JPH09277195A - Control method of power tool and control circuit thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control method of a power tool and a control circuit thereof which is heightened in anti-kick-back technique so that the operation which can be completed by an operator can be continued without interruption. SOLUTION: A sudden rise in motor current di/dt exceeding a specified threshold value brings a motor control device into pulse mode operation. In the pulse mode operation the pulse current to the motor is suddenly inputted or outputted in order to remove an obstruction or restraining conditions of a work, which lead to motor stall. When the obstruction or restraining conditions of the work are removed, the motor starts an ordinary mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electrically driven power tools, and more particularly to pulse motors to overcome motor stall (eg kickback or breakthrough) conditions. The present invention relates to a control method and a control circuit for a power tool motor for detecting and responding to the start of a motor stall condition by supplying an electric current.

[0002]

BACKGROUND OF THE INVENTION Power tools typically use a motor that torques the tool via a rotating shaft. In the case of electric drills, the rotating shaft of the motor is connected to the chuck part through a series of reduction gears, which in turn grip other cutting or polishing tools such as drill bits or hole saws, grinding wheels, etc. . A power screwdriver having a chuck portion that holds a screwdriver bit operates on the same principle. In both cases, the ability to reduce gears or gear trains increases the rotational torque of the tool while reducing the rotational speed of the tool.

Power routers (such as round chisel tools) are somewhat different. A typical handheld router cutting tool (router bit) is typically directly coupled to the rotary shaft of a motor. Thus, to rotate the router bit at high speed, the full rotational speed or RPM of the motor is used without gear reduction. The use of reciprocating saws and jigsaws uses other types of gear trains to translate the rotational movement of the motor's rotating shaft to reciprocate.

In general, these power tools encounter sudden (immediately) stalling conditions that are about to stop, at which time local changes in the hardness of the work piece, binding or clogging of the work piece, and scoring ( The output torque rises sharply due to tool obstacles caused by burrs. If the cause of this condition is not overcome, the tool will jam and the motor will stall. When drilling a hole with a power drill, for example, there are workpieces that produce burrs on the tool exit side, these burrs collect in the flutes of the drill bit and the torque rises sharply when the drill bit is released from restraint. To do. In some cases, especially in metal workpieces, the burr actually stops the rotation of the drill bit and the motor rotates the tool in the operator's hand (instead of rotating the drill bit), thus manipulating the tool. A strong reaction torque will be applied to the person.

A related phenomenon occurs in power saws. Quoted as kickback, the saw blade cutting movement is often partially or wholly blocked by the workpiece when the saw is nearing completion and when the unsupported workpiece immobilizes the saw blade. is there. When the movement of the saw blade is disturbed, a large motor torque is generated, and in some cases the motor actually stalls.

[0006] These conditions are generally referred to below as "kickback" or "stall" conditions, regardless of the special power tools or special circumstances that result in kickback or stall conditions that are about to stop.

The assignee of the present application has previously detected (immediately) kickback conditions that are about to stop, inhibit the powering of the tool, and / or respond to imminent kickback conditions. We have developed an anti-kickback power tool control technology that applies additional braking to the tool. These systems are described in US Pat. Nos. 4,267,914 and 198 issued to Saar entitled "Anti-Kickback Power Tool Control", issued May 19, 1981.
It is described in detail in U.S. Pat. No. 4,249,117 issued to Leukhardt et al. Entitled "Anti-Kickback Power Tool Control", issued February 3, 1st. The anti-kickback control system described in these patent documents,
It is designed to interrupt the power to the motor once an imminent kickback condition occurs. In order to re-power the tool, the trigger switch must either be fully released and then retracted or some other signal must be provided by the operator.

[0008]

However, although the systems described in these patent documents are effective in detecting and preventing the kickback condition, the kickback condition of the control circuit disclosed in these patent documents is not effective. Responses that hinder the ability of the operator to accomplish the desired task. That is, the work that can be completed by the operator is interrupted.
For example, when power is interrupted by a burr-tightened drill bit that is formed during a breakthrough, the operator may not be able to re-interrupt power to the motor without repeating stall conditions. It is difficult to destroy the burr and complete the drilling so that it completely eliminates the burr. As a result, the anti-kickback described in the above patent document is effective not only for detecting and preventing the kickback condition, but also for helping the operator overcome obstacles and complete the intended work. It is necessary to improve the technology.

Therefore, the present invention aims to improve the applicant's anti-kickback technology which is prior art.

[0010]

Instead of responding to a kickback condition that is about to stop (immediately) by simply interrupting (and / or braking) power to the tool, the present invention provides many In that case, enable manipulation of the pulse input to the motor that can actually analyze or account for breakthrough or kickback conditions so that the tool does not have to stop and restart. When the present invention is used with a power drill, for example, the controller of the present invention detects an impending stall (eg, kickback or breakthrough) condition and pulses the motor for a predetermined period of time to deliver a series of torque pulses. Allows the user to hold the trigger switch in the actuated side while responding to the condition. Each of these torque pulses has a peak torque that is substantially greater than the average torque delivered during the series of pulse deliveries. The impact of these torque pulses allows the tool to break through (burst) through flash or work piece limitations that cause imminent stall or kickback conditions. In one embodiment, the pulses are delivered in a sequence arranged to be matched in relation to the characteristic frequency of the power tool gear train. This causes the gear train to oscillate between an excited state and a non-excited state at the gear train's characteristic frequency, thereby providing an output even greater than the peak torque.

The present invention can be used with virtually any power driven tool. When integrated with the rotary saw motor control,
The pulsed input to the motor is effective in clearing the work piece jam, or in breaking the constraint that initially caused the imminent stall or kickback.

Accordingly, the present invention provides a method and circuit for controlling virtually any power tool having a motor in which torque is applied to the output rotary shaft of the motor when an operator actuable switch is actuated. The method of the present invention includes the step of detecting a parameter of the motor that indicates the start of a stall condition. The detected parameter may be the motor current, for example the onset of stall is inferred by monitoring the rate of change of the motor current over time. When the trigger switch remains activated, the motor is pulsed for a period of time to deliver a series of torque pulses. Here, each peak pulse has a peak torque substantially greater than the average torque transmitted during the series of torque pulses. In many cases, these torque pulses remove the condition that causes an imminent stall. When this condition is removed, then normal motor operation resumes. If this condition is not removed, the power to the motor is removed after a lapse of a predetermined time in order to avoid burnout of the motor.

The present invention is useful in a wide variety of power tools. Before describing the principle of the present invention, a power drill will be described in detail below with reference to the accompanying drawings. Also, it will be readily apparent from the following description that the present invention is equally applicable to other types of power tools. In order to more fully understand the present invention, the objects and advantages of the present invention will be described below with reference to the accompanying drawings.

[0014]

1 is a side view of a typical variable speed power drill in which the control circuit of the present invention may be used. In FIG. 1, reference numeral 10 indicates the entire power drill. Power drill 10 is integrally formed with control circuit 12 in accordance with the preferred embodiment of the present invention. The power drill 10 has a general structure, that is, a motor 16, a gear train (gear train) 20.
And a tool blade accommodating chuck 22. The trigger switch 24 controls the supply of current to the motor 16 and can be used to change the motor speed to suit various uses of the power drill 10. The drill blade 26 is mounted within the tool blade receiving chuck 22 as shown. The drill blade 26 has a general configuration of flutedshank.
It has a (groove portion) 28 and a cutting tip portion (blade edge) 30.

FIG. 2 is a block diagram schematically showing a preferred embodiment of the control circuit of the present invention. The control circuit 12 supplies current to the motor 16 for both normal (continuous) and pulse mode operation in accordance with the present invention. Control circuit 12
Has a small controller 30 which is a microprocessor or a microcomputer. Power supply circuit 3
2 is connected to the AC (alternating current) power supply line input and supplies an appropriate DC (direct current) voltage for operating the small controller 30. As shown, the trigger switch 24
Supplies a trigger signal to the compact controller 30. The trigger signal indicates the position or setting of the trigger switch when the trigger switch is being manually operated by the operator of the tool. If required, the miniature controller 30 may also include a reset circuit 34 that reinitializes the miniature controller 30 when activated.

The drive current for operating the motor 16 is controlled by a triac (trademark, gate control type semiconductor switch) drive circuit 36. The triac drive circuit 36 is in turn controlled by signals provided by the small controller 30. The current sensor 38 is the motor 16
And is connected in series to the triac drive circuit 36. The current sensor 38 can be, for example, a low resistance, high wattage resistor. The voltage drop of the current sensor 38 can be measured as an indication of the actual motor instantaneous current. The instantaneous current is measured in this way, and the average current measuring circuit 40
The average current measuring circuit 40 in turn supplies the average current value to the small controller 30. Small controller 30 uses the average current to evaluate whether to switch to or from pulse mode operation. In addition to the average current, the small controller 30 is supplied with a signal from the current detection circuit 42. Current detection circuit 4
2 is connected to the triac drive circuit 36 and supplies a signal indicating that the triac drive circuit 36 is in a conductive state. If, for some reason, the triac did not turn on in response to the control signal from the miniature controller 30, the current sensing circuit 42 would detect this and reduce this so that another control signal could be sent by the miniature controller 30. Notify the controller 30. In particular, when the gate voltage of the triac is 0 (the triac is in a non-conducting state), the current detection circuit 42 supplies a signal indicating this state to the small controller 30.

In operation, the trigger switch 24 provides the small controller 30 with a trigger signal that varies proportionally to the switch setting. Based on this trigger signal, the small controller 30 generates a control signal for causing the triac drive circuit 36 to conduct, thereby allowing a current to flow to the motor 16. The motor current that rotates this motor is approximately proportional to the motor torque. Average current measurement circuit 40 and current sensor 38 monitor the motor current and provide an average current signal to small controller 30. This average current signal is processed by the small controller 30 to detect when an impending stall condition has occurred, as described below. When a urgent stall condition is detected, the small controller 30
Switches to pulse mode operation and supplies abrupt on / off current pulses to the motor 16 to the triac drive circuit 36. These current pulses provide a series of torque pulses each having a peak torque that is substantially greater than the average torque delivered during pulse mode operation. In many cases, these torque pulses clear the conditions that cause abrupt installation. If so, that is, if the condition causing this installation is removed, then the small controller 30 detects the release of this condition by monitoring this average AC and automatically returns to normal motor operation. .

The pulse mode operation of the present invention can be implemented by various processes executed by a microprocessor. Two processes will be described below. The first process is shown in FIG.
And the second process is shown in FIG. FIG. 10 shows details of the AC power drill motor control circuit. further,
The details of one possible pulse mode routine, the pseudocode routine, are given below.

Pulse mode routine Initialization of current on time Initialization of current off time Initialization of duration of pulse mode Initialization of current threshold Initialization of pulse mode duration counter Start while pulse mode duration is not elapsed [On time As a pulse input to the motor] Current on-time counter start While current on-time counter has not elapsed Turn on current Measure motor average current When motor average current is lower than current threshold Move to motor pulse routine [When stall is released Early transition] In other cases, when the switch is open, shifts to the motor pulse routine [When switch is open, shifts to early] In other cases, it ends, while [motor pulse input on / off time] Current turn-off current off time Counter start Current off time When, the motor pulse routine is entered [earlier when the switch is open] ends, while [the above is repeated until the pulse mode duration elapses] the motor power supply is turned off and the trigger switch lockout (physical reset position) Until end

FIG. 3 is a flow chart of a motor control routine according to the first embodiment of the present invention. This routine starts at step 100, and at step 102 it is determined whether or not the operation switch is closed. This operating switch may be, for example, a manually operated trigger switch 24 of a power drill. When the operation switch is not closed, the power to the motor is cut off (step 104),
Return to step 102. When the operating switch is closed, power is supplied to the motor (step 106) and the motor conducts current in proportion to the load applied to the motor by the tool. The motor current is monitored (step 10
8) The rate of change of motor current is measured (step 11
0). When the rate of change of the motor current is positive (step 11
2) and when the rate of change of motor current exceeds a predetermined threshold (step 114), the pulse routine is called (step 116). When the rate of change of the motor current is not positive or the rate of change of the motor current does not exceed the predetermined threshold, the control routine returns to step 102.

FIG. 4 is a time chart of a pulse mode useful for understanding the present invention. The pulse mode routine can be implemented by various processes executed by the microprocessor. The pseudo code routine above illustrates an example of such a process. With reference to this fake code routine,
This process defines a current on time and a current off time.
These times are used to generate the motor current pulse waveform shown in FIG. If desired, the on-time and off-time can be equal (duty ratio 50%) and other duty ratios may be used. In some embodiments, the on and off times are derived from the frequency of the AC power line.
Alternatively, the on-time and off-time can be generated by a clock mounted on the small controller 30. With proper choice of on-time and off-time, the frequency of the pulsed current signal can be set during system design.

Although the present invention can be implemented in various combinations of on-time and off-time, it is advantageous to select the on-time and off-time corresponding to the resonance frequency of the gear train of the tool. Power tool gear trains typically have some degree of backlash (play) that causes the motor spindle to rotate between an excited position where power is applied to the motor and a non-excited position where power is removed. It is possible. In many physical systems, it has a resonance frequency that is characteristic of the motor and its gear train, that is, the frequency at which vibrations most naturally occur between excited and de-energized states. When a pulsed current is applied synchronously with this natural frequency, the vibrational energy is enhanced. To illustrate this principle, consider how a basketball is dribbled by applying energy by hand at or near the top of each bounce in synchronization with the bounce frequency. Energy is applied at appropriate times such that vibrations (rebounds) are enhanced. Energy can be applied to this oscillating gear train system in much the same way.

The characteristic resonant frequency of the power tool gear train can be measured empirically using the procedure described in Pseudo Code shown in the Pseudo Code Routine above. To detect the characteristic resonant frequency, the microcontroller is programmed to iteratively select various on and off time ranges while the torque output of the tool is measured. The on-time and off-time values corresponding to these maximum torque outputs correspond to the characteristic resonant frequencies of the gear train system (or their harmonics, if any).

Referring to the bogus code listing shown in the bogus code routine, this process also defines the duration of the pulse mode. As also shown in FIG. 4, the duration of the pulse mode is a predetermined time that runs when the pulse mode routine is called. The preferred embodiment of the present invention terminates the pulse mode routine under certain conditions after the pulse duration of the pulse mode has elapsed. Thus, if the stall condition is not removed within the pulse duration of the predefined pulse mode, the motor will stop to avoid burnout.

The processing of the false code also defines the current threshold at which the pulse mode routine can terminate because the imminent stall condition has been cleared. This process starts by initializing the above values. The pulse duration counter in pulse mode is then started. The rest of the routine is executed until the pulse duration counter in the pulse mode elapses (counts up).

The motor current is turned on while commanded by the current on time. This is accomplished by starting the current on-time counter and then turning on the motor current until the current on-time counter expires. While the motor current is turning on, the current sensing system measures the average motor current. Preferably, this measurement is done on a cycle-by-cycle basis using the circuit described above. When the average motor current is less than the initialized current threshold, the motor pulse routine ends prematurely. Also, when the operator opens the switch when the current-on timer has not elapsed, the motor pulse routine ends.

The off-timer is measured after the on-timer has elapsed. The motor current is turned off and the current off time counter starts. The routine monitors to see if the operator has opened this switch until the current off time counter has expired. When the result of this monitor is YES, the motor pulse routine ends. After the motor off time has elapsed, control branches back to the on time segment of the process so that the cycle repeats until the pulse duration of the pulse mode has elapsed.

When the pulse duration counter in pulse mode has expired, one condition is reached only if the stall condition is not cleared, the power to the motor is switched off, the brake is applied and, if desired, the operation. The trigger switch is locked out until it is physically reset by the operator.

FIG. 5 is a flow chart of a motor control routine according to the second embodiment of the present invention. The routine begins at step 130 and at step 132 first measures the movement of the trigger to measure the current setting of the trigger switch 24. The switch 134 then measures the average motor current and the switch 136 sets the voltage applied to the motor in proportion to the movement of the trigger. In this way, the motor is set to operate at the speed commanded by the setting of the trigger.

In the second embodiment shown in FIG. 5, pulse mode operation is only performed when the change in travel or movement of the trigger is greater than a predetermined threshold. Therefore, in step 138, the change in trigger movement is compared to the delta trigger threshold. When the change in trigger movement is not greater than the threshold, control simply returns to step 132. In other cases,
Control proceeds to step 140, where the absolute current is compared to the absolute current threshold. When the absolute value of the current is greater than the current threshold, pulse mode operation is initiated (step 142). When the absolute current is less than or equal to the current threshold, control proceeds to step 144 and the rate of change in average current over time is analyzed. Pulse mode operation is initiated (step 142) when the time change in average current (di / dt) is greater than an upper threshold or greater than an intermediate threshold over two consecutive cycles. If none of these tests are satisfied, control returns to 132 (step 144).

The motor remains in pulse mode operation until some event occurs. As shown in steps 146 and 148, the motor is stopped when the average current is greater than the upper threshold during pulse mode operation. Also, when the average current is less than the lower threshold as shown in step 150, pulse mode operation is terminated and control proceeds to step 1
Return to 32.

FIG. 6 is a diagram showing the motor current as a function of time showing the method of controlling the motor in the normal mode operation and the pulse mode operation. FIG. 6 illustrates, as another example, the motor current of the power drill equipped in the present invention. Motor torque is proportional to motor current.
Therefore, the depiction in FIG. 6 also shows how the motor torque is controlled. When the tool is switched on, it accelerates to full speed and the motor current rises sharply as shown at A in the figure. After that, the motor current settles to the normal operation current as shown by B in the figure. When the work piece is drilled, the motor current fluctuates slightly up and down depending on the hardness of the work piece and the applied force of the operator. In addition to these small changes, the motor current is approximately constant as the drill bit advances into the workpiece as shown in inset I of FIG.

When a breakthrough occurs, the motor current sharply rises as shown in C in the figure as shown in the inset II. In particular, the rate of change in the motor current is steeper than during the initial acceleration shown by A in the figure. The reason for this sudden increase in motor current is that the holes on the exit side of the work piece are not perfectly round and can have irremovable material in the burrs or drill bit grooves. .

When a rapid rise in motor current is detected by the present invention, the pulse mode routine is called and the motor current flows in pulses, as shown at D in the figure. The peak of the motor current (torque) that occurs during this pulse mode operation is the average motor current (torque) during this period.
It should be noted that it is substantially larger. Peak motor current and peak torque are also substantially greater than average torque during normal drilling, as shown at B in the figure. It should also be noted that the peak current reaching the maximum value in E in the figure decreases with successive peaks. Finally, the peak current drops to the threshold current at F in the figure, where normal (non-pulsed) operation is resumed.

While each pulse current is flowing in the pulse operation mode, the cutting end of the drill bit is left uncut like a chisel (only chisel) or a burr (burr). Driven to collide with the workpiece. After each crash, the gear train is allowed to release, allowing the cutting end of the drill bit to retract slightly for the next crash. In this way, the cutting end of the drill bit enables chopping motion,
The peak torque generated during each chop is substantially greater than the average torque that the motor could otherwise provide. This pulsing action allows the tool to break through burrs or other material obstructions left behind. After this breakthrough occurs, the tool resumes normal operation, so the hole can be further cleaned as shown in inset III. The pulsed operation also alerts the operator that the above conditions have occurred.

Obviously, the trigger switch remains on, ie activated by the tool operator, during this full pulse operation. The system will automatically enter pulse mode operation when a sudden rise in motor current is commanded, and the operator can simply keep the trigger switch closed while concentrating on the drill or cutting operation. it can.

When the pulse mode operation cannot overcome the stall condition, the motor is stopped after the pulse duration of the predetermined pulse mode has elapsed.

Although a drill bit is shown by insets I-III in FIG. 6, the present invention is also useful with other types of power tools as described above. In the case of power saws, potential stall conditions can occur after cutting is complete. The stripped material then jams between the saw blade and the rip fence or other guide. The actuation of pulses in pulse mode operation often vibrates the unobstructed workpiece and also alerts the operator to this condition. Thus, the present invention is applicable to a wide range of power tools including drills and saws.

A more detailed understanding of the motor control routine shown in FIG. 5 is described below with reference to FIGS. 7, 8 and 9. These figures show the average current of the motor as a function of time (measured in line cycles) (small controller 30
A / D output by the analog / digital conversion circuit of
Conversion value).

The preferred embodiment of FIG. 5 shows an example of performing pulse mode operation synchronized to the AC line frequency. In the false code listing above, a more generalized case is shown where pulse mode operation is not necessarily synchronized to line frequency. In the fake code list, the on / off time can be any value measured by the clock circuit of the microprocessor. In the embodiment shown in FIGS. 7-9, the on / off time is measured by counting a predetermined number of AC cycles instead of using the clock circuit of the microprocessor. For AC power tools,
The embodiment of Figures 7-9 is preferred. For DC-powered power tools, such as cordless battery-powered power tools, the microprocessor clock-based embodiment can be used.

FIG. 7 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention. FIG. 7 shows an example of the operation of the system of FIG. After the switch is turned on as shown by A in the figure, the average current of the motor settles at a stable operation value as shown by B in the figure. This current indicates normal tool operation without imminent stall conditions. At C in the figure, the current sharply rises, indicating an imminent stall condition. As shown in FIG. 5, the imminent stall condition occurs when one of the following two conditions is satisfied. Condition 1: The average motor current as a function of time is greater than a predetermined delta threshold. FIG. 7 shows this delta threshold as the rate of change or the value of the first derivative corresponding to a predetermined rate of current rise or slope. Condition 2: The average current of the motor exceeds the threshold of absolute value.
FIG. 7 shows the absolute threshold as the current exceeds the lower threshold shown. When these two conditions are met once (in this case, the first condition is met), pulse mode operation is initiated. When the cause of the imminent stalling condition is not clear after a predetermined time (after the predetermined number of line cycles have been counted), the motor is stopped, as indicated by G in the figure. Stopping occurs in this case because the average current exceeds the upper threshold.

FIG. 8 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention. FIG. 8 shows that the motor current enters pulse mode operation as indicated by C in the figure and then returns to normal operation as indicated by F in the figure. Normal operation is resumed as the motor current drops below the lower threshold.

FIG. 9 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention. FIG. 9 shows a case where the pulse mode operation is started as shown by C in the figure and this mode is continued without calling the stop of the motor. The peak current of this motor drops below the upper current threshold during pulse mode operation. This is because the upper threshold is not reached and pulse mode operation continues. When FIG. 9 is compared with FIG. 7, the peak of the average current in FIG. 7 exceeds the upper limit threshold during the pulse mode operation. Therefore, in FIG. 7, pulse mode operation is terminated and the motor is stopped at G in the figure, while in FIG. 9 pulse mode is not terminated.

FIG. 10 is a detailed electrical schematic diagram of a motor control circuit in an embodiment for an AC power drill of the present invention.
The group of components in the embodiment of FIG. 10 corresponds to the components of the block diagram of FIG. Therefore, reference can be made to FIG. 2 for an overview of the function of the components of these circuits. Referring to FIG. 10, a preferred power supply circuit 3 for power of the present invention
2 uses Zener diodes to supply low voltage power supply voltages including 5 VDC and 12 VDC to various parts of the circuit.

The circuit of FIG. 10 can be constructed using a small controller circuit ST6210A connected by the pinout shown. Resonator 200 holds the appropriate clock frequency for small controller 30. Trigger switch circuit 2
4 is connected to the A / D input pin 10 of the small controller 30. The compact controller 30 can therefore monitor the setting of the trigger switch. AC line frequency is a detection resistor 2 connected to high impedance input pin 8
It is supplied to the small controller 30 via 02. It supplies a signal to the miniature controller 30 from which the AC line frequency can be obtained for synchronization and for generating a time base controlling the ratio of pulse mode operation.

Under certain conditions, the miniature controller 30 powers off the LEDs for optical display. Small controller 30 therefore provides a signal on pin 12 which is provided to the base of transistor 204. Therefore, the miniature controller 30 can monitor the status of the TRIAC drive circuit in which pin 15 is connected to the DC 5V power supply through the pull-up resistor 206. Pin 15 is also connected to the trigger terminal of triac 36 via resistor 208.
Due to the triac state, pin 15 of the miniature controller 30 is held low, thereby signaling a change in the state of the triac drive circuit.

The small controller 30 controls the operation of the triac drive circuit 36 via the pin 19. Pin 19
Is connected to the base of a transistor 212 for the triac drive circuit. A variable duty cycle AC signal is applied to transistor 212, which in turn activates the triac. The triac is connected to the neutral (ground) side of the motor circuit as shown.

As the motor operates, motor current flows through the current sense resistor 38. The current detection resistor 38 preferably has a low resistance (0.01Ω) and a high output. The voltage drop across the current sense resistor 38 is measured by the average current monitor circuit 40. The output of the average current monitor circuit 40 is supplied to the A / D input pin 11 of the small controller 30. This signal is used to determine when to turn on and off pulse mode operation and when to shut off power to the motor.

The preferred average current monitor circuit 40 of the present invention performs cycle-based average current measurements.
The operational amplifier 214 mirrors (reflects) the voltage drop obtained by measuring the current detection resistor 38. This reflected voltage is supplied to the base of transistor 216 and draws current through capacitor 218 to hold the voltage set by the values of transistor 216 and resistor 220. The cycle motor current i _ave can be calculated from the voltage V _c on capacitor 218 using the following equation: Here, R _s is the resistance value of the resistor 38, R _i is the resistance value of the resistor 220, and T is the period of the AC line current (for example, 10).
msec). i _ave = (R _i C / R _s T) · V _c

The voltage V _c on capacitor 218 is determined by resistor 2
It is supplied to the A / D input pin 11 via 21. Once A / D conversion by the small controller is completed, pin 1
1 is set to a state of output high and capacitor 218 via resistor 221 resets the average current circuit of the cycle cycle to receive the next positive half cycle of current.
Discharges. By resetting the average current circuit,
Allows the system to measure the average current of the motor with the response time of the line cycle. This is important when accurately and instantaneously detecting a sudden increase in motor current.

From the above description, the present invention provides a motor control circuit and a control method which can be integrated with various power tools in order to detect an urgent stall condition and overcome the stall condition in some cases. By equipping the present invention, the power tool is easier to operate because the operator can concentrate on making accurate drills or cuts without worrying about stall conditions such as breakthrough stalls and kickback conditions. And it becomes convenient. As another advantage, when an urgent stall condition occurs, the pulsed operation of the present invention provides a burst of torque so that the stall condition is overcome, but the average torque remains low so the operator You will never feel this torque. The action of this pulse, however, serves as a warning to the operator that a potential stall condition exists. Therefore, the power tool equipped with the present invention is less likely to get caught in the operator's hand.

Although the preferred embodiment of the present invention has been described above, it can be understood that the present invention can be modified or altered within the scope of the claims of the present invention. For example, although the present invention was first disclosed for AC power drill applications, it is equally applicable to battery powered power tools.

[0053]

According to the present invention, when power is interrupted by a burr-constrained drill bit formed during breakthrough, the motor is re-interrupted without repeating stall conditions. It allows the operator to break the burr and complete the drilling without interruption, so as to eliminate the burr completely from the hole, i.e. not only useful for detecting and blocking kickback conditions. A control method and a control circuit for a power tool having a motor that is effective for an operator to overcome obstacles and complete an intended work can be provided.

[Brief description of drawings]

FIG. 1 is a side view of a typical variable speed power drill that can use the control circuit of the present invention.

FIG. 2 is a block diagram schematically showing a preferred embodiment of the control circuit of the present invention.

FIG. 3 is a flowchart of a motor control routine according to the first embodiment of the present invention.

FIG. 4 is a time chart of a pulse mode useful for understanding the present invention.

FIG. 5 is a flowchart of a motor control routine according to a second embodiment of the present invention.

FIG. 6 is a diagram showing motor current as a function of time showing a method of controlling a motor in normal mode operation and pulse mode operation.

FIG. 7 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention.

FIG. 8 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention.

FIG. 9 is a diagram showing a motor current (digital value) as a time function (line cycle) useful for understanding the operation of the present invention.

FIG. 10 is a detailed electrical schematic of a motor control circuit in an embodiment for an AC power drill of the present invention.

[Explanation of symbols]

 10 ... Power drill 12 ... Control circuit 16 ... Motor 20 ... Gear train 22 ... Tool blade accommodating chuck 24 ... Trigger switch 26 ... Drill blade 28 ... Groove 30 ... Cutting tip (blade tip)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Paul G. Huber United States, Maryland 21131, Hornix, Manor Road 14710 (72) Inventor Fargan Patel, Maryland 21009, Abingdon, Cheberley Court 3337

Claims (21)

[Claims] 1. A method of controlling a power tool having a motor in which a torque is applied to an output rotary shaft of the motor when actuated by a switch operable by an operator, wherein a motor parameter indicating the start of an imminent stall condition is set. Detecting and pulsing a series of torque pulses to the motor a plurality of times having a peak torque substantially greater than the average torque transmitted while the torque pulse is continuously supplied when the switch remains activated. A method for controlling a power tool, characterized by: 2. The method of controlling a power tool of claim 1, wherein the drill is controlled under breakthrough conditions further comprising the use of the detected motor parameter as an indication of the start of breakthrough. 3. The method of controlling a power tool of claim 1, wherein the saw is controlled under kickback conditions further comprising using the detected motor parameter as an indication of kickback condition. 4. The method for controlling a power tool according to claim 1, wherein the detected motor parameter is a motor current. 5. The method of controlling a power tool according to claim 1, wherein the step of detecting the motor parameter is executed by detecting a rapid increase in the motor current. 6. The method for controlling a power tool according to claim 1, wherein the motor is powered by an alternating current having a predetermined cycle frequency, and the step of detecting the motor parameter is repeatedly executed in synchronization with the cycle frequency. 7. The method for controlling a power tool according to claim 1, wherein the step of inputting pulses is executed by periodically interrupting a current flow to the motor. 8. The method of controlling a power tool of claim 1, wherein the step of pulsing is performed by interrupting the flow of current to the motor about 20 to 30 times per second. 9. The motor is powered by an alternating current of a predetermined cycle frequency, and the pulsing step is performed by synchronizing current flow to the motor in synchronization with the cycle frequency. 1. A method for controlling a power tool according to 1. 10. The method for controlling a power tool according to claim 1, further comprising the step of terminating the pulse input step when the detected parameter indicates an average torque equal to or less than a predetermined threshold. 11. The method further comprising the step of terminating the pulse inputting step and inhibiting power supply to the motor when the detected parameter indicates an average torque that exceeds a predetermined threshold within a predetermined time period. 1. A method for controlling a power tool according to 1. 12. The method of controlling a power tool according to claim 1, wherein the tool has a characteristic resonance frequency, and the step of pulse input is performed at a frequency substantially in harmony with the characteristic frequency. . 13. The method of controlling a power tool of claim 1, wherein the motor is powered by an alternating current and the motor parameter is detected by detecting the motor current at least once during each cycle of the alternating current. . 14. The control of a power tool according to claim 1, wherein the motor is powered by an alternating current and the motor parameters are detected by measuring the average motor current at least once during each cycle of the alternating current. Method. 15. A control circuit for a motor for an electric tool, the drive circuit being connected to the motor for controlling to supply an electric current to the motor, and the drive circuit being connected to the drive circuit to control the drive circuit. A processor for providing a processor output signal for controlling a motor current, a current detector connected to the drive circuit for detecting a parameter indicative of a motor current and connected to the processor for supplying a first processor input signal, The processor comprises first means for using the first processor input signal to detect an early stall condition, the processor providing a pulsed current to the motor in response to initiation of the detected stall condition. The control circuit further comprising second means for using the processor output signal for 16. An operator actuatable switch connected to the processor for providing a second processor input signal such that current is supplied to the motor.
16. The control circuit of claim 15, wherein the second means periodically overcomes the second processor input signal to inhibit the supply of current to the motor. 17. The control circuit according to claim 15, wherein the current detector detects an average motor current. 18. The motor is powered by an alternating current, and the current detector detects the average motor current at least once per cycle of the alternating current.
5. The control circuit according to item 5. 19. The control circuit according to claim 15, wherein the drive circuit includes a triac circuit that controls a speed of the motor. 20. The control circuit of claim 15, wherein the processor further comprises means for terminating the supply of current pulses to the motor after a predetermined time. 21. The processor includes means for using the first processor input signal to detect that the stall condition has been cleared, and to the motor in response to detecting that the stall condition has been cleared. Means for terminating the supply of the current pulse of
The control circuit according to claim 15, further comprising: