JP7506912B2 - Electric cutting tools - Google Patents

Description

The present invention relates to electric cutting tools for horticulture, such as hedge trimmers, reciprocating saws, and clippers, used to cut trees and plantings, and in particular to electric cutting tools that use a DC motor as the drive source.

With the widespread use of neodymium magnets and lithium-ion batteries, gardening cutting tools that previously used gasoline engines, such as hedge trimmers and reciprocating saws, can now be electrified, contributing to solving environmental problems by reducing noise and the use of fossil fuels.

The electric motors used in these devices are preferably DC motors such as brushless DC motors or DC motors with brushes, in view of their efficiency and torque characteristics.
FIG. 7 shows a brushed DC motor as a representative example of a DC motor 101. A stator 102 doubles as an outer circumferential case, and is provided with a two-pole permanent magnet field 102a on its inner circumferential surface. The rotor 103 is an inner rotor type motor in which a rotor 103 is rotatably provided inside the outer circumferential case surrounded by the stator 102. The rotor 103 is provided with a rotor core 103b rotatably provided around a rotor shaft 103a. Three pole teeth 103c are provided on the rotor core 103b so as to protrude radially outward, and a three-phase coil 103d is wound around the pole teeth 103c. The three-phase coil 103d is delta-connected and connected to a commutator 104 provided on the rotor shaft 103a. A brush 105 is slidably in contact with the commutator 104. The three-phase coil 103d may be star-connected, with one end of the three-phase coil 103d being commonly connected as a common. A direct current supplied from power supply terminals 105a and 105b is rectified by brushes 105 and a commutator 104, and is passed through a three-phase coil 103d at 120 degrees to generate a rotating magnetic field, causing the rotor 103 to rotate continuously.

FIG. 8 shows an example of a block diagram of a brushed DC motor drive circuit.
The power source is a rechargeable battery 51 (BATTERY). The power current is supplied to the power terminals (IN-A, B) of the drive circuit 53 (DRIVER) through a power switch 52 (PWR-SW). The drive circuit 53 (DRIVER) is composed of a microcontroller control circuit 54 (MPU) and an H-bridge output circuit 55 (INV), and the coil outputs (OUT-A, B) are connected to the power terminals (P, N) of a brushed DC motor 56 (MOTOR). A rotation sensor 57 (SENSOR) is also disposed near the motor and sends a rotation signal (FG) to the control circuit 54 (MPU).
The coil current sensor 58 (resistor: RS) detects the coil current and sends a current signal (CUR) to the control circuit 54 (MPU).

A control circuit 54 (MPU) inputs a signal (RUN) from a rotation command switch (RUN-SW), a signal (DIR) from a rotation direction command switch (DIR-SW), a signal (FG) from a rotation sensor 57 (SENSOR), and a signal (CUR) from a coil current sensor 58 (RS), and outputs gate signals (GATE-1 to 4) to an output circuit 55 (INV).
By outputting the gate signal appropriately, the coil output is energized, and the energization modes of forward rotation, reverse rotation, brake, and stop can be selected, and torque can be controlled by PWM control. Regarding the energization modes, for example, when GATE-1 and GATE-4 are turned on, the motor P terminal is connected to +V and the N terminal is connected to GND, and the motor rotates forward. When GATE-2 and GATE-3 are turned on, the motor P terminal is connected to GND and the N terminal is connected to +V, and the motor rotates reversely. When GATE-2 and GATE-4 are turned on, both the motor P terminal and N terminal are connected to GND, and a short-circuit brake is applied. When GATE-1 to 4 are turned off, both the motor P terminal and N terminal are released (high impedance state), and the motor stops. If a three-phase brushless DC motor is used instead of a three-phase brushed DC motor, the H-bridge circuit of the drive circuit (DRIVER53) can be replaced with a three-phase inverter circuit, and the motor can be driven by inputting a position sensor signal such as a Hall IC.

Below, examples of prior art relating to electric gardening cutting tools using DC motors are given.
The first document is a proposal for improving the operability of a hedge trimmer, and shows an example of the configuration of an electric hedge trimmer. There are two types of hedge trimmers: one for trimming the tips of hedges or tree branches by stacking two linear blades with many triangular blades and reciprocating them in opposite directions, and one for trimming lawns (called clippers) by stacking two blades with multiple triangular blades and oscillating them in opposite directions (see Patent Document 1).

The second document is a proposal for suppressing vibrations in reciprocating saws, and shows an example of the configuration of an electric reciprocating saw. A reciprocating saw cuts tree branches by reciprocating a single linear blade with multiple triangular blades arranged in a row, and for high branches, the motor and blade are placed at the tip of a long pole (see Patent Document 2).

Electric gardening cutting tools used to cut trees and plants, such as hedge trimmers, reciprocating saws, and clippers, require a mechanism (cam or crank) to convert the rotational motion of the motor into reciprocating motion. Because the motor always rotates in the same direction, it is prone to uneven wear, which can cause vibration, noise, and reduced efficiency.
It is also known that when using a brushed motor, running it in a fixed direction causes dirt to accumulate on the brushes, making it prone to breakdowns.
In addition, during cutting work, the blade may bite into the material being cut and stop the tool, or in the case of a two-blade structure like a hedge trimmer, foreign objects such as clothing or dirt may get caught in the gap between the sliding surface and the cutting surface, causing a sudden stop (hereinafter referred to as a jamming stop). In order to resume work, the material to be cut must be removed from the blade, which is time-consuming and may cause injury. Furthermore, there are cases where the tool cannot be removed without disassembling and repairing it, which significantly reduces work efficiency and the maintenance costs of the tool.

Figure 9 shows an example of the cutting blade shape of the electric cutting tool. The horizontal cross section (X-X' cross section) of the cutting blade 61 is roughly trapezoidal, with both oblique sides being blade portions 62 with blades. When the cutting blade 61 reciprocates over a distance longer than the pitch in the figure, the blade portions 62 on both sides come into contact with the workpiece alternately, and the cutting ability is equal in the forward and backward directions and is not dependent on the direction of movement of the cutting blade 61. Therefore, the motor 56, which is the driving source, may be driven to rotate in either forward or reverse direction.

Taking advantage of this feature, a method has been proposed in which the rotation direction of the motor is reversed to change the operating direction of the cutting blade as a means of separating the cutting blade from the workpiece when the cutting blade stops due to engagement. Patent Document 3 is one example, in which the speed change mechanism is switched in conjunction with a switching means that reverses the operating direction of the cutting blade of a hedge trimmer. In general, to switch the operating direction of the cutting blade, a rotation direction command switch is provided for the motor, and the rotation direction is switched before the rotation command switch is operated, and in addition to the rotation command switch, a rotation direction command switch switching operation is required to specify the rotation direction (see Patent Document 3).

JP 2019-134693 A JP 2019-198961 A JP 2005-269972 A

During cutting operations, the motor always rotates in the same direction, and it is desirable to reduce vibration and noise caused by uneven wear on the cam mechanism, etc., which results from the motor rotating in a fixed direction, and to reduce failure of the brushes in brush motors and improve reliability.
In addition, the recovery operation when the cutting blade stops due to biting, i.e., the recovery operation of separating the cutting blade from the workpiece, requires the cutting operation to be interrupted once, and even if the method described above of reversing the motor is adopted, it takes time and effort, resulting in a decrease in work efficiency.
Figure 10 shows an example of a timing chart for reversing the motor to release the jammed stop, and will explain the decrease in work efficiency in detail. PWR-SW is the power switch, RUN-SW is the rotation command switch, DIR-SW is the rotation direction command switch, and FG is the rotation signal. MOTOR is the motor, which rotates according to the RUN-SW input, and the rotation direction is switched according to the DIR-SW, with CW (forward rotation) and CCW (reverse rotation) written in the diagram. The series of processes that turn the motor on and off is called an on cycle, and the number of on cycles is written at the bottom, and the specific recovery procedure will be explained below for each on cycle.

The case where the cutting blade jammed during on cycle 1 and the cutting operation stopped is shown as an example.
When a jam occurs, the operator immediately turns off the RUN-SW and stops the power supply to the motor. Next, the DIR-SW (rotation direction command switch) is switched to the reverse direction, and then the RUN-SW (rotation command switch) is turned on again to start the reverse rotation (ON cycle 2). The operator visually checks whether the workpiece has been separated, and if it has not been completely separated, stops the motor again, removes it by hand, and restarts it (ON cycle 3). Once the workpiece has been separated, the RUN-SW (rotation command switch) is turned off again, and when the motor has stopped, the DIR-SW (rotation direction command switch) is returned to the forward direction, and the RUN-SW (rotation command switch) is turned on again to resume the cutting operation (ON cycle 4).
As such, the recovery procedure when the cutting blade stopped working was complicated and time-consuming, and there was also a risk of injury to the fingertips if the cutting blade came into contact with them.

In addition, electric cutting tools have a large inertia and will continue to rotate by inertia for several seconds even after the power supply is cut off, so if the direction of rotation is switched during inertia and the tool is started, a reverse brake proportional to the induced voltage will occur. In actual cutting work, there are many cases where the rotor does not stop after a short stop command and restarts during inertia, so when adopting a method of switching the direction of rotation, it is necessary to consider the possibility of starting in the opposite direction to the inertia rotation and causing a reverse brake. When a reverse brake occurs, stress is applied to the mechanism, inducing a mechanical failure, and an excessive brake current flows, which may deteriorate the motor coil, drive circuit, battery, etc., causing damage or burning. Tools that do not solve this problem will inevitably be products with extremely low reliability.
There are also various methods that can be considered for automatically detecting and releasing the jammed state using the drive circuit, but the load conditions vary widely, making perfect automation difficult and increasing costs. Moreover, since this is a hand-held tool that the operator may need to remove the jammed material using his or her hands or pruning shears, for the cutting blade to operate automatically without the operator's intention, this reduces the operator's sense of security regarding the tool and could even cause injury, making it unsafe from a safety standpoint.

The object of the present invention is to provide an electric cutting tool that solves the problems of the prior art described above, reduces uneven wear of the mechanism or failure of the brushes of the brush motor, improves the reliability of the device, and, if the cutting blade jams into the workpiece and stops, resolves the jammed state without interrupting the cutting operation, improving work efficiency and safety, while also reducing the cost of the tool and extending its lifespan.

An electric cutting tool in which a cutting section having cutting blades on both sides in a forward and backward directions is reciprocated by a DC motor, the cutting section being provided with: a drive circuit capable of rotating the DC motor that drives the cutting section in forward and reverse directions; and a rotation command input unit that sends a rotation command to the drive circuit, the drive circuit being provided with: a rotation state detection unit that detects the rotation state of the motor in response to an input from the rotation command input unit; a rotation direction storage unit having a non-volatile memory that retains information on the rotation direction of the motor even when power to the drive circuit is cut off; a control circuit having a gate output unit that outputs a gate signal in accordance with the rotation direction of the motor; and an output circuit that energizes the DC motor through an output element group in response to the gate signal output from the gate output unit, When a rotation command is input from a command input unit , the rotation state of the motor is detected by the rotation state detection unit, and the rotation state detection unit measures the coil voltage in a non-energized state to detect an induced voltage or detects a period of a rotation sensor signal. If the control circuit determines that the motor is rotating based on these detection results, it holds the rotation direction information stored in the rotation direction memory unit without changing it, and if it determines that the motor is stopped, it rewrites the rotation direction information stored in the rotation direction memory unit so as to invert it and executes a start-up routine, determines the rotation direction of the motor in accordance with the rotation direction information stored in the rotation direction memory unit, outputs a gate signal from the gate output unit, and energizes the DC motor via the output circuit to start it.

Electric cutting tools have a large inertia and will continue to rotate by inertia for several seconds even after the power supply is cut off. If the tool is restarted in the opposite direction while rotating by inertia, reverse braking will be applied, which may cause damage to the mechanism and circuitry. Therefore, the previous rotation direction is stored in a non-volatile memory, and when a rotation command is input, the rotation state of the motor is detected by the rotation state detection unit and the tool is started according to the required start routine. This makes it possible to avoid reverse braking by matching the direction of inertia rotation with the starting direction. In addition, no stress is generated in the mechanism, preventing mechanical failures, and since excessive braking current does not flow, there is no possibility of the motor coil, drive circuit, battery, etc. deteriorating and being damaged or burned, improving reliability.
Specifically, if the motor is rotating when a rotation command is input, it will start in the same direction as the previous time. It is self-evident that the inertial rotation and the previous rotation direction will match, so the inertial rotation direction and the starting direction will match, making it possible to avoid reverse braking. Also, if the motor is stopped when a rotation command is input, it can start in either direction, but it will start in the opposite direction to the previous time. This reduces uneven wear on the mechanism and brush failure in brushed motors by reversing the rotation every time the motor stops, and furthermore, when the motor stops due to jamming, the jammed state can be released without interrupting the cutting operation.

The control circuit may detect a rotation state of the motor when power is supplied to the drive circuit and execute a start-up routine.
This can be applied to cases where the drive circuit is energized by a power switch and the motor is started instead of by operating the rotation command input unit. In this case, if the drive circuit is configured to start the motor when the power supply to the drive circuit is turned on, there is no need to give a rotation command, and the rotation command input unit can be omitted and the motor can be operated using only the power switch.

A DC power source may be constantly applied to the drive circuit, and the control circuit may be in a sleep mode in which the microcontroller is in a standby state; when a rotation command is input from the rotation command input unit to the control circuit, the microcontroller switches from the sleep mode to a wake-up mode based on the input rotation command; and when the control circuit switches to the wake-up mode, it detects the rotation state of the motor and executes a start-up routine.
As a result, when a rotation command is input from the rotation command input unit to the control circuit, the microcontroller switches from sleep mode to wake-up mode based on the input rotation command, energizes the drive circuit in wake-up mode, and at this timing detects the rotation state of the motor and executes a start-up routine. In other words, the device can be used with the drive circuit energized, and can be operated with only the rotation command switch without a power switch. Also, when the motor stops, the drive circuit goes into sleep mode, consuming almost no power and thus saving energy.

With the electric cutting tool described above, if the cutting blade becomes stuck in the workpiece and stops, the stuck state can be resolved without interrupting the cutting operation, improving work efficiency and safety, while also achieving low cost and long life for the tool.
In addition, the work to resolve jamming, which previously required complicated switch operations and time, can now be done by simply operating the rotation command input unit (rotation command switch), dramatically improving operability, work efficiency, and safety. Costs can also be reduced by omitting the rotation direction command switch and rotation sensor. In addition, by reversing the rotation at each start and stop, uneven wear on the mechanism can be reduced, reducing vibration and noise, and in the case of brushed motors, dust from the brushes can be removed, reducing failures caused by the brushes.
In addition, when an instantaneous off operation is performed to momentarily turn off the power switch or rotation command switch and the motor is rotating by inertia, the motor will rotate smoothly in the same direction without reversing, preventing reverse braking and damage to the mechanism and circuitry.
In the case of a high-power tool, the drive circuit can be energized, start and stop can be controlled by a small-capacity rotation command switch, and current can be applied to the motor by a large-capacity output element.

FIG. 1 is a diagram showing the configuration of an electric gardening cutting tool. FIG. 2 is a timing chart showing the start when the engagement stops. FIG. 3 is a timing chart showing the start-up during coasting. FIG. 4 shows an example of a motor drive circuit for inputting a rotation command. FIG. 5 shows an example of a motor drive circuit that turns the power supply on and off. FIG. 6 is a flow chart showing a motor starting routine. FIG. 7 shows an example of a brushed DC motor. FIG. 8 shows an example of a motor drive circuit having a conventional configuration. FIG. 9 shows examples of the shapes of the cutting blade. FIG. 10 is a timing chart showing the stop of engagement in a conventional circuit. FIG. 11 is a cross-sectional view showing a main part of a hedge trimmer.

Embodiments of an electric cutting tool according to the present invention will be described below with reference to the accompanying drawings. The present invention will be described by taking as an example an electric cutting tool for gardening, such as a hedge trimmer, a reciprocating saw, or a clipper, for cutting trees, plantings, etc. The DC motor may be a delta-connected inner rotor type brushed DC motor as shown in FIG. 7, or a BLDC (brushless DC) motor with a permanent magnet field in the rotor, a star-connected stator with windings arranged with a 120° phase difference, and a phase end connected to a motor output circuit.

FIG. 1 shows an example of the configuration of an electric gardening cutting tool.
The housing-shaped exterior case 1 contains a battery 2, a motor drive circuit 3, a DC motor 4, a motor shaft 5 (output shaft), and a cutting unit 7 having a cutting blade 6. The motor shaft 5 extends from the exterior case 1 to the outside, and the cutting blade 6 is driven to reciprocate around the motor shaft 5 to cut the part to be cut (trees, plantings, etc.). The battery 2 is a battery that can be charged from a commercial power source, and is detachably attached to the exterior case 1.

Figure 11 illustrates a cross section of a main part of a hedge trimmer as an example of an electric cutting tool for gardening. The hedge trimmer has a pair of clipper blades (cutting blades 6) at the cutting section 7. A motor case 4a is fixed inside the outer case 1 with screws. A stator is integrally assembled to the inner circumferential surface of the motor case 4a. The stator includes a stator magnet 4b fixed to the inner circumferential surface of the motor case 4a and a brush 4c that supplies power to a coil 5b described later. The motor case 4a forms a back yoke for the stator magnet 4b. A pair of rolling bearings 4d are respectively assembled to the motor case 4a and the outer case 1, and the motor shaft 5 is rotatably supported. The rotor is integrally assembled to the motor shaft 5 with a rotor core 5a. A coil 5b is wound around the pole teeth protruding radially outward from the rotor core 5a. The coil lead drawn out from the coil 5b is connected to a commutator 5c (commutator) provided at the opposite output end of the motor shaft 5. A power supply brush 4c fixed to the motor case 4a is constantly in contact with the commutator 5c and slides as the motor shaft 5 rotates.

The cutting section 7 is provided at the output end of the motor shaft 5. The cutting section 7 is attached to an eccentric cam 20 that rotates around the motor shaft 5 and is prevented from falling off. The eccentric cam 20 has a pair of cam parts 20a that are 180 degrees out of phase with each other around the motor shaft 5. A clipper blade (cutting blade 6) is attached to each cam part 20a. When the motor shaft 5 rotates in either the forward or reverse direction, the eccentric cam 20 also rotates, and the pair of clipper blades (cutting blades 6) attached to the pair of cam parts 20a reciprocate in the opposite direction. This allows the part to be cut, such as a twig, to be sheared by the pair of clipper blades (cutting blades 6).

First, we will explain the cutting operation in which the rotation direction is reversed when the rotation stop of the DC motor 4 is detected. When the cutting section 7, which has symmetrical cutting blades 6 on both the forward and backward sides, moves back and forth, the cutting process is the same even if the direction of movement is reversed, so bidirectional operation is possible. Therefore, if the DC motor 4 is in a rotation stopped state when the power is turned on or a rotation command is input, the rotation direction is reversed and it is started. With conventional gasoline engine-type cutting tools, it is difficult to change the rotation direction, and operation in a fixed direction is the norm, but with the DC motor 4, forward and reverse operation is easy, making bidirectional operation possible.

By adding a function to start the DC motor 4 in reverse if it is stopped when a rotation command is input, the DC motor 4 will start in reverse even if the cutting blade 6 bites into the workpiece and stops, and as a result the cutting part 7 will also move in the opposite direction, separating the cutting blade 6 from the workpiece. What is important here is that the operator can release the jammed state simply by operating the rotation command switch, just as in normal work. This is a major difference from the conventional method of operating a reverse switch or the method of automatically detecting jamming and starting reverse rotation, improving operability and safety. Furthermore, if a large torque is required to start reverse rotation after a jammed stop, this can be achieved by, for example, instantaneously doubling the starting torque by increasing the current limit value for a specified period at start-up.

The condition for reversing the direction of rotation is that the DC motor 4 is stopped when a rotation command is input, and it is necessary to determine whether the motor has stopped. This can be achieved by installing a rotation sensor on the DC motor 4 to monitor the rotation speed, but installing a rotation sensor is disadvantageous in terms of space and cost. Hall sensors that detect rotor magnetic flux are often used as rotation sensors, but brushed motors in particular are structured so that the coil rotates but the magnet does not rotate, so simply installing a Hall sensor will not be able to detect inertial rotation; instead, a separate ring magnet must be installed on the motor shaft to detect rotation, which requires considerable cost and space. In fact, there are cases in which ring magnets and Hall sensors are added to brushed motors for on-board accessories.

Therefore, it is desirable to detect the stopped state of the motor without using a rotation sensor, and the stopped state can be determined by extracting rotation information from the coil output current or coil output voltage. Alternatively, the stopped state can be determined from the control amount of the control program, such as the excitation period. Furthermore, it is possible to detect the stopped state by using communication or power interruption as an information source in cooperation with an intelligent battery. With these methods, the stopped state can be detected by monitoring the motor output with the rotation state detection unit 13a provided in the control circuit 13 (MPU), and the rotation sensor and wiring provided on the motor can be omitted.

FIG. 5 is a block diagram of the motor drive circuit 3 equipped with a nonvolatile memory.
Power is supplied from a battery 2 (BATTERY), which is turned on and off by a power switch 11 (PWR-SW), and power is supplied to the IN-A and IN-B terminals of a drive circuit 12 (DRIVER). A DC motor 4 (MORTOR) is a brushed DC motor equipped with P and N terminals, and is energized by drive circuit outputs OUT-A and OUT-B. When the polarity is reversed, the motor rotates in the reverse direction. The drive circuit 12 (DRIVER) is composed of a control circuit 13 (MPU) and an output circuit 14 (INV: inverter circuit).

The control circuit 13 (MPU) is composed of a microcontroller, and receives rotation information FG and a signal (CUR) from the coil current sensor 15 (RS) to a rotation state detection unit 13a, and outputs gate signals GATE-1 to GATE-4 of the H-bridge circuit accordingly to control the start/stop and rotation direction of the DC motor 4. It also has a built-in non-volatile memory 16 (EEPROM) to store rotation direction information.
The output circuit 14 (INV) configures an H-bridge circuit with output elements Q1 to Q4 driven by gate signals GATE-1 to GATE-4 from the control circuit 13 (MPU), and outputs coil outputs OUT-A and OUT-B to the DC motor 4 (MOTOR).

Fig. 6 is a general flow chart showing a motor start routine in accordance with the control program of the motor drive circuit 3 in Fig. 5. When the power switch 11 is turned on, the following four steps are performed. The control circuit 13 (rotation state detection unit 13a) detects the rotation state of the motor and obtains motor rotation information (STEP 1). If the DC motor 4 is rotating, the process proceeds to STEP 4, and if the DC motor 4 is stopped, the process proceeds to STEP 3 (STEP 2). The rotation direction information is reversed (STEP 3). The DC motor 4 is rotated (STEP 4).
The motor rotation operation starts in reverse if the motor is in a stopped state when power is turned on. Also, if the power switch 11 is turned off momentarily when power is turned on, the motor starts without reversing if the DC motor 4 is in coasting.

Figure 2 shows an example of a timing chart for starting when the motor is stopped due to engagement. The power switch controls starting and stopping the motor. PWR-SW is the power switch, and MOTOR is the motor output. The bottom line is the number of on cycles. The RUN-SW, DIR-SW, and FG that were previously required have been omitted because they are no longer necessary.

In ON cycle 1, since the DC motor 4 is stopped when the power is turned on, the rotation direction information up to that point, for example, the CW direction (clockwise direction), is reversed and the motor starts in the CCW direction (counterclockwise direction).
ON cycle 2 illustrates an example in which jamming occurs midway and the DC motor 4 stops rotating. At start-up, the rotation direction CCW in ON cycle 1 is reversed and the motor starts rotating CW. Because jamming occurred during CW rotation and the motor stopped, the protection circuit operates and cuts off the coil current, and the operator turns off the PWR-SW, completing ON cycle 2.
On cycle 3 indicates that the DC motor 4 is stopped when the power is turned on, so the rotation direction information CW up until that point is reversed and the motor starts in the CCW direction. The motor starts in the reverse direction and the engagement is released.
Operating the rotation command switch when a jamming stop occurs is a natural operation, and this improves operability and work efficiency.
Furthermore, unintended operations by the operator, such as automatic reversal start by the control program of the control circuit or repeated start and stop by a timer as in conventional methods, are not performed, so there is no risk of the blade moving on its own while the workpiece is being removed by hand, and safety is also high.
In addition, since the direction of rotation is reversed for each ON cycle, uneven wear of the mechanism and problems with the brushes of brushed motors are also eliminated.

Next, the reason for storing the rotation direction information in the non-volatile memory 16 (EEPROM) built into the control circuit 13 will be explained. In bidirectional operation, if the power switch 11 (PWR-SW) is momentarily turned off and then immediately turned on while the motor is rotating, the DC motor 4 will be rotating by inertia when the power is turned back on, and if it is started in the reverse direction, the reverse brake will be applied, causing a shock and possibly damaging the mechanism and circuit. Therefore, if the motor was rotating by inertia when the power was turned on, it must be started in the same direction as the inertia.
In addition, if the rotation direction information is stored in a volatile memory such as a random access memory (RAM), it will be reset to the default value when the power is turned on, so the motor will always start in forward rotation. Therefore, if an instantaneous off operation is performed while the motor is rotating in the reverse direction, the DC motor 4 will naturally coast in the reverse direction, and the drive circuit will be reset as the power supply is momentarily cut off, switching it to a forward rotation start, and the reverse brake will be applied.

Therefore, a non-volatile memory 16 such as an EEPROM or flash memory is provided, and the rotation direction information is stored in the non-volatile memory 16 and is not reset when the power is turned on. By using the non-volatile memory 16, the previous rotation direction information is stored even if the power switch 11 is turned off. Therefore, for example, when the power switch 11 is turned off momentarily while rotating in the CCW direction, the DC motor 4 starts rotating in the CCW direction, which is the previous rotation direction, and since the DC motor 4 is naturally rotating in the CCW direction by inertia when the power switch is off, the rotation direction when the power switch is turned on matches, and no reverse braking occurs, smooth rotation continues, and there is no risk of damaging the mechanism or circuitry.

Figure 3 shows a timing chart for instantaneous off operation using non-volatile memory 16. PWR-SW is the power switch 11, CUR is the coil current, and MOTOR is the motor output. The bottom line is the number of on cycles. The RUN-SW, DIR-SW, and FG that were previously required are no longer necessary and have been omitted. The operation for each on cycle is explained below.

In ON cycle 1, since the motor is stopped when the power is turned on, the rotation direction information up to that point, for example, the CW direction, is reversed and the motor starts in the CCW direction.
On cycle 2 is an example of an instantaneous off operation that is turned on after a short off period. When the power is turned on, the motor rotates in the CCW direction by inertia and this is detected, so the direction of rotation is not reversed. The previous rotation direction information, CCW, is applied as is and the motor starts in the CCW direction. Since the inertia rotation direction and the current direction are the same, reverse braking does not occur. Note that the coil current waveform RB in the coil current CUR column is shown by a dashed line when reverse braking occurs. During reverse braking, an induced voltage is superimposed on the power supply voltage, so a large brake current flows, which may damage the circuit, battery, or mechanism.
In ON cycle 3, since the motor is stopped when the power is turned on, the rotation direction information CCW up until that point is inverted, indicating that the motor has started rotating in the CW direction.
In this way, even if the power switch 11 is momentarily turned off, reverse braking is avoided and the cutting operation continues smoothly, thereby ensuring safety.

Next, we will explain how to control the current supply to the motor using the rotation command switch 17. When using a high-current DC motor 4, starting and stopping it with the power switch 11 requires the use of a switch with a large contact capacity, which is unreasonable. Therefore, it is possible to keep the drive circuit 12 constantly energized and provide a separate rotation command switch 17, input a rotation command to the control circuit 13, and control the current supply to the DC motor 4 by controlling the output circuit 14 using the rotation command. In this way, it is possible to control the current supply to a high-current motor using a small-capacity switch. However, this method has the disadvantage that the circuit current of the drive circuit is constantly consumed.

Therefore, if power is constantly supplied to the drive circuit 12 and the control circuit 13 is configured as a microcontroller (MPU) with a sleep function, and a rotation command is issued to switch from sleep mode to wake-up mode, and the motor's rotation state is detected in wake-up mode to start the motor, the power switch 11 can be omitted. Sleep mode is a function provided in the microcontroller that stops operation by itself, reduces power consumption, and goes into a standby state, and when necessary, a wake-up signal is given from outside and the control program starts operation.

Fig. 4 shows a block diagram of the motor drive circuit 3 equipped with a rotation command switch 17. The reference numerals in Fig. 10 are used and explanations of the same reference numerals are omitted. Instead of the current control by the power switch 11 already described, a rotation command switch 17 (RUN-SW) is provided and a rotation command RUN signal is input to the control circuit 13 (MPU).
The microcontroller (MPU) is equipped with a non-volatile memory 16 (EEPROM) and stores the rotation direction information even during a power outage or in sleep mode. By utilizing the sleep function of the microcontroller (MPU), the control circuit 13 transitions from sleep mode to wake-up mode in response to a rotation command RUN signal, and the power switch 11 is omitted. The timing chart can be seen in Figure 2 or Figure 3, and the power switch 11 (PWR-SW) can be regarded as the rotation command switch 17 (RUN-SW).

As a result, when a rotation command is input from the rotation command switch 17 (RUN-SW) to the control circuit 13, the microcontroller (MPU) switches from sleep mode to wake-up mode based on the input rotation command and energizes the drive circuit 12 in wake-up mode, and at this timing the control circuit 13 can detect the rotation state of the motor and execute a start-up routine. In other words, it can be used with the drive circuit 12 energized, and the power switch can be omitted and it can be started only by the rotation command switch 17 (RUN-SW). Also, when the motor stops, the drive circuit 12 goes into sleep mode, consuming almost no power and saving energy. If you want to cut off the power supply, you can simply remove the battery 2 from the exterior case 1 (see Figure 1).

A three-phase brushless DC motor may be used instead of the three-phase brushed DC motor as the DC motor 4. In this case, the H-bridge circuit of the drive circuit 12 (DRIVER) may be replaced with a three-phase inverter circuit, and a position sensor signal such as a Hall IC may be input to the control circuit 13.
The electric cutting tool can be suitably applied to tools such as hedge trimmers, reciprocating saws, and clippers, in which the cutting part 7 reciprocates or swings in response to the rotation of the DC motor 4.

1 Outer case 2 Battery 3 Motor drive circuit 4 DC motor 4a Motor case 4b Stator magnet 4c Brush 4d Rolling bearing 5 Motor shaft 5a Rotor core 5b Coil 5c Commutator 6 Cutting blade 7 Cutting section 11 Power switch (PWR-SW) 12 Drive circuit (DRIVER) 13 Control circuit (MPU) 13a Rotation state detection section 14 Output circuit (INV) 15 Coil current sensor 16 Non-volatile memory 17 Rotation command switch (RUN-SW) 20 Eccentric cam 20a Cam section

Claims (3)

An electric cutting tool in which a cutting part having cutting blades on both sides in a forward and backward directions is reciprocated by a DC motor,
a drive circuit capable of rotating a DC motor that drives the cutting unit in a forward and reverse direction;
a rotation command input unit that outputs a rotation command to the drive circuit,
The drive circuit includes:
a rotation state detection unit that detects a rotation state of a motor in response to an input from the rotation command input unit;
a rotation direction storage unit having a non-volatile memory that retains information on the rotation direction of the motor even when the power supply to the drive circuit is cut off;
a control circuit having a gate output unit that outputs a gate signal according to the rotation direction of the motor;
an output circuit that energizes the DC motor through an output element group in response to a gate signal output from the gate output unit,
when a rotation command is input from the rotation command input unit , the rotation state of the motor is detected by the rotation state detection unit , the rotation state detection unit measures the coil voltage in a non-energized state to detect an induced voltage or detects a period of a rotation sensor signal, and if the control circuit determines from the detection results that the motor is rotating, it holds the rotation direction information stored in the rotation direction memory unit without changing it, and if it determines that the motor is stopped, it rewrites the rotation direction information stored in the rotation direction memory unit so as to invert it and executes a start-up routine, determines the rotation direction of the motor in accordance with the rotation direction information stored in the rotation direction memory unit, and outputs a gate signal from the gate output unit to energize the DC motor via the output circuit, thereby starting it. The electric cutting tool according to claim 1, wherein the control circuit detects the rotation state of the motor and executes a start-up routine when power is supplied to the drive circuit. An electric cutting tool according to claim 1 or 2, in which a DC power supply is constantly applied to the drive circuit, the control circuit is in a sleep mode in which the microcontroller is in a standby state, and when a rotation command is input from the rotation command input unit to the control circuit, the microcontroller switches from the sleep mode to a wake-up mode based on the input rotation command, and when the control circuit switches to the wake-up mode, it detects the rotation state of the motor and executes a start-up routine.