Patent Grant
11440166
The present invention relates to an impact tool and, more particularly, to an impact tool in which a control method of a motor used as a driving source is improved.
A portable impact tool, especially, a cordless impact tool which is driven by the electric energy accumulated in a battery is widely used. In the impact tool where a tip tool such as a drill or a driver is rotationally driven by a motor to perform a required work, the battery is used to drive a brushless DC motor, as disclosed in JP2008-278633A, for example. The brushless DC motor refers to a DC motor which has no brush (brush for rectification). The brushless DC motor employs a coil (winding) at a stator side and a permanent magnet at a rotor side and has a configuration that power driven by an inverter is sequentially energized to a predetermined coil to rotate the rotor. The brushless DC motor has a high efficiency, as compared to a motor with a brush and is capable of obtaining a high output using a rechargeable secondary battery. Further, since the brushless DC motor includes a circuit on which a switching element for rotationally driving the motor is mounted, it is easy to achieve an advanced rotation control of the motor by an electronic control.
The brushless DC motor includes a rotor having a permanent magnet and a stator having multiple-phase armature windings (stator windings) such as three-phase windings. The brushless DC motor is mounted together with a position detecting element configured by a plurality of Hall ICs which detect a position of the rotor by detecting a magnetic force of the permanent magnet of the rotor and an inverter circuit which drives the rotor by switching DC voltage supplied from a battery pack, etc., using semiconductor switching elements such as FET (Field Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) and changing energization to the stator winding of each phase. A plurality of position detecting elements correspond to the multiple-phase armature windings and energization timing of the armature winding of each phase is set on the basis of position detection results of the rotor by each of the position detecting elements.
Now, a relationship between movement of a striking part of the impact tool including the hammer and anvil and increase/decrease of the motor current will be described with reference to
Explanation is made by referring to
By the way, recently, increase of the output of the impact tool has been achieved and therefore it is possible to obtain a high rotational speed and a high fastening torque while reducing the size of the tool. However, realizing the high fastening torque causes striking stronger than necessary to be applied when performing the first striking in a screw fastening work or the like. As a result, damage risk of screw becomes even higher. As a countermeasure, it is considered that the fastening work is performed in a state where the rotation speed of the motor is decreased in order to reduce the impact. However, in this case, the time required for the entire fastening becomes longer and therefore decrease in operation efficiency is caused.
The present invention has been made in view of the above background and an object thereof is to provide an impact tool which is capable of fastening a small screw or pan head screw, etc., at high speed with high accuracy.
Another object of the present invention is to provide an impact tool which is capable of preventing breakage of screw head during striking without decreasing the fastening efficiency.
Yet another object of the present invention is to provide an impact tool which is capable of fastening a self-drilling screw having a prepared hole function or a tapping screw with high efficiency.
Aspects of the present invention to be disclosed in the present application are as follows.
(1) An impact tool comprising:
a motor;
a trigger;
a controller configured to control driving power supplied to the motor using a semiconductor switching element according to an operation of the trigger; and
a striking mechanism configured to drive a tip tool continuously or intermittently by rotation force of the motor, the striking mechanism including a hammer and an anvil,
wherein the controller drives the semiconductor switching element at a high duty ratio when the trigger is manipulated, and
wherein the motor is driven so that the duty ratio is lowered before a first striking of the hammer on the anvil is performed and the first striking is performed at a low duty ratio lower than the high duty ratio.
(2) The impact tool according to (1), wherein switching from the high duty ratio to the low duty ratio is performed before engagement between the hammer and the anvil is released.
(3) The impact tool according to (1), wherein switching from the high duty ratio to the low duty ratio is performed before the hammer begins to retreat.
(4) The impact tool according to (1) to (3) further comprising a current detector configured to detect a current value of current flowing through the motor or the semiconductor switching element,
wherein the controller is controlled so that the duty ratio is switched from the high duty ratio to the low duty ratio when the current value exceeds a first threshold for a first time.
(5) The impact tool according to (1) to (4), wherein
the motor is a brushless DC motor, and
the brushless DC motor is driven by an inverter circuit using a plurality of semiconductor switching elements.
(6) The impact tool according to (4) or (5), wherein
the high duty ratio is set in the range of 80 to 100%, and
the low duty ratio is set to a value that is equal to or less than 60% of the high duty ratio set.
(7) The impact tool according to (4) or (5), wherein the controller stops the driving of the motor when the current value exceeds a second threshold.
(8) The impact tool according to (4) to (7), wherein
the controller is configured to perform:
an increasing process of continuously increasing the low duty ratio at a predetermined rate when the current value detected by the current detector is equal to or less than the first threshold after switching from the high duty ratio to the low duty ratio as long as the duty ratio after increase does not exceed the high duty ratio,
a returning process of returning the duty ratio to the low duty ratio again when the current value detected by the current detector exceeds the first threshold again, and
a repeating process of repeating the increasing process and the returning process.
(9) The impact tool according to (4) to (7), wherein
the low duty ratio is returned to the high duty ratio when the current value detected by the current detector is equal to or less than a third threshold that is sufficiently lower than the first threshold after switching to the low duty ratio, and
the motor is driven so that the duty ratio is switched to the low duty ratio from the high duty ratio before next striking of the hammer on the anvil is performed and the next striking is performed at the low duty ratio.
(10) A method of controlling an impact tool including a motor, a trigger, a semiconductor switch element which controls driving power supplied to the motor and a striking mechanism configured to drive a tip tool continuously or intermittently by rotation force of the motor, the striking mechanism including a hammer and an anvil, the method comprising:
driving the semiconductor switch element at a high duty ratio when the trigger is manipulated;
lowering the high duty ratio to a lower duty ratio before a first striking of the hammer on the anvil is performed; and
performing the first striking at the low duty ratio.
According to the invention described in (1), the controller is driven at a high duty ratio when the trigger is pulled but the striking is performed in a state where the duty ratio is switched to a low duty ratio just before the first striking. Accordingly, it is possible to effectively prevent the breakage of the screw head or screw groove or the damage of the member to be fastened without reducing the operating speed, even when a short screw or a self-drilling screw having a prepared hole function is used in an impact driver using a high-power motor. As a result, it is possible to employ a high-power motor and also it is possible to reduce power consumption of the motor. Further, it is possible to improve the reliability and life of the impact tool.
According to the invention described in (2), since switching of the duty ratio is performed before engagement between the hammer and the anvil is released, fastening is carried out at maximum speed until striking is performed and the duty ratio is reliably reduced during the striking, so that impact striking can be performed by a suitable striking force. Conventionally, the current is decreased immediately after the engagement is released. Thereafter, the hammer is already started to accelerate by the force of a spring even when the duty ratio is reduced and therefore the striking force of the first striking is substantially reduced. However, according to the invention described in (2), since switching of the duty ratio is performed before engagement between the hammer and the anvil is released, the first striking can be performed at a low duty ratio.
According to the invention described in (3), since switching of the duty ratio is performed before the hammer begins to retreat, it is possible to prevent reduction of the fastening speed due to reduction of the duty ratio. In this case, since the time until the engagement releasing is too short when the hammer begins to retreat and then the duty ratio is reduced, there is a possibility that the speed of the motor is not sufficiently reduced. However, according to the invention described in (3), it is possible to sufficiently reduce the speed of the motor by rapidly reducing the duty ratio.
According to the invention described in (4), since the controller is controlled so that the duty ratio is switched from a high duty ratio to a low duty ratio when the current value detected by the current detector exceeds a first threshold for the first time, it is possible to switch the duty ratio just before performing the striking without separately providing a special detection sensor.
According to the invention described in (5), since the brushless DC motor for driving an inverter circuit is used, it is possible to perform a delicate fastening control by the control of the duty ratio.
According to the invention described in (6), since the high duty ratio is set in the range of 80 to 100% and the low duty ratio is set to a value that is equal to or less than 60% of the high duty ratio set, it is possible to securely complete a fastening work at the specified torque without causing lack of fastening torque.
According to the invention described in (7), since the controller stops the driving of the motor when the current value exceeds the second threshold, it is possible to prevent insufficient fastening or excessive fastening.
According to the invention described in (8), since the duty ratio is gradually increased at a predetermined rate after the duty ratio is dropped to the low duty ratio, it is possible to perform a variation control of the duty ratio by a simple processing without tracking the peak value of the motor current after the duty ratio is dropped to the low duty ratio for the first time. Further, even the controller using a microcomputer with a low processing capacity can realize the processing of the present invention.
According to the invention described in (9), since the low duty ratio is returned to the high duty ratio again when the current value is equal to or less than a third threshold that is sufficiently lower than the first threshold after switching to the low duty ratio, it is possible to normally complete the fastening work even when the current value is temporarily increased due to some factors such as disturbance. Accordingly, it is possible to prevent the occurrence of insufficient fastening.
The foregoing and other objects and features of the present invention will be apparent from the detailed description below and accompanying drawings.
a-c are schematic views showing a relationship between movement of a striking part of the impact tool including a hammer and anvil and increase/decrease of the motor current.
Hereinafter, an illustrative embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, a front-rear direction and an upper-lower direction are referred to the directions indicated by arrows of
Between the rotor 3a and the bearing 19a, a sleeve 14 and the rotor fan 13 are mounted coaxially with the rotating shaft 12. The rotor 3a forms a magnetic path formed by a magnet 15. For example, the rotor 3a is configured by laminating four plate-shaped thin metal sheets which are formed with slot. The sleeve 14 is a connection member to allow the rotor fan 13 and the rotor 3a to rotate without idling and made from plastic, for example. As necessary, a balance correcting groove (not shown) is formed at an outer periphery of the sleeve 14. The rotor fan 13 is integrally formed by plastic molding, for example. The rotor fan is a so-called centrifugal fan which sucks air from an inner peripheral side at the rear and discharges the air radially outwardly at the front side. The rotor fan includes a plurality of blades extending radially from the periphery of a through-hole which the rotating shaft 12 passes through. A plastic spacer 35 is provided between the rotor 3a and the bearing 19b. The spacer 35 has an approximately cylindrical shape and sets a gap between the bearing 19b and the rotor 3a. This gap is intended to arrange the inverter circuit board 4 (see
A handle part 2b extends substantially at a right angle from and integrally with the main body 2a of the housing 2. A switch trigger (SW trigger) 6 is disposed on an upper side region of the handle part 2b. A switch board 7 is provided below the switch trigger 6. A forward/reverse switching lever 10 for switching the rotation direction of the motor 3 is provided above the switch trigger 6. A control circuit board 8 is accommodated in a lower side region of the handle part 2b. The control circuit board 8 has a function to control the speed of the motor 3 by an operation of pulling the switch trigger 6. The control circuit board 8 is electrically connected to the battery 9 and the switch trigger 6. The control circuit board 8 is connected to the inverter circuit board 4 via a signal line 11b. Below the handle part 2b, the battery 9 including a nickel-cadmium battery, a lithium-ion battery or the like is removably mounted. The battery 9 is packed with a plurality of secondary batteries such as lithium ion battery, for example. When charging the battery 9, the battery 9 is removed from the impact tool 1 and mounted on a dedicated charger (not shown).
The rotary striking mechanism 21 includes a planetary gear reduction mechanism 22, a spindle 27 and a hammer 24. A rear end of the rotary striking mechanism is held by a bearing 20 and a front end thereof is held by a metal 29. As the switch trigger 6 is pulled and thus the motor 3 is started, the motor 3 starts to rotate in a direction set by the forward/reverse switching lever 10. The rotating force of the motor 3 is decelerated by the planetary gear reduction mechanism 22 and transmitted to the spindle 27. Accordingly, the spindle 27 is rotationally driven in a predetermined speed. Here, the spindle 27 and the hammer 24 are connected to each other by a cam mechanism. The cam mechanism includes a V-shaped spindle cam groove 25 formed on an outer peripheral surface of the spindle 27, a hammer cam groove 28 formed on an inner peripheral surface of the hammer 24 and balls 26 engaged with these cam grooves 25, 28.
A spring 23 normally urges the hammer 24 forward. When stationary, the hammer 24 is located at a position spaced away from an end surface of the anvil 30 by engagement of the balls 26 and the cam grooves 25, 28. Convex portions (not shown) are symmetrically formed, respectively in two locations on the rotation planes of the hammer 24 and the anvil 30 which are opposed to each other. As the spindle 27 is rotationally driven, the rotation of the spindle is transmitted to the hammer 24 via the cam mechanism. At this time, the convex portion of the hammer 24 is engaged with the convex portion of the anvil 30 before the hammer 24 makes a half turn, thereby the anvil 30 is rotated. However, in a case where the relative rotation is generated between the spindle 27 and the hammer 24 by an engagement reaction force at that time, the hammer 24 begins to retreat toward the motor 3 while compressing the spring 23 along the spindle cam groove 25 of the cam mechanism.
As the convex portion of the hammer 24 gets beyond the convex portion of the anvil 30 by the retreating movement of the hammer 24 and thus engagement between these convex portions is released, the hammer 24 is rapidly accelerated in a rotation direction and also in a forward direction by the action of the cam mechanism and the elastic energy accumulated in the spring 23, in addition to the rotation force of the spindle 27. Further, the hammer 24 is moved in the forward direction by an urging force of the spring 23 and the convex portion of the hammer 24 is again engaged with the convex portion of the anvil 30. Thereby, the hammer starts to rotate integrally with the anvil. At this time, since a powerful rotational striking force is applied to the anvil 30, the rotational striking force is transmitted to a screw via a tip tool (not shown) mounted on the mounting hole 30a of the anvil 30. Thereafter, the same operation is repeatedly performed and thus the rotational striking force is intermittently and repeatedly transmitted from the tip tool to the screw. Thereby, the screw can be screwed into a member to be fastened (not shown) such as wood, for example.
Next, the inverter circuit board 4 according to the present embodiment will be described with reference to
Since the switching element 5 has a very thin thickness, the switching element 5 is mounted on the inverter circuit board 4 by SMT (Surface Mount Technology) in a state where the switching element is laid down on the board. Meanwhile, although not shown, it is desirable to coat a resin such as silicon to surround the entire six switching elements 5 of the inverter circuit board 4. The inverter circuit board 4 is a double-sided board. Electronic elements such as three position detection elements 33 (only two shown in (2) of
Next, a configuration and operation of a drive control system of the motor 3 will be described with reference to
The motor 3 is a so-called inner rotor type and includes the rotor 3a, three position detection elements 33 and the stator 3b. The rotor 3a is configured by embedding the magnet 15 (permanent magnet) having a pair of N-pole and S-pole. The position detection elements 33 are arranged at an angle of 60° to detect the rotation position of the rotor 3a. The stator 3b includes star-connected three-phase windings U, V W which are controlled at current energization interval of 120° electrical angle on the basis of position detection signals from the position detection elements 33. In the present embodiment, although the position detection of the rotor 3a is performed in an electromagnetic coupling manner using the position detection elements 33 such as Hall IC, a sensorless type may be employed in which the position of the rotor 3a is detected by extracting an induced electromotive force (back electromotive force) of the armature winding as logic signals via a filter.
An inverter circuit is configured by six FETs (hereinafter, simply referred to as “transistor”) Q1 to Q6 which are connected in three-phase bridge form and a flywheel diode (not shown). The inverter circuit is mounted on the inverter circuit board 4. A temperature detection element (thermistor) 34 is fixed to a position near the transistor on the inverter circuit board 4. Each gate of the six transistors Q1 to Q6 connected in the bridge type is connected to a control signal output circuit 48. Further, a source or drain of the six transistors Q1 to Q6 is connected to the star-connected armature windings U, V W. Thereby, the six transistors Q1 to Q6 perform a switching operation by a switching element driving signal which is outputted from the control signal output circuit 48. The six transistors Q1 to Q6 supply power to the armature windings U, V, W by using DC voltage of the battery 9 applied to the inverter circuit as the three-phase (U phase, V phase, W phase) AC voltages Vu, Vv, Vw.
An operation unit 40, a current detection circuit 41, a voltage detection circuit 42, an applied voltage setting circuit 43, a rotation direction setting circuit 44, a rotor position detection circuit 45, a rotation number detection circuit 46, a temperature detection circuit 47 and the control signal output circuit 48 are mounted on the control circuit board 8. Although not shown, the operation unit 40 is configured by a microcomputer which includes a CPU for outputting a drive signal based on a processing program and data, a ROM for storing a program or data corresponding to a flowchart (which will be described later), a RAM for temporarily storing data and a timer, etc. The current detection circuit 41 is a current detector for detecting current flowing through the motor 3 by measuring voltage across a shunt resistor 36 and the detected current is inputted to the operation unit 40. The voltage detection circuit 42 is a circuit for detecting battery voltage of the battery 9 and the detected voltage is inputted to the operation unit 40.
The applied voltage setting circuit 43 is a circuit for setting an applied voltage of the motor 3, that is, a duty ratio of PWM signal, in response to a movement stroke of the switch trigger 6. The rotation direction setting circuit 44 is a circuit for setting the rotation direction of the motor 3 by detecting an operation of forward rotation or reverse rotation by the forward/reverse switching lever 10 of the motor. The rotor position detection circuit 45 is a circuit for detecting positional relationship between the rotor 3a and the armature windings U, V W of the stator 3b based on output signals of the three position detection elements 33. The rotation number detection circuit 46 is a circuit for detecting the rotation number of the motor based on the number of the detection signals from the rotor position detection circuit 45 which is counted in unit time. The control signal output circuit 48 supplies PWM signal to the transistors Q1 to Q6 based on the output from the operation unit 40. The power supplied to each of the armature windings U, V W is adjusted by controlling a pulse width of the PWM signal and thus the rotation number of the motor 3 in the set rotation direction can be controlled.
Next, relationship among the motor current, the duty ratio of PWM drive signal and the fastening torque in the impact tool of the present embodiment will be described by referring to the graph shown in
In the present embodiment, the limit value of the duty ratio 52 in PWM (Pulse Width Modulation) control is decreased to 40% from 100% as in the time t1 of (2) of
Since the duty ratio is decreased to 40% at time t1 in this way, it is possible to perform a subsequent striking at a suitable strength. Plural times of striking are performed while the motor current 51 at this time is varied from an arrow 51d to an arrow 51h depending on the rotational position and longitudinal position of the hammer 24 (
Next, relationship among the motor current, the duty ratio of PWM drive signal and the fastening torque in the impact tool of fastening a long screw or a long self-drilling screw will be described by referring to
As described above, in the present embodiment, the duty ratio is switched to a low duty ratio of 40% before the first striking and then subsequent striking is performed, instead of continuously performing the striking at the duty ratio of 100%. In this way, striking is always performed at a low duty ratio. Accordingly, there is no case that the fastening torque abruptly exceeds a setting torque value TN by the first striking. As a result, it is possible to securely complete the fastening by plural times of striking. In addition, although the high duty ratio and the low duty ratio are set as a combination of 100% and 40% in the present embodiment, each duty ratio may be set as other combinations in such a way that the high duty ratio is set in the range of 80 to 100% and the low duty ratio is set to a value that is equal to or less than 60% of the high duty ratio set. For example, the high duty ratio and the low duty ratio may be set as a combination of 90% and 30%.
Next, a setting procedure of a duty ratio for the motor control when performing a fastening work by the impact tool 1 will be described by referring to the flowchart of
Next, the operation unit 40 determines whether or not the detected motor current value I is equal to or greater than the stop discrimination current threshold ISTOP (Step 78). When it is determined that the motor current value I is equal to or greater than the stop discrimination current threshold ISTOP, the operation unit 40 stops the motor in Step 79 and the control procedure returns to Step 71. When it is determined that the motor current value I is less than the stop discrimination current threshold ISTOP (Step 78), the control procedure returns to Step 73. By repeating the above-described processing, striking is carried out in such a way that rotation by a high duty ratio is performed until just before a first striking is performed and the duty ratio is switched to the low duty ratio just before less than one rotation from the start of the striking. Accordingly, it is possible to prevent breakage of the screw and also it is possible to securely perform the fastening at a fastening setting torque by plural times of striking. Further, since the motor 3 is driven so as not to generate torque higher than necessary at the time of striking, it is possible to significantly improve the durability of the electric tool even when using a high-power motor 3. Furthermore, since it is possible to reduce the power consumption of the motor 3 when performing the striking, it is possible to extend the life of the battery.
Next, a second embodiment of the present invention will be described with reference to
Now, relationship among the motor current, the duty ratio of PWM drive signal and the fastening torque in the impact tool of the second embodiment will be described by referring to
Now, relationship among the motor current, the duty ratio of PWM drive signal and the fastening torque in the impact tool of the second embodiment will be described by referring to
Next, a setting procedure of a duty ratio for the motor control when performing a fastening work in the second embodiment will be described by referring to the flowchart of
Next, the operation unit 40 sets the PWM duty value according to the amount of operation of the switch trigger 6 that is detected (Step 115). Here, the PWM duty value according to the amount of operation can be set to (Maximum PWM duty value)×(amount of operation (%)), for example. Next, the operation unit 40 detects the motor current value I using the output of the current detection circuit 41 (Step 116). Next, the operation unit 40 determines whether or not the setting value (upper limit value) of the PWM duty ratio is set to 100% and the detected motor current value I is equal to or greater than the operation discrimination current threshold I1 (Step 117). Here, when it is determined that the motor current value I is equal to or greater than the operation discrimination current threshold I1, a power-down control flag is set (Step 126), the maximum value of the PWM duty ratio is set to 40% (Step 127) and the control procedure proceeds to Step 122. Here, the power-down control flag is a control flag that is turned on when the motor current value I is less than the operation discrimination current threshold I1. The power-down control flag is used for the execution of a computer program by a microcomputer included in the operation unit 40. When it is determined in Step 117 that the motor current value I is less than the operation discrimination current threshold I1, the power-down control flag is checked and it is determined whether the flag is already set or not (Step 118). When the power-down control flag is detected, 0.1% is added to a value of PWM duty ratio that is set in a previous stage (Step 119) and it is determined whether the present value of the PWM duty ratio is 100% or not (Step 120). Here, when it is determined that the value of the PWM duty ratio is 100%, the power-down control flag is cleared (Step 121) and the control procedure proceeds to Step 122. When it is determined in Step 120 that the value of the PWM duty ratio is not 100%, the control procedure proceeds to Step 122. When the power-down control flag is detected in Step 118, 1% is added to the value of PWM duty ratio that is set in a previous stage (Step 128) and the control procedure proceeds to Step 122.
Next, the operation unit 40 determines whether or not the detected motor current value I is equal to or greater than the stop discrimination current threshold ISTOP (Step 122). When it is determined that the motor current value I is equal to or greater than the stop discrimination current threshold ISTOP (Step 122), the operation unit 40 stops the motor in Step 123 and the control procedure returns to Step 111. When it is determined that the motor current value I is less than the stop discrimination current threshold ISTOP (Step 122), the control procedure returns to Step 122. By repeating the above-described processing, striking is carried out in such a way that rotation by a high duty ratio is performed until just before a first striking is performed and the duty ratio is switched to the low duty ratio within less than one rotation from the start of the striking. Further, in a case where the motor current value I is equal to or less than the operation discrimination current threshold I1 even when the duty ratio is switched to the low duty ratio, the duty ratio is gradually increased at predetermined time intervals (each time interval in which the processing of the present flowchart is performed). Therefore, it is sufficient to perform either one of a process of setting the duty ratio to 40% or a process of adding a predetermined value to a duty ratio, depending on the motor current value I every time when the processing of the flowchart is performed. As a result, it is not necessary to secure a memory area for storing the peak current of the motor current value I. Further, there is no possibility that abrupt increase or decrease of the duty ratio is repeated. Accordingly, it is possible to prevent the striking from being unstable.
Next, a third embodiment of the present invention will be described with reference to
Next, in a case where the motor current 131 is increased again with progressing of the fastening and exceeds the current threshold I1 again at time t3 as in an arrow 131e, again, the operation unit 40 decreases the duty ratio of the PWM from 100% to 40%. Thereafter, the motor current 131 is maximized as in an arrow 131f by the retreat of the hammer 24 and then the engagement state between the hammer 24 and the anvil is released, so that the motor current 131 is decreased and a first striking is performed at time t4 in the vicinity where the motor current is lowermost (arrow 131g). At this time, the fastening torque value is increased as in an arrow 133b. The same striking is performed at times t5, t6 and the motor current at that time is increased or decreased as in arrows 131h to 131k. Then, since the motor current exceeds the stop discrimination current threshold ISTOP at time t7 as in an arrow 1311, the operation unit 40 stops the rotation of the motor 3. Meanwhile, the return current threshold (third threshold) IR of the duty ratio may be set to be sufficiently smaller than the current threshold I1 so that the motor current 131 after start of striking is not easily lowered less than the return current threshold (third threshold) IR when being decreased (arrows 131g, 131i, 131k).
Next, the operation unit determines whether or not the detected motor current value I is equal to or greater than the operation discrimination current threshold I1 (Step 147). When it is determined that the motor current value I is equal to or greater than the operation discrimination current threshold I1, the maximum value of the PWM duty ratio is set to 40% (Step 158) and the control procedure proceeds to Step 153. The operation unit determines whether or not the detected motor current value I is equal to or less than the return current threshold IR (Step 148). When it is determined that the motor current value I is equal to or greater than the return current threshold IR, the control procedure proceeds to Step 154. When it is determined that the motor current value I is equal to or less than the return current threshold IR, the detected motor current value I is stored in a current value memory included in the operation unit (Step 149). As the current value memory, a temporary storage memory such as RAM included in the operation unit can be used. Information for counting the elapsed time of the time detected may be stored together in the current value memory. Next, the operation unit causes a motor current peak detection timer to measure the elapsed time from the time when the motor current value I is equal to or less than the return current threshold IR. Then, the operation unit determines whether or not the measured time exceeds a certain period of time (Step 150). Here, when it is determined that the measured time does not exceed the certain period of time, the control procedure proceeds to Step 154. When it is determined that the measured time exceeds the certain period of time, the operation unit reads out a plurality of motor current values stored in the current value memory (Step 151). Next, the operation unit 40 determines whether or not the read-out motor current value I is continuously equal to or less than the return current threshold IR. When it is determined that the read-out motor current value I is continuously equal to or less than the return current threshold IR, the setting value of the PWM duty value is set to 100% (Step 153). When it is determined that the read-out motor current value I is not continuously equal to or less than the return current threshold IR, the control procedure proceeds to Step 158. Next, the operation unit 40 determines whether or not the detected motor current value I is equal to or greater than the stop discrimination current threshold ISTOP. When it is determined that the detected motor current value I is equal to or greater than the stop discrimination current threshold ISTOP, the operation unit stops the motor at Step 155 and the control procedure returns to Step 141. When it is determined that the detected motor current value I is less than the stop discrimination current threshold ISTOP (Step 154), the control procedure returns to Step 143.
In this way, in the present embodiment, the duty ratio is not immediately returned to 100 even when the motor current value I is temporarily equal to or less than the return current threshold IR due to some factors. In other words, the peak current I is observed and the duty ratio is returned to 100% after it is confirmed at Step 152 that the observed current value I is continuously equal to or less than the return current threshold IR. As a result, it is possible to effectively prevent a variation of the duty ratio due to noise or disturbance, etc. The switching of the duty ratio at time t2 as described in
By repeating the above-described processing, striking is carried out in such a way that rotation by a high duty ratio is performed until just before a first striking is performed and the duty ratio is switched to the low duty ratio just before less than one rotation from the start of the striking. Accordingly, it is possible to prevent breakage of the screw and also it is possible to securely perform the fastening at a fastening setting torque by plural times of striking. Further, since the motor 3 is driven so as not to generate torque higher than necessary at the time of striking, it is possible to significantly improve the durability of the electric tool even when using a high-power motor 3. Furthermore, since it is possible to reduce the power consumption of the motor 3 when performing the striking, it is possible to extend the life of the battery. Although it is observed that the state is continuous only when the motor current is equal to or less than the return current threshold IR in the third embodiment, the motor current may be continuously observed also when the detected motor current is equal to or greater than the operation discrimination current threshold I1.
As described above, in the third embodiment, in a case where it is assumed that the motor current 131 is increased by some accidental factors even when the duty ratio is decreased to 40% from 100%, the duty ratio is returned to 100% again and then the fastening work is continuously performed. Accordingly, it is possible to minimize the reduction of the fastening speed.
Hereinabove, although the present invention has been described with reference to the illustrative embodiments, the present invention is not limited to the above-described illustrative embodiments but can be variously modified without departing from the gist of the present invention. For example, although the impact tool to be driven by a battery has been illustratively described in the above-described illustrative embodiment, the present invention is not limited to the cordless impact tool but can be similarly applied to an impact tool using a commercial power supply. Further, although adjustment of the driving power during striking is performed by adjustment of the duty ratio of the PWM control in the above-described illustrative embodiment, the voltage and/or current applied to the motor during striking may be changed by any other methods.
This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2012-280363 filed on Dec. 22, 2012, the contents of which are incorporated herein by reference in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-280363 | Dec 2012 | JP | national |
This application is a continuation application claiming priority under 35 U.S.C. 120 to U.S. patent application Ser. No. 14/653,074 filed on Jun. 17, 2015, U.S. Pat. No. 10,562,160 issuing on Feb. 18, 2020, which was a U.S. national phase filing under 35 U.S.C. § 371 of PCT Application No. PCT/JP2013/084773, filed Dec. 18, 2013, and which in turn claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. JP2012-280363, filed Dec. 22, 2012, the entireties of which are incorporated by reference herein.
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