voltage from the power supply switch circuit 88 is started, the microcomputer of the calculation unit 81 outputs a hold signal 81a to maintain the supply of the reference voltage from the power supply switch circuit 88 until the microcomputer is shut down.

[0026] Next, the operation of the ring gear 41 and the pin 51 of the clutch mechanism 40 will be described with reference to FIG. 5. Before describing the structure of the ring gear 41 and the pin 51 of this embodiment, the shape of the ring gear 241 and the pin 251 of a conventional driver drill will be described with reference to FIG. 13. The conventional ring gear 241 has a cylindrical portion 242 with a gear (not shown) formed on the inside, and the front side of the cylindrical portion 242 is formed as an annular flat surface 244. Three claw portions 243 protruding forward in the rotation axis direction A1 are formed at three points in the circumferential direction of the flat surface 244. The tip portions 251a of the three pins 251 abut against the flat surface 244. The tip portions 251a of the pins 251 are formed in a hemispherical shape. When the planetary gear (not shown) arranged inside the ring gear 241 rotates, a rotating torque T is applied to the ring gear 241, but the rotation of the ring gear 241 is prevented by contact friction with the pin 251. When the reaction force from the tool tip against the tightening force becomes large, the reaction force exceeds the static friction force between the flat surface 244 of the ring gear 241 and the tip 251a of the pin 251. As a result, the claws 243 of the ring gear 241 come into contact with the pin 251. Furthermore, when the reaction force from the tool tip becomes large, the pin 251 climbs the inclined surface 243b while compressing the coil spring (not shown). The force F2 is received by the ring gear 241 during the climbing process. When the ring gear 241 rotates and the pin 251 moves further from the position shown in FIG. 13(B), it reaches the apex 243a, which is the protruding apex of the claws 243. Then, the force received at that time is suddenly reduced from F2. The clutch torque is determined by the product of F2 and the arrangement radius of the claws provided on the ring gear (approximately the outer circumferential radius of the ring gear), and F2 is proportional to the inclination angle θ of the claws and the compression force F1 of the spring. Here, the easiest way to obtain a large clutch torque is to set θ to a large value, but as mentioned above, in the conventional structure, the claw portion 243 and the pin 251 collide repeatedly at high speed and are therefore prone to damage, so θ is generally set to about 30° to 40°. Thus, in the conventional clutch structure, there are significant restrictions on the setting of the inclination angle.

[0027] Returning to FIG. 5 again, in the driver drill 1 of this embodiment, the shape of the ring gear 41 is a major feature, and the claws 43 and pin 51 of the ring gear 41 form a slow-motion portion that smooths out the change in torque in the clutch portion. FIG. 5(A) shows a state (initial state) when no rotational force is acting on either the ring gear 41 or the pin 51. This state is when the motor 3 is stopped or is driven without load. FIGS. 5(A) to (E) show two views in the vertical direction, with the upper side being a side view of the ring gear 41 and the pin 51 and the lower side being a perspective view thereof, with the upper and lower sides corresponding to each other in each state in (A) to (E).

[0028] In FIG. 5(A), the ring gear 41 is composed of a cylindrical portion 42 with an internal gear (not shown) formed on the inside, and a claw portion 43 protruding forward (toward the pin 51) from the cylindrical portion 42. The claw portion 43 is a part called a clutch cam, so the ring gear 41 itself constitutes a clutch cam. The front surface of the claw portion 43 becomes a sliding surface with which the semispherical tip portion 51a of the pin 51 moves relatively while contacting it, and the portion located at the front side as viewed in the direction of the rotation axis A1 is the apex portion 44, and the portion located at the rear side is the valley portion 46. The apex portions 44 and the valley portions 46 are formed in three places, and the number of the apex portions 44 and the valley portions 46 is the same as the number of the pins 51. When the number of the pins 51 is large, the apex portions 44 and the valley portions 46 may be formed according to the number of the pins. The apex portions 44 and the valley portions 46 are connected to each other by an inclined portion 45, and the inclined portion 45 is inclined so that the axis position changes. Here, the inclined portion 45 near the top 44 is formed as an inclined portion 45a having a slightly convex inclined surface when viewed from the front side in the direction of the rotation axis A1, and the inclined portion 45 near the valley portion 46 is formed as an inclined portion 45b having a slightly concave inclined surface, and the inclined portion 45 is formed by combining these. 2 is preferably equal to or larger than the thickness (diameter) of the pin 51. For example, for a pin diameter of 5 mm, the height L 2= 9.6 mm. It is the angle θ of inclined surface 45a (see FIG. 13(b)) that affects the clutch torque, and this angle must be manufactured precisely to improve torque accuracy. On the other hand, the angle of large surface 45b close to the valley is determined by the diameter of claw portion 43 and the ring gear, and is not directly related to clutch torque, so it does not need to be manufactured precisely.

[0029] When the operator pulls the trigger operation part 13a of the driver drill 1 and the motor 3 starts to rotate, the ring gear 41 remains in the position shown in FIG. 5(A) and the spindle 31 rotates while the reaction force from the tool bit is small. Then, when the reaction force from the tool bit increases, the ring gear 41 rotates in the direction of the arrow 48, which is the opposite direction to the forward rotation direction of the chuck 12 (clockwise as viewed from the rear in FIG. 1), due to the structure of the planetary gear. The state in which the ring gear 41 starts to rotate is shown in FIG. 5(B). At this time, the pin 51 moves in the direction shown by the arrow 56 (forward) while compressing the coil spring 54 (see FIG. 3) forward of the rotation axis A1 due to the action of the inclined part 45. This forward movement of the pin 51 receives a reaction force from the coil spring 54, and the current flowing through the motor 3 increases significantly.

[0030] FIG. 5(B) shows the relative positions of the ring gear 41 and the pin 51 when the current value of the motor 3 reaches a predetermined threshold current (here, 23 A) (this current value will be described later in FIG. 7). When the ring gear 41 rotates further from the state of FIG. 5(B), it reaches a position just before the apex 44 of the claw portion 43 as shown in FIG. 5(C). Then, it reaches the apex 44 as shown in FIG. 5(D). Since the apex 44 is a surface perpendicular to the rotation axis A1, the contact friction between the pin 51 and the apex 44 in the rotation direction is greatly reduced compared to the state of FIG. 5(C). Then, when the pin 51 passes the apex 44 as shown in FIG. 5(E), the ring gear 41 rotates quickly, and the pin 51 moves so as to slide down the inclined portion 45 and moves relatively toward the next valley portion 46. The process from FIG. 5(A) to FIG. 5(E) is the state in which the clutch mechanism is activated.

[0031] FIG. 6 is a flow chart showing the tightening control procedure by the control unit of the driver drill 1 of this embodiment. The series of procedures shown in FIG. 6 can be executed in software by the microcomputer included in the calculation unit 81 executing a program stored in advance, and are automatically executed or started when the microcomputer is started, and are stopped when the microcomputer is shut down. First, the microcomputer included in the calculation unit 81 judges whether the trigger operation unit 13a is pulled and the trigger switch 13 is turned on (step 101). If the trigger switch 13 is not turned on in step 101, it waits until it is turned on, and if it is turned on, it starts driving the motor 3. The rotation control of the motor 3 by the calculation unit 81 is controlled by the microcomputer according to the pulling amount of the trigger operation unit 13a. Next, the microcomputer of the calculation unit 81 detects the current value (here, the current value input to the inverter circuit 18) flowing through the motor 3 from the output of the current detection circuit 86 (step 103), and judges whether the current value exceeds a predetermined threshold current Is for a predetermined time (for example, 3 milliseconds) or more (step 104).

[0032] If NO in step 104, the process returns to step 102, and if YES, the microcomputer in the calculation unit 81 switches the output signal to the control signal output circuit 82 to reduce the PWM duty value (step 105). Next, the microcomputer waits for a first predetermined time (e.g., 0.5 seconds) while maintaining the PWM duty value reduced in step 105 (step 106). When the first predetermined time has elapsed in step 106, the microcomputer in the calculation unit 81 restores the PWM duty value to the value before it was reduced in step 105, thereby maintaining the rotation state of the motor 3 (step 107).

[0033] Next, the microcomputer of the calculation unit 81 measures the elapsed time after restoring the PWM duty value and judges whether a second predetermined time (e.g., 0.2 milliseconds) has elapsed (step 108), and if so, stops the rotation of the motor 3 (step 109). Next, the microcomputer of the calculation unit 81 judges whether the trigger switch 13 has been turned off by the operator releasing the trigger operation unit 13a (step 110), and if not, returns to step 109 and maintains the stopped state of the motor 3. If the operator releases the trigger operation unit 13a in step 110, returns to step 101.

[0034] 6, in this embodiment, the state in which the pin 51 passes through the inclined portion 45b of the claw portion 43 is determined based on the detection result of the current detection circuit 86 that detects the current flowing through the motor 3 as in step 104, and the PWM duty value of the motor 3 is reduced for a first predetermined time after the detection. Also, after the first predetermined time has elapsed, the motor 3 is stopped after a second predetermined time has elapsed at a predetermined PWM duty value.

[0035] Next, the relationship between the current, torque, and rotation speed of the driver drill 1 during control according to the flowchart of FIG. 6 will be described with reference to FIG. 7. The horizontal axis of FIG. 7 indicates the time (unit: seconds) that has elapsed since the trigger was pulled at time 0, and the current 111, the torque 112 generated by the motor 3, and the rotation speed 113 of the motor 3 are illustrated on a common horizontal axis. The current 111 is a current value detected by the current detection circuit 86. When the operator pulls the trigger operation part 13a at time t=0, the motor 3 starts, and duty control is performed so that the current value rises as indicated by the arrow 111a. Note that, although the actual current value 111 is a large starting current, in order to simplify the explanation, the starting current is ignored and the current value 111 is illustrated as having an ideal upward trend. When time t=0.9 seconds is reached, the rotation speed 113 of the motor 3 reaches 14,500 rpm set as the target rotation speed, and the rotation speed is maintained. The current value 111 at this time rises to a predetermined threshold voltage I S(23 A in this case). At this time, the bolt is in a state before it is seated, and the torque 112 applied to the bolt is close to 0, as indicated by the arrow 112a. As the bolt rotates in this manner, the bolt (not shown) is seated at approximately time t = 1.74 seconds, and the reaction force from the tool bit suddenly increases, causing the predetermined threshold voltage I S At this point, the answer is YES in step 104 in FIG. 6, and the pin 51 is in the position shown in FIG. 5(B).

[0036] Looking at the change in current 111 indicated by arrow 111c, the current value rises in a quadratic curve. This is because, in the process from Figure 5(A) to (B), pin 51 moves forward in the direction of rotation axis A1 along inclined portion 45, causing a sudden increase in the reaction force applied to motor 3. At this time, torque 112 generated in the output shaft rises suddenly as indicated by arrow 112b to 112c. Furthermore, because the reaction force applied to motor 3 increases suddenly, the rotation speed of motor 3 drops suddenly from arrow 113c to 113d.

[0037] The current 111 is maintained at almost zero between the arrows 111d and 111e. Here, due to the PWM control, the duty ratio is set to about 1% to reduce the output torque of the motor 3 to near 0, but the rotation of the motor 3 may be stopped so that the current 111 becomes 0. The torque 112 at this time drops sharply from the arrows 112c to 112d, and then gradually decreases in the section from the arrows 112d to 112f. The gradual decrease is due to the presence of inertial energy of the motor 3 and the reduction mechanism 20. At this time, the relationship between the pin 51 and the ring gear 41 returns from the state shown in FIG. 5(B) to the state shown in FIG. 5(A) due to the force of the coil spring 54. The rotation speed of the motor 3 also drops sharply from the arrows 113d to 113e, and the rotation speed 113 rotates at an extremely low speed as shown from the arrows 113e to 113f due to the rotation control of the motor 3 with a duty ratio of 1%.

[0038] time t 2 After the specified time of 0.5 seconds has elapsed, the time t 3 (=time t 2+0.5), current 111 is again passed to motor 3, and current 111 is passed for a predetermined time (here, 0.2 seconds) with a predetermined duty ratio. In this way, until the bolt is seated, control is performed so that a higher rotational speed of motor 3 has the advantage of shortening the working time, and after the bolt is seated, the rotational speed is controlled to be slower than the original speed to further prevent collision between the inclined portion 45a of the claw and pin 51. Note that the "predetermined duty ratio" for controlling the rotation of motor 3 after the bolt is seated is preferably set lower than the original duty ratio before the bolt is seated. However, if it is set too low, sufficient motor torque will not be obtained for the claw portion 43 to overcome the pin 51. 3 From 4 It is desirable to set the duty ratio up to 111e at a value that ensures the above torque and provides a sufficiently low rotation speed that does not affect torque accuracy. When this control is performed, the current 111 rises sharply as shown by arrow 111e to 111f (the relationship between the pin 51 and the ring gear 41 changes from the state shown in FIG. 5(A) to the state shown in FIG. 5(B)), and then the pin 51 passes the position shown in FIG. 5(C) and reaches the top 44 of the ring gear 41. The torque 111 of the output shaft immediately after this state shown in FIG. 5(C) reaches its peak as shown by arrow 111g to 111h. After that, the pin 51 passes the top 44 of the ring gear 41 and changes to the state shown in FIG. 5(D) to FIG. 5(E), and during this time t 4 Since the current supply to the motor 3 stops at (step 109 in FIG. 6), the current 111 suddenly drops to the arrow 111h. In addition, the torque 112 of the output shaft drops from the arrow 112i (position in FIG. 5(D)) as shown by the arrow 112j (position in FIG. 5(E)), and thereafter the torque 112 becomes zero. After the pin 51 passes the top 44 of the ring gear 41, the rotation speed 113 of the motor 3 rises momentarily as shown by the arrow 113h, then drops as shown by the arrow 113i, and stops.

[0039] 7, the control when tightening an unseated bolt has been described, but the tightening control in this embodiment is similarly effective when tightening a seated bolt. Here, tightening a seated bolt refers to a case where a bolt that has already been tightened is retightened (re-tightened) or retightened for confirmation (tightening confirmation) with the driver drill 1.

[0040] 8 is a diagram showing the relationship between current, torque, and rotation speed of the driver drill 1 when tightening a bolt that has already been seated. When the operator presses the tool tip (not shown) of the driver drill 1 against the bolt or the like to be tightened and pulls the trigger operation part 13a at time t=0, the motor 3 starts. Then, since the object to be tightened is already seated, the torque 115 applied to the output shaft rises suddenly, and the current 114 also rises suddenly as indicated by the arrow 114a, reaching a value of 0 at time t 2 At time t , as shown by arrow 114b, the voltage exceeds a predetermined threshold voltage (23 A in this case). Then, the microcomputer of the calculation unit 81 reduces the duty ratio of the PWM control of the motor 3 between arrows 114c and 114d to about 1% in order to cut off the current to the motor 3 for a first predetermined time (0.5 seconds in this case). 3 At time t 2 When 0.5 seconds have passed since the time t, the microcomputer of the calculation unit 81 resumes control based on the original duty ratio to cause the current 114 to flow again to the motor 3, and causes the current 114 to flow for a predetermined time (here, 0.2 seconds). As a result, the current 114 rises sharply as indicated by arrows 114e and 114f. After that, the microcomputer 4 As a result, the current flowing through the motor 3 becomes zero, as indicated by the arrow 114g.

[0041] By carrying out the above-mentioned current control, the torque 115 of the output shaft changes as shown in the figure. At arrow 115a, the positional relationship between the ring gear 41 and the pin 51 is in the state shown in FIG. 5(A). Thereafter, at the position of arrow 115b, the ring gear 41 rotates to the position shown in FIG. 5(B). At the position of the pin 51 shown in FIG. 5(B), the current 114 of the motor 3 is temporarily reduced to substantially zero as shown by arrow 114c, so that the torque 115 applied to the output shaft decreases as shown by arrow 115c. At this time, the ring gear 41 returns from the state shown in FIG. 5(B) to the state shown in FIG. 5(A). After that, at time t 3 When the supply of current 114 is resumed at time t, torque 115 applied to the output shaft increases rapidly, and in the process from arrow 115d to arrow 115e, ring gear 41 moves from the position shown in FIG. 5(A) to the position shown in FIG. 5(C), and after passing arrow 115f, pin 51 reaches apex 44 (see FIG. 5) of ring gear 41. When pin 51 reaches apex 44 in the vicinity of arrow 115g, the frictional force between tip 51a of pin 51 and inclined portion 45 decreases significantly, and so output shaft torque 115 also decreases as shown by arrow 115h. After that, at time t 4 After the motor 3 is stopped at , the pin 51 slides down the inclined portion 45 toward the valley portion 46, and the torque 115 decreases as indicated by an arrow 115h. The position of the ring gear 41 at this time is shown in FIG. 5(E).

[0042] As described above, the current control method shown in the flow chart of FIG. 6, that is, the control method of detecting that the current has reached a predetermined threshold value, cutting off the current to the motor for a first predetermined time (or reducing it to almost zero), supplying current to the motor 3 at a predetermined duty ratio for a second predetermined time, and stopping the current supply to the motor 3 (fastening completed), is also effective for re-fastening a bolt that has already been seated. In this embodiment, a large mountain-shaped claw portion (slow-moving portion) 43 is formed on the ring gear 41, making it easy to detect changes in the current 111 as indicated by the arrow 111c, and then cutting off the current to the motor 3 for a first predetermined time after detecting that the current value has reached a predetermined threshold value. This makes it possible to appropriately control the current of the motor 3 during clutch operation while accurately identifying the timing at which the clutch operates, and to reliably fasten the fastening member with a set torque. It is preferable to set the second predetermined time to the time required for the claw portion 143 of the ring gear 41 to get over the pin 51 only once. This is because, as with conventional structures, when the bolt goes over the claws multiple times, even if the torque generated each time is the same, the bolt increases in proportion to the number of clutch operations. (After a certain number of times, the value becomes constant, but the clutch accuracy changes depending on the number of strikes. EXAMPLES

[0043] Next, a second embodiment of the present invention will be described with reference to Figures 9 and 10. In the first embodiment, in order to accurately detect the current increase state immediately before the clutch operates when controlling the current of the motor 3 immediately after the clutch is operated, a ring gear 41 (see Figure 5) having mountain-shaped claws 43 with gentle slopes as shown in Figure 5 is used instead of the conventional ring gear 241 (see Figure 13). The adoption of this ring gear 41 is based on the fact that the current increase state immediately before the clutch operates is detected accurately at time t 1 ~t 2Since this is to smooth out the current change in the cam mechanism, other configurations may be used as long as they produce similar current characteristics. Therefore, in the second embodiment, the ring gear is configured such that the member on the side that contacts pin 51 (first ring gear) and the member on the side on which the internal gear is formed (second ring gear) are separately configured to form first ring gear 141 and second ring gear 145, and these are connected by a cam mechanism using a cam ball.

[0044] FIG. 9 is a partial cross-sectional view of a ring gear mechanism using a cam mechanism. The ring gear mechanism is a mechanism (slow-motion part) that uses the output shaft 120 of the reduction mechanism as an input and the spindle 131 that holds the chuck as an output. The basic configuration is that a claw portion 143 is formed on a front flat surface 144 of a first ring gear 141, and a pin 151 abuts against the front flat surface 144, and the first ring gear 141 moves by a predetermined relative angle with respect to a second ring gear 145 via a cam mechanism. The shapes of the first ring gear 141 and the pin 151 that is biased toward the first ring gear 141 side are the same as the claw shape of the conventional ring gear 241 shown in FIG. 13. However, the first ring gear 141 cooperates with the second ring gear 145, which has an internal gear formed on the inside, to form a ring gear mechanism. First ring gear 141 and second ring gear 145 are connected by a cam mechanism using cam balls 149a and 149b, allowing relative movement in the rotational direction and in the direction of rotation axis A1.

[0045] The cam mechanism causes the second ring gear 145 to rotate in the opposite direction to the rotation direction of the spindle 131 as the torque from the tool tip increases with the rotation of the planetary gear 122. However, when a torque difference occurs between the first ring gear 141 and the second ring gear 145, the positions of the cam balls 149a and 149b move, causing the two members to rotate relative to each other, and a force that moves the first ring gear 141 forward of the rotation axis A1 is applied by the action of the cam mechanism. FIG. 9(A) shows the first ring gear 141 in the normal position on the rear side of the rotation axis A1. In this state, the coil spring 154 is extended, and the distance between the thrust plate 153 and the nut 155 corresponds to the set torque value. Three pins 251 are arranged at equal intervals in the circumferential direction on the rear side of the annular thrust plate 153. Pin 251 is held by a through hole (not visible in the figure) formed in gear case 150 for pin 251 so that it can move in the direction of rotation axis A1 but cannot rotate in the circumferential direction around rotation axis A1.

[0046] 9(B) shows the state in which the first ring gear 141 rotates slightly in the rotational direction and moves forward along the rotation axis A1. In this embodiment, the first ring gear 141 moves forward significantly, so that the pin 151 moves forward against the biasing force of the coil spring 154. Here, the claw height L of the claw portion 143 formed on the first ring gear 141 is 4 is the height L of the claw portion 43 shown in the first embodiment (FIG. 5). 2 However, the height L of the claw portion 143 is sufficiently low. 4 In addition, the movable distance L of the first ring gear 141 3 9(B), the position of pin 151 can move back and forth to the same extent as pin 51 in the first embodiment. After the engagement with claw portion 143 is released in this state, the position of first ring gear 141 remains as in FIG. 9(B), and the top of pin 151 moves toward the next claw portion 143.

[0047] FIG. 10 is a cross-sectional view and a side view of the clutch mechanism 140. FIG. 10(A) shows a state at the time of low torque, in which the reaction force received from the tool tip side is small and the torque from the motor 3 is small. The first ring gear 141 is formed with two sets of cam guides 142a, 142b formed in a substantially V-shape in side view. The second ring gear 145 is formed with two sets of cam grooves 147a, 147b so as to face these cam guides 142a, 142b. A cam ball 149a is disposed between the cam guides 142a and 147a, and a cam ball 149b is disposed between the cam guides 142b and 147b. In the state of FIG. 10(A), when the reaction force received from the tool tip side becomes large and the output torque of the motor 3 increases, the first ring gear 141 and the second ring gear 145 rotate relative to each other, resulting in the state of FIG. 10(B). As can be seen by comparing with FIG. 9, the position of second ring gear 145 in the direction of rotation axis A1 cannot be moved, so first ring gear 141 moves forward in the direction of rotation axis A1.

[0048] Fig. 11 is a diagram of the first ring gear 141 in Fig. 9, where (A) is a front view, (B) is a rear view, and (C) is an inner side view viewed from a vertical cross section. When viewed from the front in Fig. 11(A), three claws 143 are arranged at equal intervals in the circumferential direction. A flat surface 144 perpendicular to the rotation axis A1 is formed between adjacent claws 143. The flat surface 144 and the claws 143 are sliding surfaces with which the tip 151a of the pin 151 comes into contact.

[0049] FIG. 11(B) is a rear view of the first ring gear 141. Cam guides 142a and 142b with a rotation angle of 150 degrees are formed on the first ring gear 141. Insertion recesses 142c and 142d are formed near the circumferential center of each of the cam guides 142a and 142b to incorporate the cam balls 149a and 149b into the cam guides 142a and 142b. FIG. 11(C) is a cross-sectional view of part AA in FIG. 11(B), showing a vertical cross-sectional view of the first ring gear 141 and a view of one of the insides from the vertical cross-sectional view. The first ring gear 141 has cam guides 142a and 142b formed thereon instead of an internal gear formed on the inner circumference.

[0050] FIG. 12 is a side view of the second ring gear 145 of FIG. 9. The second ring gear 145 is a gear in which an internal gear (not visible in the figure) is formed on the inner part on the rear side indicated by the arrow 146. A cylindrical part is extended to the front side of the internal gear part of the second ring gear 145, and cam grooves 147a, 147b that are approximately V-shaped in side view are formed on the outer circumferential side. The outer circumferential surface 145c other than the cam grooves 147a, 147b has a flat shape. By arranging the cam balls 149a, 149b in the two cam grooves 147a, 147b, the position of the first ring gear 141 relative to the second ring gear 145 moves back and forth in the direction of the rotation axis A1 by a cam mechanism using the cam balls 149a, 149b. This change in position of first ring gear 141 varies depending on the magnitude of the reaction force received from the tool tip, and as the reaction force from pin 151 applied to claw portion 143 (see FIG. 11) increases, the relative rotation angle of first ring gear 141 and second ring gear 145 from the normal position increases. After the clutch mechanism operates and pin 151 moves over claw portion 143, when the PWM duty ratio is reduced to 1% as shown at 105 in FIG. 6 and the torque from the motor is reduced to approximately 0, the biasing force of coil spring 154 (see FIG. 9) causes first ring gear 141 and second ring gear 145 to return to their original positions shown in FIG. 9(A).

[0051] Although the present invention has been described above based on two embodiments, the present invention is not limited to the above-mentioned embodiments, and various modifications are possible within the scope of the present invention. For example, in the power tool of the present embodiment, the first to third planetary gear units 21 to 23 are used as the reduction mechanism 20, but the configuration of the reduction mechanism 20 is arbitrary, and the power may be transmitted from the rotating shaft 3e of the motor 3 to the reduction mechanism having the ring gear 41 by any mechanism. In addition, in the above-mentioned embodiment, the motor 3 is used as the power source, but the tool may use another driving source such as an air motor. [Explanation of symbols]

[0052] 1 Driver drill 2 Housing 2a (Housing) body 2b (Housing) Handle section 2c (Housing) Battery mounting section 3 Motor 3a Rotor 3b Magnet 3c Stator 3d Stator coil 3e Rotating shaft 4 Battery 4a Latch button 5 dial 6 inverter circuit board 7 switching element 8 Rotational position detection element 9 Control circuit section 10 Air intake 11 control panel 12 chuck 13 trigger switch 13a Trigger operation part 14 Forward / reverse switching lever 15 Shift knob 17 Cooling fan 18 Inverter circuit 19a, 19b Bearings 20 reduction mechanism section 21 first planetary gear section 21a sun gear 22 second planetary gear section 22a planetary gear 22b ring gear 23 3rd planetary gear section 23a Planetary gear 24 First carrier portion 24a Sun gear 25 Second carrier portion 25a Sun gear 26 Third carrier portion 26a Square hole 28 Shaft 29 Lock pin 30 Lock ring 31 spindle 31a square portion 37 ring gear 38 carrier 40 clutch mechanism 41 ring gear 42 cylindrical portion 43 Claw portion 44 (claw portion) top portion 45 (claw portion) inclined portion 45a (top side) inclined portion 45b (valley side) inclined portion 46 (claw) valley 47 (pin) normal position 50 gear case 51 pin 51a tip 53 thrust plate 54 coil spring 55 nut 81 calculation unit 82 Control signal output circuit 83 Rotor position detection circuit 84 Rotation speed detection circuit 85 Shunt resistor 86 Current detection circuit 87 Voltage detection circuit 88 Power switch circuit 89 Power supply voltage supply circuit 90 Switch operation detection circuit 91 Applied voltage setting circuit 111, 114 Current 112, 115 Torque 113, 116 motor speed 120 output shaft 121 bearing holder 122 planetary gear 123 shaft 124 planetary carrier 140 clutch mechanism 141 first ring gear 141c outer circumferential surface 141d Inner surface 142a, 142b Cam guide 142c, 142d recess 143 claw 144 flat surface 145 2nd ring gear 145a Front opening 145b Rear opening 145c outer circumferential surface 146 inner tooth region 147a, 147b cam groove 148a, 148b Cam ball insertion groove 149a, 149b Cam ball 150 Gear case 151 Pin 151a Tip 153 Thrust plate 154 Coil spring 155 Nut 174a, 174b Bearing 241 Ring gear 242 Cylindrical base portion 243 Claw 243a Top flat surface 243b, 243c Slanted surface 244 Flat surface 251 Pin 251a Tip

Claims

1. A motor; a reduction mechanism for reducing the rotational force of the motor; a tool holder driven by the motor via the reduction mechanism, the tool holder detachably holding a tool; a clutch mechanism provided in a rotational force transmission path between the motor and the tool bit, the clutch mechanism being configured such that when the rotational force of the output shaft of the reduction mechanism reaches a set tightening torque, the output shaft of the reduction mechanism rotates freely to interrupt the transmission of the rotational force from the reduction mechanism to the tool bit holder; a current detection unit that detects a current of the motor; A power tool having a control unit for controlling the motor, the control unit is configured to reduce a voltage or a rotation speed of the motor when detecting that a value of a current flowing through the motor has reached a predetermined threshold current from an output of the current detection unit; the threshold current is set such that a value of the current flowing through the motor reaches the threshold current before the output shaft of the reduction mechanism rotates idly in a state in which a rotational force is applied to the clutch mechanism, the clutch mechanism includes a rotatable ring gear having a clutch cam with a peak, a valley, and an inclined portion connecting the peak and the valley, and a plurality of pins movable along the clutch cam in a direction of a rotation axis of the ring gear, The control unit detects that the current value flowing through the motor reaches the threshold current when the multiple pins move along the inclined portion toward the top of the clutch cam, and reduces the voltage or rotation speed of the motor.

2. The power tool according to claim 1 , wherein the control unit reduces the voltage or the rotation speed of the motor to reduce the current value to zero or to a value close to zero.

3. The power tool described in claim 1, characterized in that when the control unit detects that the current value flowing through the motor has reached the threshold current, it reduces the voltage or rotation speed of the motor, and then increases the voltage or rotation speed of the motor before the multiple pins reach the top, so that the multiple pins reach the top in a state where the motor voltage or rotation speed is increased.

4. The power tool according to claim 3 , wherein the control unit stops the motor after a plurality of pins have passed over the top while the voltage or rotation speed of the motor is increased.

Images