JP4551386B2 - Electric screwdriver - Google Patents

Description

  The present invention relates to an electric driver, and more particularly to an electric driver having a forward / reverse switching function.

Generally, an electric driver is configured to rotate the screw by transmitting the rotational driving force of the motor to the driver bit via a gear or clutch, and the load torque that the driver bit receives as a reaction from the screw side when the screw is tightened is set. When the value is reached, a predetermined cam works to disengage the clutch, and at the same time, the motor is stopped. In this case, there is a method of turning off the motor, but a method of applying a brake by power generation braking by operating a motor control circuit or a drive circuit to operate the motor as a generator is often used. Such a brake function upon completion of tightening has the advantage that the screw tightening cycle can be shortened as much as possible and the accuracy of tightening torque can be improved. Most electric drivers also have a reverse rotation function that reversely rotates the motor in order to loosen and remove the screw that was tightened by mistake. The user can use the mechanical forward / reverse selector switch to set the normal rotation mode and screw for screw tightening. Any one of the reverse rotation modes for loosening can be selected. As the motor, a brushed DC motor or an inverter-controlled brushless DC motor is often used.
JP 2006-62063 A

  In the conventional electric screwdriver, if the user makes a mistake in tightening the screw, the forward rotation mode of the screw tightening is terminated, the forward / reverse selector switch is switched from “forward” to “reverse”, and the driver bit is set again. The correct operating procedure of the forward / reverse switching function is to turn on the start switch after hitting the head (cross hole) of the screw.

  However, in actual use, the forward / reverse selector switch is often switched to “reverse” at the moment when the user notices a tightening error or failure during screw tightening. In that case, the control unit in the electric driver responds to such a fast forward / reverse switching operation (operation error) as it is, and immediately reverses the polarity or phase of the motor drive voltage. However, since the motor is still rotating forward at this time, the counter electromotive force is added to the driving voltage for reverse rotation. As a result, a very large current flows instantaneously in the motor winding and the motor drive circuit, which may cause destruction of the switching element (transistor). Although a large-capacity switching element is also used for this measure, not only the device cost is increased, but also the drive circuit board is enlarged and the entire driver is enlarged, and the usability is deteriorated. In particular, in a brushless motor, this problem appears remarkably because the inverter includes a large number of power transistors for switching.

  The present invention has been made in view of the problems of the prior art, and is easy to use so that no troubles or problems occur even if the user arbitrarily performs forward / reverse switching operation during the screw tightening operation. An object is to provide an electric screwdriver that greatly improves the efficiency of screw tightening work.

In order to achieve the above object, the electric screwdriver of the present invention is an electric screwdriver that can selectively switch between a forward rotation mode for screw tightening and a reverse rotation mode for screw loosening, and holds the driver bit detachably. A motor capable of forward and reverse rotation for driving the bit holder to rotate, a motor control unit for controlling the operation of the motor, and a first position and reverse rotation mode for selecting the forward rotation mode by a user's manual operation According to the state of the forward / reverse selector switch that can be switched between the second position for selecting the motor, the start switch for instructing the start of rotation of the motor, the forward / reverse selector switch, and the start switch. comprising an operating command unit which gives an instruction relating to rotation of the motor to the motor controller, the operation command section, the forward-reverse changeover switch said first position A circuit that electrically detects a state between the second position and generates a second brake signal, and is configured to output the brake command in response to the second brake signal; is, the when the forward and reverse change-over switch is switched to the second position from the first position, the brake command the operation command unit in response to the switch switching operation during the execution of the forward rotation mode Is applied to the motor control unit, and the motor control unit brakes the motor in accordance with the brake command.

In the above configuration, when the user switches the forward / reverse selector switch from the first position to the second position while the motor is rotating forward in the forward rotation mode for screw tightening, the operation command A second brake signal is generated in the unit, a brake command is output in response to the second brake signal, and a motor control unit operates in accordance with the brake command to brake the motor, preferably by dynamic braking. The energization control for the reverse rotation is not performed for the motor rotating in the forward direction. Thereby, an excessive current does not flow through the motor winding and the motor drive circuit. Also, the user can quickly perform the loosening (removal) operation of the screw at a reliable start timing by pressing the driver bit against the screw head again and immediately turning on the start switch.

  According to a preferred aspect of the present invention, when the forward / reverse selector switch is switched from the second position to the first position during execution of the reverse rotation mode, the operation command unit is responsive to the switch switching operation. A brake command is given to the motor control unit, and the motor control unit brakes the motor according to the brake command. Thus, even when the user switches the forward / reverse selector switch during reverse rotation of the motor in the reverse rotation mode for loosening the screw, the brake is applied, so that the motor drive circuit can be protected.

  According to a preferred aspect, the torque monitoring unit that generates the first brake signal when the load torque reaches the set value when the screw is tightened is provided, and the operation command unit receives the first command from the torque monitoring unit. A brake command is given to the motor control unit in response to the brake signal, and the motor control unit brakes the motor according to the brake command. As described above, even when the screw tightening is completed normally, the motor may be braked to shorten the time required for the screw tightening as much as possible and to improve the accuracy of the tightening torque.

  According to a preferred aspect, the start switch is responsive to the axial displacement of the bit holder, and generates a start signal when the axial pressing force is applied to the bit holder with a magnitude greater than a predetermined value. The start signal is released when the axial pressing force applied to the bit holder is released. The operation command unit gives a start command to the motor control unit in response to the start signal, and cancels the start command when the start signal is canceled. Then, the motor control unit starts energization for the rotational operation for the motor according to the start command, and stops energization for the motor when the start command is released.

  As another preferred mode of the start switch, in response to the displacement of the manual operation lever, a start signal is generated when the operation lever is pressed to a predetermined position, and the pressing force applied to the operation lever is released. The start signal may be canceled when the operation is performed.

  According to a preferred aspect, the operation command unit gives a start command to the motor control unit in response to the start signal, and releases the start command when the start signal is released. Then, the motor control unit starts energization for the rotational operation for the motor according to the start command, and stops energization for the motor when the start command is released.

  In another preferred embodiment, the operation command unit is set in response to the brake signal to generate a brake command while the start signal is active, and becomes inactive when the start signal is released. A self-holding circuit that is reset at the time of release and releases the brake command.

  According to the electric driver of the present invention, the above-described configuration and operation prevent any trouble or trouble from occurring even if the user arbitrarily performs forward / reverse switching operation during the screw tightening operation. Work efficiency can also be improved.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows an overall configuration of an electric driver according to a preferred embodiment of the present invention. This electric driver has a cylindrical housing 10 having a size suitable for being gripped with one hand. In the housing 10, a torque adjustment ring 14, a clutch portion 16, a gear portion 18, a motor 20, and a mounting substrate 22 are attached or accommodated in a row in order from the bit holder 12 toward the inner side or the rear side.

  The mounting board 22 has all or most of the electric components constituting the power supply circuit, the control circuit, the motor driving circuit, etc. mounted on the printed board in this electric driver. The motor 20 is composed of, for example, a three-phase brushless DC motor, and rotates by inverter control. The bit holder 14 is configured so that a driver bit 24 corresponding to a screw or screw to be tightened is detachably inserted and fixed. Further, the torque can be adjusted steplessly by turning the torque adjustment ring 14.

The clutch unit 16, a start signal for starting (start of rotation) SS driver bit 24 when pushed against the head of the screw _- a start switch 26 for generating a first for sudden stop when the tightening of the screw is completed A brake switch 28 for generating a 1 brake signal BR1 ₋ is provided.

The start switch 26 responds to, for example, axial displacement of the bit holder 12 or a member interlocked therewith, and the axial pressing force (reaction) is applied to the bit holder 12 via the driver bit 24 with a magnitude greater than a predetermined value. when it added, and turns on the position sensor such as a microswitch or Hall element, a start signal SS having the stepped waveform (e.g. H level → L level waveform) _- generates. When the pressing force in the axial direction which has been added to the bit holder 12 is released (release the driver bit 24 from the screw), turns off the position sensor, the start signal SS _- in the off (H level Return). The start signal SS ₋ generated from the start switch 26 is sent to an operation command circuit 36 (FIGS. 2 and 3) described later mounted on the mounting board 22.

The electric driver monitors the mechanical torque of a cam (not shown) or the like provided in the clutch unit 16 to determine whether or not the load torque received as a reaction from the screw side during screw tightening has reached a set value. When it is detected that the load torque has reached the set value, the torque monitoring unit turns on the brake switch 28, which is a position sensor such as a micro switch or a hall element, to generate a pulse waveform. The first brake signal BR1 ₋ is generated. The first brake signal BR 1 ₋ generated from the brake switch 28 is also sent to the operation command circuit 36 on the mounting board 22.

  For example, a slide type forward / reverse selector switch 30 is attached to the outer peripheral surface of the housing 10. This forward / reverse selector switch 30 can be slidably moved between the “forward rotation” position and the “reverse rotation” position by the user's manual operation, that is, can be switched. Generates a forward / reverse switching signal FR having a first logical value (for example, L level) indicating that the forward rotation mode for screw tightening has been selected, and when switched to the “reverse rotation” position, the user performs reverse rotation for screw loosening. A forward / reverse switching signal FR having a second logical value (for example, H level) indicating that the mode has been selected is generated. This forward / reverse switching signal FR is also given to the operation command circuit 36 on the mounting board 22.

  A connector of an electric cord 32 is attached to the rear end portion of the housing 10, and AC power having a commercial frequency is supplied through the electric cord 32.

  FIG. 2 shows a configuration of main electric circuits on the mounting substrate 22. As illustrated, a power supply circuit 34, an operation command circuit 36, a motor control circuit 38, and an inverter circuit 40 are mounted on the mounting substrate 22.

The power supply circuit 34 inputs a commercial AC voltage of, for example, 100 V from the commercial AC power supply 42 via the electric cord 32, and converts the input AC to a DC of a predetermined voltage level through a transformer and a rectifier circuit (not shown). The motor driving DC current is supplied to the inverter circuit 40, and the control internal power supply voltages V _DD and V _CC are supplied to the operation command circuit 36 and the motor control circuit 38.

The operation command circuit 36 receives the start signal SS ₋ , the first brake signal BR 1 ₋ and the forward / reverse switching signal FR generated from the start switch 26, the brake switch 28 and the forward / reverse switching switch 30, as described above. A command related to the operation of the motor 20 is determined by a predetermined logic or determination criterion in accordance with the state of the switches 26, 28, and 30, and the determined command is given to the motor control circuit 38 in the form of a signal. The configuration and operation of the operation command circuit 36 will be described in detail later.

  The motor control circuit 38 responds to each command from the operation command circuit 36 and controls the inverter circuit 40 to cause the brushless DC motor 20 to perform the operation (rotation, brake, stationary, etc.) as commanded. PWM control can be used for this inverter control. In order to obtain inverter switching timing, a rotation sensor 44 for detecting the rotation position of the rotor is attached to the brushless DC motor 20, and a three-phase rotor position signal RT generated from the rotation sensor 44 is controlled by the motor. It is provided to the circuit 38.

  The inverter circuit 40 is formed by connecting switching elements TR1 to TR6 including six power transistors to a three-phase winding (U, V, W) of the brushless DC motor 20 in a three-phase bridge. In response to the switching control signal, the switching elements TR1 to TR6 are selectively turned on and off sequentially in a predetermined phase sequence and cycle so that a three-phase motor drive current MI flows to the motor 20.

FIG. 3 shows a specific circuit configuration example of the operation command circuit 36 in this embodiment. The operation command circuit 36 receives a start signal SS ₋ from the start switch 26, a first brake signal BR ₋ from the brake switch 28, and a forward / reverse switching signal FR from the forward / reverse switching switch 30. In addition to a circuit that outputs a forward / reverse rotation command, a second brake signal BR2 ₋ that conditionally requests a motor brake operation similar to the first brake signal BR1 ₋ based on the state of the forward / reverse selector switch 30 is generated. Circuit.

A start signal SS ₋ from the start switch 26 (FIG. 1) is input to the receiving circuit 52 from the input terminal 50. The start signal receiving circuit 52 includes a resistor 54 connected between the signal input terminal 50 and the node Na, a resistor 56 connected between the power supply voltage terminal V _DD and the node Na, a node Na, and a ground potential. And a capacitor 58 connected between the two.

When screwing operation is not performed (when not pressed against the driver bit 24 screw head in this embodiment), the start switch 26 is in the off state, the start signal SS _- is still H level, the node The potential of Na is kept at the H level. When the user turns on the start switch 26 for the screwing operation, the start signal SS _- changes from H-level at step waveform to the L level, it changes the potential of the node Na from H level until then L level. A change in potential from the H level to the L level or a binary signal obtained at the node Na is given to the motor control circuit 38 from the output terminal 60 as a “start command”. Further, the binary signal of the node Na is given to both RS flip-flops 62 and 64 as a reset input (R).

The first brake signal BR 1 ₋ from the brake switch 28 is input to the reception circuit 68 from the input terminal 66. The first brake signal receiving circuit 68 has an input resistor 67, a coupling capacitor 70, and a timer circuit 72.

The first brake signal BR1 ₋ is kept at the H level in a steady state, and has an L level pulse waveform only when the load torque reaches a set value by tightening the screw. H level falls from the potential also H level of node Nb when the changes from H level to L level to L level, the timer circuit 72 has a constant pulse width in response to the falling edge _- first brake signal BR Output signal. The H level output signal from the timer circuit 72 is input to the RS flip-flop 62 as a set signal (S). Here, when the reset input (R) of the RS flip-flop 62 is at L level, that is, when the start signal SS ₋ is active (L level), the H level output from the timer circuit 72 is output. In response to the signal, the output (Q ₋ ) of the RS flip-flop 62 changes from the previous H level to the L level. Then, an output signal showing the same logical value change (H level → L level) as the output (Q ₋ ) of the RS flip-flop 62 is obtained at the output terminal 78 via the NAND gate 74 and the NOT circuit 76. The output signal is given to the motor control circuit 38 as a “brake command”. First brake signal BR _- even after the return from the active L level to the inactive H level, the self-holding function of the RS flip-flop 62 to the reset input (R) becomes the H level (the start switch 26 is turned off Until “brake command” is output continuously.

  The RS flip-flop 62 includes a pair of NOR gates 80 and 82. The timer circuit 72 may be replaced with a NOT circuit.

Incidentally, the brake switch 28 is provided in the clutch unit 16, for example, when it stops in a state of riding on the cam, a brake switch 28 is turned on _- the (first brake signal BR1 state of active L level) is held in There is. However, the output signal of the timer circuit 72 returns from the H level to the L level after a lapse of a fixed time from when the first brake signal BR1 ₋ falls from the H level to the L level. Thereby, when the start switch 26 is turned off, the reset input (R) of the RS flip-flop 62 becomes H level, and the RS flip-flop 62 is reset. That is, even if the brake switch 28 comes on the cam provided in the clutch portion 16 when the electric driver is stopped, the electric driver can be turned on by turning the start switch 26 off and then on again. Can be restarted normally.

  Even when a NOT circuit is used instead of the timer circuit 72, when the brake switch 28 is in the state of riding on the cam, the H level state of the NOT circuit, that is, the function of the coupling capacitor 70 (time constant function), that is, Since the H level state of the set input (S) of the RS flip-flop 62 lasts only for a predetermined time, if the reset input (R) of the RS flip-flop 60 becomes H level, the RS flip-flop 62 is reset at that time. The Then, when the start switch 26 is turned on again and the reset input (R) of the RS flip-flop 62 is set to the L level, the electric driver restarts normally.

  The forward / reverse selector switch 30 electrically corresponds to a movable contact 30M corresponding to a movable operation member (for example, a slide member), a first fixed contact 30F corresponding to a “forward rotation” position, and a “reverse rotation” position. The movable contact 30M is connected to the first fixed contact 30F when the user selects "forward rotation" by manual operation, and when the "reverse rotation" is selected, the movable contact 30M. Is configured to be connected to the second fixed contact 30R.

The movable contact 30M is connected to the ground potential. The first fixed contact 30F is connected to the node Nc via the resistor 84, and the second fixed contact 30R is connected to the node Nd via the resistor 86. Here, the node Nc is set at a connection point of a resistor 88 and a capacitor 90 connected in series between the power supply voltage terminal V _DD and the ground potential, and is connected to one input terminal of the NAND gate 92. . The node Nd is set at a connection point of a resistor 94 and a capacitor 96 connected in series between the power supply voltage terminal V _DD and the ground potential, and is connected to the other input terminal of the NAND gate 92. It is also connected to an output terminal 98 for forward rotation command / reverse rotation command.

  When the forward / reverse selector switch 30 is switched to the “forward rotation” position, that is, when the movable contact 30M is connected to the first fixed contact 30F, the potential of the node Nc is L level. The signal is given to the motor control circuit 38 from the output terminal 98 as a “forward rotation command”. At this time, the potential of the node Nd is at the H level, and the output of the NAND gate 92 is at the H level.

  Further, when the forward / reverse selector switch 30 is switched to the “reverse rotation” position, that is, when the movable contact 30M is connected to the second fixed contact 30R, the potential of the node Nc is at the H level. Is provided to the motor control circuit 38 from the output terminal 98 as a “reverse rotation command”. At this time, the potential of the node Nd is at L level, and the output of the NAND gate 92 is at H level.

Until the forward / reverse selector switch 30 switches from the “forward rotation” position to the “reverse rotation” position, that is, when the movable contact 30M is not connected to either the first fixed contact 30F or the second fixed contact 30R, Both the nodes Nc and Nd become H level, and the output of the NAND gate 92 changes from the previous H level to the L level. In this embodiment, resistors 84,86,88,94 constitute a second brake signal generating circuit 95 by the capacitor 90, 96 and NAND gate 92, a second brake signal output of the NAND gate 92 BR2 _- to. The second brake signal BR2 ₋ becomes active at the L level.

Second brake signal from the NAND gate 92 of the active L level BR2 _- when is output, the output of the next stage of the NOT circuit 100 becomes H level, which is given as a set input (S) to the RS flip-flop 64 . Here, when the reset input (R) of the RS flip-flop 62 is at the L level, that is, when the start signal SS ₋ is active (L level), the H level output from the NOT circuit 100. In response to the signal, the output (Q ₋ ) of the RS flip-flop 64 changes from the previous H level to the L level. Then, an output signal indicating the same logical value change (H level → L level) as the output (Q ₋ ) of the RS flip-flop 64 is obtained at the output terminal 78 via the NAND gate 74 and the NOT circuit 76. The output signal is given to the motor control circuit 38 as a brake command. Again, the second brake signal BR _- even after the return from the active L level to the inactive H level, that is, in the forward and reverse change-over switch 30 the movable contact 30M is connected to one fixed contact 30F, 30R Thereafter, the “brake command” is continuously output until the reset input (R) becomes the H level (until the start switch 26 is turned off) by the self-holding function of the RS flip-flop 64. The RS flip-flop 64 includes a pair of NOR gates 102 and 104.

  FIG. 4 and FIG. 5 are flowcharts showing main operation procedures of the electric driver in this embodiment (particularly, processing procedures of the operation command circuit 36 and the motor control circuit 38). The operation of this electric driver will be described below based on this flowchart.

When the power switch is input, the electric driver can be used. First, it is determined whether the forward / reverse selector switch 30 is switched to the “forward” or “reverse” position (step S ₁ ). Normally, the user switches the forward / reverse selector switch 30 to the “forward rotation” position when performing the screw tightening operation. As described above, when the forward / reverse selector switch 30 is switched to “forward rotation”, the forward / reverse switching signal FR obtained from the forward / reverse selector switch 30 is at L level, and the operation command circuit 36 determines that “forward rotation command”. Is issued. However, since the “start command” is not issued from the operation command circuit 36, the motor control circuit 38 keeps the inverter circuit 40 in the OFF state. Therefore, the brushless DC motor 20 is also stationary.

Then, when the user pushes against the driver bit in the screw head of the target tightening (cross hole), the start switch 26 is turned on, the start signal SS _- changes from H level until it to the active L level, As described above, the “start command” is issued from the operation command circuit 36 (step S ₂ ). Then, the motor control circuit 38 starts switching control of the inverter circuit 40 so as to rotate the brushless DC motor 20 in the forward direction in accordance with the “start command” and the “forward rotation command” from the operation command circuit 36 (step). S _3).

Thus, when the brushless DC motor 20 rotates in the forward direction, the rotational driving force is transmitted to the driver bit 24 through the gear portion 18, the clutch portion 16, and the bit holder 12, and the rotational torque of the driver bit 24 The screw is tightened. When this screw tightening is completed normally, that is, when the load torque reaches the set value (step S ₅ ), the first brake signal BR 1 ₋ having a pulse waveform is automatically output from the brake switch 28 at that time, In response, the operation command circuit 36 issues a “brake command”. The motor control circuit 38 receives the “brake command” in addition to the “start command” and the “forward command”, and brakes the brushless DC motor 20 by power generation braking through the inverter circuit 40 according to the “brake command” ( step S _6). The power generation braking of the brushless DC motor 20 is performed, for example, by turning on all the upper transistors TR1, TR2, TR3 and turning off all the lower transistors TR4, TR5, TR6 in the inverter circuit 40.

Thus, the rotation of the motor 20 is suddenly stopped by the brake function. When the user releases the head of the screw by pulling the driver bit 24, where the start switch 26 is turned off, the start signal SS _- changes from L level to it H-level (step S _7). In response to this, the operation command circuit 36 releases the “start command” to the motor control circuit 38 and simultaneously resets the flip-flop 62 to release the “brake command”. When the “brake command” is released, the motor control circuit 38 ends the inverter control for the dynamic braking, and turns off all the transistors TR1 to TR6 in the inverter circuit 40 (step S ₈ ). Thus, one cycle of the screw tightening work by standard operation is completed.

  The most characteristic operation in this embodiment is when the user switches the forward / reverse selector switch 30 to “reverse” during screw tightening. For example, when the screw hit point is wrong or when the screw is tilted, the user often switches the forward / reverse selector switch to “reverse” in a reflective manner at the moment when the user notices that. Such a forward / reverse switching operation during screw tightening is an early operation mistake in the conventional electric screwdriver, but in this embodiment, as described below, this operation never becomes an operation error.

In this embodiment, when the user switches the forward / reverse selector switch 30 to “reverse” before the screw tightening is completed (step S ₄ ), the forward / reverse selector switch 30 is moved from the “forward” position as described above. During the transition to the “reverse rotation” position, an active second brake signal BR2 ₋ is generated in the operation command circuit 36, and a “brake command” corresponding to the second brake signal BR2 ₋ is output. Upon receiving this “brake command” from the operation command circuit 36 in addition to the “start command” and “forward rotation command”, the motor control circuit 38 generates power to the brushless DC motor 20 under the same inverter control as when the screw tightening is completed. The brake is applied by braking (step S ₆ ).

  In this way, when the forward / reverse selector switch 30 is switched from “forward” to “reverse” while the motor 20 is rotating forward for screw tightening, the motor 20 is energized for reverse rotation. Rather than conducting, energization for power generation braking is performed. Thus, an excessive current does not flow through the motor 20 and the inverter circuit 40, and the switching transistors TR1 to TR6 and the like do not fail.

  When the forward / reverse selector switch 30 is switched to the “reverse rotation” position, the forward / reverse switching signal FR becomes H level, and the operation command circuit 36 outputs a “reverse rotation command”. However, since the “brake command” is also output at the same time, the motor control circuit 38 ignores this “reverse rotation command”.

When the user releases the driver bit 24 from the screw was interrupted screw tightening, where the start switch 26 is turned off, the start signal SS _- changes from L level to it inactive H level (step S ₇ ). Also in this case, the operation command circuit 36 cancels the “start command” to the motor control circuit 38 and simultaneously resets the flip-flop 64 to cancel the “brake command”. When the “brake command” is released, the motor control circuit 38 ends the inverter control for the dynamic braking and turns off all the transistors TR1 to TR6 in the inverter circuit 40 (step S ₈ ).

Usually, immediately after this, the user presses the driver bit 24 against the head of the screw again to perform the screw loosening (removal) operation in the reverse rotation mode. In this case, the start switch 30 is turned on with the forward / reverse selector switch 30 in the “reverse rotation” position (steps S ₁ → S ₁₀ ), and the “reverse rotation command” and the “start command” are simultaneously sent from the operation command circuit 36. In response to these commands, the motor control circuit 38 starts switching control of the inverter circuit 40 so as to rotate the brushless DC motor 20 in the reverse direction (step S ₁₁ ).

When the screw is loosened by this reverse rotation operation, the user pulls the driver bit 24 away from the screw head, so the start switch 26 is turned off (step S ₁₃ ), and the operation command circuit 36 releases the “start command”. In response to the cancellation of the “start command”, the motor control circuit 38 turns off all the transistors TR1 to TR6 in the inverter circuit 40 (step S ₁₆ ), and stops the brushless DC motor 20 without using a brake.

As a very special usage, immediately after the user starts the reverse rotation operation of loosening the screw, the forward / reverse selector switch 30 is moved from the “reverse rotation” position to the “forward rotation” position while the driver bit 24 is pressed against the head of the screw. There is also a case of switching (step S ₁₂ ). Again, in this embodiment, the operation instruction circuit 36 and the second brake signal BR2 _- Activate the outputs "brake command", the motor control circuit 38 in accordance with the "brake command" is the same inverter control as the braking by dynamic braking to the brushless DC motor 20 (step S _14). Immediately after that, when the user releases the driver bit 24 from the screw, the start switch 26 is turned off (step S ₁₅ ), and the “start command” is released from the operation command circuit 36, and the motor control circuit 38 switches the inverter circuit 40. Completely off (step S ₁₆ ).

  As described above, in the electric driver of this embodiment, when the user switches the forward / reverse selector switch 30 from “forward rotation” to “reverse rotation” during screw tightening, the motor is operated in accordance with the switching operation. 20 is not energized for reverse rotation, but is braked by dynamic braking to stop the motor 20 suddenly, so that an excessive current does not flow through the windings of the motor 20 and the inverter circuit 40. As a result, it is not necessary to use a large-capacity large switching transistor for the inverter circuit 40 occupying a large area on the mounting substrate 22, so that the mounting substrate 22 can be made smaller and the housing 10 can be made compact.

  Further, when the user performs forward / reverse switching operation during such screw tightening, after the brake is applied, the driver bit 24 is once separated from the screw head and immediately pressed again. The electric screwdriver can start screw loosening (removal) by reverse rotation at a timing conscious of itself. This usability is very important in preventing damage to the screw head. That is, if screw loosening (removal) due to reverse rotation is unexpectedly started while the driver bit 24 is loosely fitted in the screw head (cross hole), the screw head may be damaged. In that respect, in the electric driver of this embodiment, the start switch 26 is turned on at a timing at which the user can control himself / herself, so that the screw is loosened (removed) with sufficient pressing force applied to the screw head. The reverse rotation operation can be started, and there is no possibility that the screw head is damaged. Accordingly, since the screw tightening operation can be performed with confidence without worrying about undesired screw head damage, the efficiency of the operation is improved as a result.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made within the scope of the technical idea.

  For example, a brushed DC motor can be used instead of a brushless DC motor, and a motor drive circuit other than an inverter circuit can be used. Further, in the above embodiment, the start switch 26 that is turned on / off in response to the axial displacement of the bit holder 12 is provided, and the start switch 26 is turned on when a pressing force exceeding a predetermined value is applied to the driver bit 24. Configured to do. However, although not shown, for example, a trigger-type or push-type lever may be attached to the housing 10 and the user may operate this lever to turn on / off the start switch. That is, the start switch may be turned on when the user pushes the lever with his finger, and the start switch may be turned off when the user releases the pressing force by releasing the finger from the lever.

  In the above embodiment, the electrical system such as the motor 20, the motor control circuit 38, the forward / reverse selector switch 30, the start switch 26, the operation command circuit 36, the inverter circuit 40, and the power supply circuit 38 is provided in the housing 10. However, a configuration in which a part (for example, the motor control circuit 38) or all of those electric systems other than the motor 20 is provided in a separate unit is also possible.

  Further, the forward / reverse selector switch 30 may have a configuration in which a “neutral” position is provided between the “forward rotation” position and the “reverse rotation” position. In this case, the operation command circuit 36 or the motor control circuit 38 can be configured so that the motor does not rotate even when the start switch is turned on when the position is switched to the “neutral” position. However, when the start switch is turned on and switched to “neutral” during motor rotation, the “brake” function according to the present invention may be activated.

1 is a schematic side view showing an overall configuration of an electric driver according to an embodiment of the present invention. It is a block diagram which shows the structure of the main electric circuits in the electric driver of embodiment. It is a circuit diagram which shows the specific circuit structural example of the operation command circuit in the electric driver of embodiment. It is a flowchart figure which shows the main operation | movement procedures (control procedure of a control system) in the electric driver of embodiment. It is a flowchart figure which shows the main operation | movement procedures (control procedure of a control system) in the electric driver of embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Housing 12 Bit holder 20 Motor 24 Driver bit 26 Start switch 28 Brake switch 30 Forward / reverse switch 34 Power supply circuit 36 Operation command circuit (operation command part)
38 Motor control circuit 40 Inverter circuit 52 Start signal reception circuit 62 RS flip-flop 64 RS flip-flop 68 First brake signal reception circuit 95 Second brake signal generation circuit

Claims (8)

An electric driver capable of selectively switching between a forward rotation mode for screw tightening and a reverse rotation mode for screw loosening,
A reversible motor for rotationally driving a bit holder that detachably holds a driver bit;
A motor control unit for controlling the operation of the motor;
A forward / reverse selector switch that can be switched between a first position for selecting the forward rotation mode and a second position for selecting the reverse rotation mode by a user's manual operation;
A start switch for instructing rotation start of the motor;
The instructions relating to the rotation operation of the motor; and a operation command unit giving the motor controller in accordance with the state of the forward-reverse changeover switch and the start switch,
The operation command section includes a circuit that electrically detects a state in which the forward / reverse selector switch is between the first position and the second position and generates a second brake signal; Configured to output the brake command in response to a second brake signal;
When the forward / reverse selector switch is switched from the first position to the second position during execution of the forward rotation mode, the operation command section responds to the switch switching operation and sends the brake command. Giving to the motor control unit, the motor control unit brakes the motor according to the brake command ,
Electric screwdriver. When the forward / reverse selector switch is switched from the second position to the first position during execution of the reverse rotation mode, the operation command unit responds to the switch switching operation and sends the brake command to the motor. supplied to the control unit, the motor control unit brakes the motor in accordance with the brake command, electric screwdriver according to claim 1. A torque monitoring unit that generates a first brake signal when the load torque reaches a set value during screw tightening;
The operation command unit in response to said first brake signal from the torque monitoring unit gives the braking command to the motor controller, the motor control unit brakes the motor in accordance with the brake command, wherein The electric driver according to claim 1 or claim 2. The electric driver according to claim 1 , wherein the motor control unit brakes the motor by power generation braking. The motor is a brushless DC motor, electric screwdriver of claim 4. The start switch responds to an axial displacement of the bit holder, and generates a start signal when an axial pressing force is applied to the bit holder with a magnitude greater than a predetermined value, and is applied to the bit holder. Release the start signal when the axial pressing force was released,
The operation command unit gives a start command to the motor control unit in response to the start signal, and cancels the start command when the start signal is released,
6. The motor control unit according to claim 1, wherein the motor control unit starts energization for a rotational operation on the motor according to the start command , and stops energization of the motor when the start command is released. The described electric screwdriver. The start switch responds to the displacement of the manual operation lever, generates a start signal when the operation lever is pressed to a predetermined position, and releases the pressing force applied to the operation lever. Cancel the start signal,
The operation command unit gives a start command to the motor control unit in response to the start signal, and cancels the start command when the start signal is released,
6. The motor control unit according to claim 1, wherein the motor control unit starts energization for a rotational operation on the motor according to the start command , and stops energization of the motor when the start command is released. The described electric screwdriver. The operation command unit is set in response to the brake signal while the start signal is active, generates the brake command, and is reset when the start signal is released and becomes inactive. It said having a self-holding circuit for releasing the brake command, electric screwdriver according to any one of claims 1-7 Te.

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