JPH09314482A - Torque control to prevent kick-back and penetration of electric tool - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control technology which is not only effective in detecting and preventing the kick-back condition but also capable of overcoming the tense kick-back condition and completing the intended work by an operator. SOLUTION: Rapid increase in the motor current (di/dt larger than the prescribed threshold) leads a motor control device into the pulse mode operation. In this pulse mode operation, the motor current is pulsed by rapidly turning-on/ turning-off the motor current to eliminate interference on a work or the binding condition in which a motor 16 is inoperable. When interference or binding of the work is cleared, the motor 16 re-starts its normal operation.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a power tool. More particularly, the present invention is directed to a motor control circuit and motor that detects the start of an immobile condition (eg, kickback or breakthrough condition) and responds to the immobile condition by pulsing the motor to overcome the immobile condition. Regarding control method.

[0002]

2. Description of the Related Art Generally, an electric power tool has a motor for transmitting torque to the tool via a spindle. In the case of electric drills, the motor spindle is connected to the chuck via a series of reduction gears, which holds the drill bit or other cutting or grinding tools such as hole saws, grinding wheels and the like. Electric screwdrivers operate on a similar principle, with the chuck holding the screwdriver bit. In both cases, the function of the reduction gear or reduction gear train is to reduce the rotational speed of the tool and at the same time increase the rotational torque.

The power transmission path is somewhat different. The cutting tool (router bit) of a typical handheld router is generally directly connected to the spindle of the motor. In this case, the maximum rotation speed of the motor, that is, RPM is used without gear reduction, and the router is rotated at a high speed.
Reciprocating saws and jigsaws use another type of gear train that converts the rotational movement of the motor spindle into a reciprocating movement.

In general, all of these power tools suddenly encounter an impending immobile condition, at which time a local change in work hardness, work binding.
Alternatively, a tool failure caused by galling, burrs, or the like causes the output torque to rapidly increase. If the cause of this situation is not eliminated, the tool will seize and the motor will stop. For example, when drilling with an electric drill,
Some workpieces produce burrs on the tool exit side which engage the grooves of the drill bit and sharply increase the torque as the drill bit attempts to rotate freely. In some cases (especially in the case of metal workpieces) the burr actually stops the rotation of the drill bit and causes a strong reaction torque. This reaction torque is transmitted to the tool operator's hand as the motor rotates the tool, rather than rotating the drill bit.

A similar phenomenon occurs in an electric saw. As is known as kickback, when the saw cut is about to complete and the unsupported work bites the saw blade, the cutting movement of the saw blade is often partially or completely blocked by the work. When the movement of the saw blade is disturbed, a large motor torque is generated and in some cases the motor actually stops.

Hereinafter, these states are collectively referred to as "kickback" or "stall" states, and these states are referred to as the specific power tool involved or the specific conditions that cause a tight kickback or immobile state. Will be called like this regardless of.

To date, the assignee of the present application has detected a tense kickback condition and, in response to this kickback condition, interrupts the transmission of power to the tool and / or optionally brakes the tool. Developed kickback prevention power tool control technology. These devices are based on Saar's Anti-Kickback Power Tool Contr
"Ol)" of U.S. Pat. No. 4,267,914 dated May 19, 1981 and Leukhardt et al. "Anti-Kickback Power Tool Control".
No. "US Patent No.
It is described in more detail in No. 4,249,117. The anti-kickback controls described in these U.S. patents are designed to shut off the power supply to the motor once a tension kickback condition occurs. To reapply power to the tool, the trigger switch must be fully released and then depressed again, or the operator must provide some other signal.

Although the devices described in these US patents are effective in detecting and preventing kickback conditions, the responsiveness of the control circuit disclosed herein to a stressed kickback condition determines the operator's desired work. Makes it impossible to complete. For example, when power is interrupted by the binding of the drill bit to the burr formed during penetration, the operator removes the burr without repeating the immobile condition and causing a re-interruption of the power supply to the motor. It is difficult to complete the hole by doing so.

[0009]

Therefore, it is not only effective in detecting and preventing the kickback state, but also effective in allowing the worker to overcome the tense kickback state and complete the intended work. Advanced control technology is required.

[0010]

SUMMARY OF THE INVENTION The present invention relates to an improvement of the prior art kickback prevention technique of the present applicant. In addition to responding to a tense kickback condition by simply disconnecting (and / or braking) power to the tool, the present invention allows the motor to be stopped so that the tool need not be stopped and restarted. A pulsing actuation can often be performed to actually resolve or clear the penetration or kickback condition. When using the present invention in, for example, an electric drill, the operator can keep the trigger switch activated while the controller of the present invention is
Responding to a condition of immobility (e.g. kickback or penetration) by detecting and pulsing the motor for a period of time to provide continuous torque pulses. Each of these torque pulses has a peak torque that is substantially greater than the average torque provided during the successive pulses. The impact of these torque pulses enables the tool to break through burrs or workpiece obstructions that cause a strained or kickback condition. In one embodiment, the pulses are provided in a sequence designed to be harmonically related to the natural frequency of the gear train of the power tool. This results in a fairly large peak torque output by vibrating the gear train between the biased and relaxed states at the natural frequency of the gear train.

The present invention can be used with virtually any power tool. When applied to the motor control of a rotary saw, the work is free of galling due to the effect of motor pulsing (i.e., the binding condition that initially caused the immobility or kickback condition was exceeded).

Accordingly, the present invention provides a method and apparatus for controlling virtually any power tool that includes a motor that transmits torque to an output spindle when actuated by an operator operable switch. The invention comprises the step of detecting a motor parameter which indicates the start of a stationary state. The detected parameter can be, for example, the motor current, and the onset of immobility can be inferred by monitoring the rate of change of the motor current over time. The motor is pulsed for a predetermined time while the switch is in the actuated state to provide continuous torque pulses. The continuous torque pulse has a peak torque that is substantially greater than the average torque provided during the continuous torque pulse. In many cases, these torque pulses clear the condition that caused the immobility. When the motor is cleared, normal motor operation is resumed. When the motor is not cleared, the electric power supplied to the motor is shut off after a predetermined time to prevent the motor from being burned.

[0013]

For a more complete understanding of the present invention, its objects and advantages, please refer to the following description and to the accompanying drawings.

The present invention is useful with a wide variety of power tools. To illustrate the principles of the present invention, an electric drill is illustrated and described. It will be readily appreciated that the present invention can be successfully applied to other types of power tools.

In FIG. 1, reference numeral 1 indicates the entire electric drill.
It is indicated by 0. The drill incorporates a control circuit 12 according to a preferred embodiment of the present invention. The drill 10 includes a motor 16 and a gear train 20 in a conventional manner.
And a tool bit receiving chuck 22. The trigger switch 24 is also used to control the supply of current to the motor and to change the motor speed to suit the various tasks required. The drill bit 26 can be attached to the chuck as shown. The drill bit has a conventionally shaped grooved shank 28 and cutting edge tip 30.

Referring to FIG. 2, a block diagram of the preferred embodiment of the control circuit 12 is shown. The control circuit 12 supplies current to the motor 16 and performs both normal operation (continuous operation) and pulse mode operation according to the present invention.

The control circuit 12 comprises a microcontroller 30 in the form of a microprocessor or microcomputer. A power supply circuit 32 for the AC power line
Are connected, and the power supply circuit 32 is connected to the microcontroller 3
Supply the appropriate DC voltage to activate 0. As shown, trigger switch 24 provides a trigger signal to microcontroller 30. This trigger signal indicates the position or setting of the trigger switch when the tool operator manually operates it. If desired, the microcontroller 30 can be provided with a reset circuit 34 to reconfigure the microcontroller when the switch is activated.

The drive current for operating the motor 16 is controlled by the triac drive circuit 36. The triac drive circuit is controlled by signals provided by the microcontroller 30. The current sensor 38 is the motor 16
And the triac drive circuit 36 are connected in series. The current sensor 38 can be composed of, for example, a low resistance / high wattage resistor. The voltage drop across the current sensor 38 is measured as an indication of the actual instantaneous motor current. The instantaneous motor current measured in this way is supplied to the average current measuring circuit 40, which supplies the average current value to the microcontroller 30. The microcontroller 30 uses the average current to evaluate whether to switch to (and from) pulse mode operation.
In addition to the average current, the microcontroller 30 is also supplied with a signal from the current detection circuit 42. This circuit 42 is connected to the triac drive circuit 36 and provides a signal indication of the conducting state of the triac drive circuit. If for any reason the triac drive circuit does not turn on in response to the control signal from the microcontroller 30, the circuit 42 will detect this and notify the microcontroller to send another control signal pulse. To do. More specifically, when the triac gate voltage is zero (when the triac is not conducting), the circuit 42 provides an indication of this condition to the microcontroller.

In operation, the trigger switch 24 provides a trigger signal to the microcontroller 30 that varies in proportion to the switch setting. Based on this trigger signal, the microcontroller 30 causes the triac drive circuit 36 to conduct, thereby causing current to flow in the motor 16. The motor current rotates the motor, and the motor current is approximately proportional to the motor torque. Average current circuit 40 and current sensor 38 monitor the motor current and output the average current signal to microcontroller 30.
To supply. This average current signal is processed by the microcontroller 30 as described below to detect when an immobility condition has occurred. Upon detection of an immobility condition, the microcontroller 30 switches to pulse mode operation, causing the TRIAC drive circuit 36 to supply a fast on / off current pulse to the motor 16. These current pulses provide continuous torque pulses, each torque pulse having a peak torque that is substantially greater than the average torque provided during pulse mode operation. In many cases, these torque pulses clear the condition that caused the immobility. In this case, the microcontroller 30 detects this by monitoring the average current signal and automatically returns to normal motor operation.

The pulse mode operation of the present invention is implemented by a variety of different microprocessor-implemented procedures. Here, two procedures, the first procedure shown in FIG. 3 and the second procedure shown in FIG. 5, will be described. A pseudocode routine detailing one possible pulse mode routine is given in the APPENDIX at the end. The details of the motor control circuit of the AC electric drill are shown in FIG. 10 and described below.

FIG. 3 shows the first motor control routine. Starting at start step 100, the routine first checks if the operator switch is closed (step 102). The operator switch is, for example, a manually operated trigger switch 2 of an electric drill.
4 can be configured. If the switch is not closed, power to the motor is shut off (step 104) and the control branch returns to step 102. Power is supplied to the motor when the operator switch is closed (step 1
06), a current flows through the motor in proportion to the load acting on the motor via the tool. The motor current is monitored (step 108) and the rate of change of the motor current is measured (step 110). When the rate of change of the motor current is positive (step 112) and the rate of change of the motor current does not exceed the predetermined threshold value (step 114), the pulse routine is called (step 116). If the rate of change of motor current is not positive, the control branch simply returns to step 102.

The pulse mode routine is implemented by a variety of different microprocessor-implemented procedures. One such procedure is described in the procedure list given in the "Appendix". Referring to the procedure list, this procedure defines current on-time and current off-time. These are used to generate the motor current waveform shown in FIG. If desired, the on-time and off-time durations can be equal (50% duty cycle) or have different durations. In some embodiments, the on-time duration and the off-time duration are AC.
It can be calculated from the power supply frequency. Alternatively, the on-time duration and the off-time duration can be generated by a clock mounted on the microcontroller 30. By appropriately selecting the on-time value and the off-time value, the frequency of the pulse current signal can be determined at the time of designing the device.

Although the present invention may be implemented in combination with various on-time and off-time, in some tool applications, the on-time and off-time are matched so that the on-time and off-time match the natural resonant frequency of the gear train of the tool. It may be advantageous to choose the time. Generally, there is some play in the gear train of a power tool that allows the motor spindle to rotate between a biased position and a relaxed position when power is applied and cut off, respectively.
Like many physical devices, the motor and its gear train
It has a natural resonance frequency, that is, the frequency at which the oscillation between the biased and relaxed states occurs most naturally. The vibrational energy is increased when a pulsed current synchronized with this natural frequency is applied. To illustrate the principle, consider how to add energy to or near the apex of each bounce in synchronization with the bounce frequency when hand-driving a basketball. Energy is applied at the appropriate times so that the vibrations (bounds) are increased. In exactly this manner, energy is applied to the vibrating gear train.

The natural resonance frequency of the gear train of an electric power tool is
It is determined experimentally using the procedure described in the Appendix procedure. To find the natural resonance frequency, the microcomputer is programmed to iteratively select different on-time and off-time ranges while the torque output of the tool is measured. These on-time and off-time values that correspond to the maximum torque output correspond to the natural resonance frequency of the gear train (or its harmonic frequency in some cases).

Referring to the pseudo code listing in the Appendix, this procedure also defines the pulse mode duration. FIG.
As shown in, the pulse mode duration is the predetermined time the pulse mode routine runs when called. The preferred embodiment of the present invention terminates the pulse mode routine under certain conditions after the pulse mode duration has elapsed. Therefore, when the immobile state is not removed within the predetermined pulse mode duration, the power supply is cut off to prevent the motor from burning.

The procedure of the pseudo code "Appendix" defines the limiting current (current threshold) at which the pulse mode routine ends because the immobility state is cleared.

The procedure begins by initializing the above values. Then the pulse mode duration counter is started. The rest of the routine is executed while the pulse mode duration counter has not elapsed.

The motor current is turned on at intervals defined by the current on time. This is accomplished by starting the current on-time counter and then turning on the motor current before the on-time counter has elapsed. The current sensing device measures the average motor current while the motor current is flowing (on). Preferably, the measurements are made periodically using the circuit described above. When the average motor current is smaller than the initially set limit current, the motor pulse routine is quickly exited. If the operator opens the switch before the current on-time elapses, the motor pulse routine is exited.

After the on-time has elapsed, the off-time is measured. The motor current is turned off and the off time counter is started. Until the off-time elapses, the routine monitors to see if the operator has opened the switch. If the operator opens the switch, the motor pulse routine is exited. After the motor off time has elapsed, the control branch returns to the on time segment of the procedure, which causes the cycle to repeat until the pulse mode duration has elapsed.

When the pulse mode duration counter has reached a state that is reached only if the immobile state is not cleared, the motor is powered off, the brake is applied if desired, and the operator is physically reset. The trigger switch is locked until you do.

Referring to FIG. 5, there is shown a second preferred embodiment of the motor control routine of the present invention. Starting from start step 130, the routine first measures trigger displacement in step 132,
Determines the current setting of trigger switch 24.
Next, in step 134, the average motor current is measured and the motor voltage proportional to the amount of trigger displacement is set (step 136). In this way, the motor is set to run at the speed defined by the trigger setting.

In the embodiment of FIG. 5, the pulse mode operation is performed only when the change in the trigger displacement amount, that is, the change amount is larger than the predetermined threshold value. Therefore, in step 138, the change in trigger displacement is compared to the delta (Δ) trigger threshold. If the change in trigger displacement does not exceed the threshold, control simply returns to step 132. Otherwise, control proceeds to step 140, where the absolute current is compared to the absolute current threshold. If the absolute current is greater than the threshold, pulse mode operation is initiated (step 142). Otherwise, control is step 1
Proceeding to 44, the rate of change of average current over time is analyzed. If the change in average current (di / dt) is greater than the larger threshold value, or if the change in average current is greater than the intermediate threshold value of two consecutive cycles, pulse mode operation is initiated (step 142). If none of these tests in step 144 are satisfied, then
Control returns to step 132.

The motor will continue to operate in pulse mode unless something happens. If the average current is greater than the upper threshold during pulse mode operation, as shown in steps 146 and 148, the motor is de-energized. Also,
If the average current is less than the smaller threshold, as shown in step 150, pulse mode operation ends and control returns to step 132.

Continuing with the description, FIG. 6 is a graph showing the motor current of the electric drill incorporating the present invention. Motor torque is proportional to motor current, so the graph of FIG. 6 also shows how to control motor torque. When the tool is switched on, the motor current increases rapidly, as indicated by A, and the tool is accelerated to full speed. After that, the motor current decreases to the normal operating current as shown by B. While the work is being drilled, the motor current fluctuates slightly up and down due to changes in work hardness and changes in pressure applied by the operator. Apart from these small variations, the motor current is essentially constant while the drill bit is cutting the workpiece, as shown in inset I of FIG.

When penetration occurs as shown in inset II,
The motor current increases rapidly as indicated by C. More specifically, the rate of change of the motor current is faster than the rate of change during the initial acceleration indicated by A. The reason for this rapid increase in motor current is that the holes on the outlet side of the work piece are not yet perfectly round and there are burrs or non-removed parts of material, which penetrate into the groove parts of the drill bit.

When a rapid increase in motor current is detected in accordance with the present invention, the pulse mode routine is called and the motor current is pulsed as indicated by D. It should be noted that the peak motor current (and motor torque) achieved during this pulse mode operation is substantially greater than the average motor current (and average torque) during this period.
The peak motor current and peak torque are substantially greater than the average torque during normal drilling indicated by B. Also,
The peak current reaches a maximum value at E, and then decreases so that each peak becomes continuous. Finally, the peak current is
The current threshold is reduced to F, after which normal (non-pulsed) operation is resumed.

During each pulse of pulse mode operation, the cutting edge of the drill bit is driven to impinge on the work material that is not burred or removed in a sculpting manner. After each impact, the gear train can relax, allowing the cutting edge of the drill bit to retract slightly for the next impact. In this way, the cutting edge of the drill bit performs a chopping motion and the peak torque produced during each chop is substantially greater than the average torque (the torque that the motor can generate without the chopping motion). This pulsing action allows the tool to overcome any residual burrs or other material obstacles. After the penetration of the work piece has occurred, the tool resumes normal operation, which causes the hole to move, as shown in inset III.
You can wear it more beautifully. Pulsing also informs the operator that the above condition has occurred.

It should be noted that during this full pulse mode operation, the trigger switch remains in the actuated state by the tool operator. If a rapid increase in motor current is required, the device will automatically enter pulse mode operation and the operator can concentrate on the drilling or cutting operation and simply keep the trigger switch closed. Good.

If the pulse mode operation is unsuccessful in overcoming the immobile state, the power supply to the motor is cut off after the lapse of a predetermined pulse mode duration.

Although a drill bit is shown in insets I-III of FIG. 6, the present invention is also useful with other types of power tools, as described above. In the case of electric saws, a potential immobility occurs after the cutting is complete, causing some of the removed material to become jammed between the saw teeth and the rip fence or other guide. The pulsing action of pulse mode operation frequently vibrates the workpiece to clear the jam and inform the operator of this condition. Thus, the present invention can be incorporated into a wide range of power tools, including drills and saws.

For a better understanding of the motor control routine of FIG. 5, please refer to FIGS. 7, 8 and 9. These figures show the average motor current (A of microcontroller 30 as a function of time (time measured in line cycles).
The A / D value generated by the / D conversion circuit is shown.

The preferred embodiment of FIG. 5 implements pulse mode operation which is synchronous with the AC line frequency. The pseudo-code listing in the "Appendix" shows a more generalized case where pulse mode operation is not necessarily synchronized to line frequency. In the pseudo code listing, the on-time and off-time can be any value measured by the microprocessor clock circuit. In the embodiments shown in FIGS. 7-9, the on-time and off-time are measured by counting a predetermined number of AC line cycles instead of the clock circuit of the microprocessor. A
For C power tools, the embodiment of Figures 7-9 is preferred. For DC power tools, such as cordless battery power tools, the clock-based implementation of the microprocessor can be used.

FIG. 7 shows a first example of the operation of the device of FIG. After the switch is turned on, as shown by A,
The average motor current drops to the stable operating value indicated by B.
This current is indicative of normal tool operation without tension immobility. At C, the current increases rapidly, indicating a state of immobility. As described with reference to FIG. 5, the immobility state occurs when the following two conditions are satisfied. Condition 1: The increase in average motor current as a function of time is greater than a predetermined delta threshold. FIG. 7 shows this delta threshold as a first derivative or slope corresponding to the rate of change or predetermined rate of current increase. Condition 2: The average motor current exceeds the absolute threshold. FIG. 7 shows the absolute threshold as any current greater than the smaller threshold shown. Once one of these two conditions (in this case,
When the first condition) is met, pulse mode operation is started. If the cause of the immobility state is not eliminated after a predetermined time (after a predetermined number of line cycles), the motor current is cut off, as indicated by point G. In this case, since the average current peak exceeds the larger threshold value, the motor current is interrupted.

FIG. 8 shows a case where the motor current enters the pulse mode operation at point C and then returns to normal operation at point F.
Normal operation resumes because the motor current drops below the smaller threshold.

FIG. 9 shows the case where the pulse mode operation starts at point C and continues this mode without stopping the motor. The peak motor current during pulse mode operation drops below the larger current threshold. Since the larger threshold is not reached, pulse mode operation continues. FIG.
Note that in FIG. 7, the average current peak exceeds the larger threshold during pulse mode operation. Therefore, in FIG. 7, the pulse mode operation ends and the motor current is cut off at point G, whereas in FIG. 9, the pulse mode does not end.

FIG. 10 illustrates how the present invention may be used in an AC power drill. The component group in the embodiment of FIG. 10 is shown in FIG.
Corresponds to the block diagram of. Therefore, please refer to FIG. 2 which outlines the functions of these circuit components. Referring to FIG. 10, the preferred power supply circuit 32 of the present invention uses a Zener diode to provide a low voltage power supply voltage to the various components of the circuit and comprises a 5V DC power supply and a 12V DC power supply.

The circuit of FIG. 10 has the illustrated pinout (pin-
out) and is configured using the ST6210A microcontroller circuit connected according to the above. The resonator 200 is
Maintain proper clock frequency for the microcontroller. The trigger switch circuit 24 is connected to the A / D input pin 10 of the microcontroller 30. Therefore,
The microcontroller 30 can monitor the setting of the trigger switch. AC line frequency sense resistor 20 connected to high impedance input pin 8
2 to the microcontroller 30. This provides a signal to the microcontroller 30 that synchronizes and generates the time base that controls the rate of pulse mode operation, from which the AC line frequency is derived.

Under certain conditions, the microcontroller 30
Shuts off the power supply to the LEDs intended for optical display. Microcontroller 30 provides a signal to pin 12 which is connected to the base of transistor 204 for this purpose. To enable the microcontroller 30 to monitor the state of the triac drive circuit 36,
Pin 15 is connected to the 5V power supply via pull-up resistor 206. Pin 15 is also connected to the trigger terminal of triac 36 via resistor 208. Based on the state of the triac, pin 15 of the microcontroller 30 is pulled down, which outputs a signal of the state change of the triac drive circuit.

Microcontroller 30 controls the operation of triac drive circuit 36 via pin 19. Pin 19 is the transistor 212 of the triac drive circuit.
Connected to the base. This transistor 212 is supplied with a variable duty cycle alternating signal which activates a triac. The triac is preferably connected to the neutral side of the motor circuit as shown.

When the motor operates, the motor current flows through the current detection register 38. The current detection register is
It can be constructed with a high wattage low resistance (0.01 ohm) device. The voltage drop across resistor 38 is measured by average current monitoring circuit 40. The output of the circuit 40 is provided to the A / D input pin 11 of the microcontroller 30. This signal is used to determine when to enter (or exit) pulse mode operation and when to shut off power to the motor.

The preferred average current monitoring circuit 40 of the present invention provides cycle-by-cycle average current measurements. The operational amplifier 214 reflects the voltage drop measured across the current detection register 38. This reflected voltage is applied to the base of transistor 216, which draws current through capacitor 218 to maintain the voltage established by transistor 216 and the value of resistor 220. The motor current i _{ave for} each cycle can be calculated from the voltage V _{c of the} capacitor 218 using the following equation. Here, R _s is the resistance of the register 38 and R _i is the register 220.
And T is the duration of the AC line current (eg 1
0 msec).

The voltage V _{c of the} capacitor 218 is supplied to the A / D input pin 11 via the register 221. Once the A / D conversion by the microcontroller is complete, pin 11 discharges capacitor 218 through resistor 221 to accept the next positive 1/2 cycle of current for the purpose of resetting the cycle-by-cycle average current circuit. Set to high output state. Resetting the circuit allows the device to measure the average current of the motor with a strict line cycle response time to accurately and instantaneously detect a rapid increase in motor current.

[0053]

From the foregoing, it will be appreciated that the present invention provides a motor control circuit and method that can be incorporated into a wide variety of power tools for detecting (and in some cases overcoming) an immobility condition. . The power tool to which the present invention has been introduced is easier and more convenient to operate because the operator can concentrate on accurate drilling or cutting without suffering from immobile states such as penetration, seizure, and kickback. Another advantage is that when an immobility condition occurs, the pulsing effect of the present invention provides a torque burst that overcomes the immobility condition, but the operator does not feel it because the average torque is kept small. That is. However, the pulsing action serves to inform the operator that a potential immobility condition exists. The power tool to which the present invention is applied has almost no tendency to twist the hand of the operator.

Although the present invention has been described in terms of its preferred embodiment, it will be understood that the invention can be modified without departing from the spirit of the invention as set forth in the following claims. For example, although the present invention was primarily described for application to AC power drills, it is equally applicable to battery powered tools.

APPENDIX Pulse mode routine Initial setting of current on-time. Initial setting of current off time. Initial setting of pulse mode duration. Initial setting of limiting current (current threshold). Start of pulse mode duration counter. Starts [Pulse motor: ON when ON time] before the pulse mode duration time has elapsed. Starting the current on-time counter. Current turn-on before current on-time elapses. Measurement of average motor current. If the average motor current is less than the limit current, exit the motor pulse routine [exit early if immobile state is removed]. Otherwise, exit the motor pulse routine if the switch is open [Escape early if switch is open]. Otherwise, End While [Pulse Motor at Off Time: Off] Turn off current. Starting the current off-time counter. If the switch is open before the current off-time counter has elapsed, exit the motor pulse routine (exit early if switch opens). End while [Repeat the above items until the pulse mode duration elapses]. Cut off power to the motor. Lock out trigger switch (until physically reset). Finished.

[Brief description of drawings]

FIG. 1 is a side view showing a general variable speed electric drill using a control circuit of the present invention.

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

FIG. 3 is a flowchart showing an embodiment of the present invention.

FIG. 4 is a pulse mode timing diagram useful in understanding the present invention.

FIG. 5 is a flow chart showing another preferred embodiment of the present invention.

FIG. 6 is a graph showing motor current as a function of time for how the motor is controlled during normal operation and during pulse mode operation.

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

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

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

FIG. 10 is a detailed schematic diagram of a motor control circuit of an electric drill incorporating the present invention.

[Explanation of symbols]

 10 Electric Drill 12 Control Circuit 16 Motor 20 Gear Train 24 Trigger Switch 28 Groove Shank 30 Microcontroller 32 Power Supply Circuit 36 TRIAC Drive Circuit 38 Current Sensor 40 Average Current Measurement Circuit 42 Current Detection Circuit

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Paul Giffever, Mayner Road, Phoenix, 21131, Maryland, USA 14710 (72) Inventor Fargan Patel, Maryland 21009, Abingdon, Cheverley Court, 3337

Claims (10)

[Claims] 1. A method of controlling an electric tool having a motor that transmits torque to an output spindle when actuated by a switch operable by a worker, wherein a motor parameter is detected and the initiation of a tension immobility state is indicated. Detecting a rapid change in the value of the parameter and pulsing the motor multiple times while the switch is in the actuated state to provide a continuous torque pulse, the continuous torque pulse being an average given during this continuous torque pulse. A control method having a peak torque substantially larger than the torque. 2. The control method according to claim 1, wherein the detected motor parameter is a motor current, and the detecting step detects a rapid increase in the motor current. 3. The control method according to claim 1, wherein the motor is driven by an alternating current having a predetermined cycle frequency, and the motor parameter detecting step is repeatedly performed in synchronization with the cycle frequency. 4. The motor is driven by an alternating current having a predetermined cycle frequency, and the pulsing step is performed by blocking a current flow to the motor in synchronization with the cycle frequency. Item 2. The control method according to Item 1. 5. The tool of claim 1, wherein the tool has a characteristic natural resonant frequency and the pulsing step is performed at a frequency substantially harmonically related to the natural resonant frequency. Control method. 6. A drive circuit (36) connected to a motor (16), the drive circuit (36) controlling the supply of current to the motor, and the drive circuit (36) connected to the drive circuit (36). Drive circuit (36)
A processor (30) for providing a processor output signal for controlling the motor, and a processor (30) connected to the drive circuit (36) for detecting a parameter indicative of a motor current and a first processor input signal for supplying a first processor input signal. Means (108) for detecting a rapid change in the value of the first processor input signal to detect the onset of an immobile state. -114), the processor (30) further comprising: means (14) for using the processor input signal to supply a current pulse to the motor in response to a detected start of immobility.
2) A motor control circuit for an electric power tool (30), which comprises: 7. A second means for providing a current supply to a motor.
An operator operable switch (2) connected to the processor (30) for providing a processor input signal.
4), wherein the second means (142) comprises the second
7. The motor control circuit according to claim 6, wherein the processor input signal is periodically invalidated and the current supplied to the motor is cut off. 8. The motor (16) is driven by alternating current and the current sensor (38, 40) detects the average motor current at least once per cycle of the alternating current. The motor control circuit described in. 9. Means (146,148) for the processor (30) to further terminate the supply of current pulses to the motor after a predetermined time or in response to detecting that the immobile state has been cleared. The motor control circuit according to claim 6, further comprising: 10. The power tool (10) has a characteristic natural resonance frequency, and the second means (142) of the processor applies to the motor at a frequency substantially harmonically related to the natural resonance frequency. The control circuit according to claim 6, wherein the control circuit supplies a current pulse.