JPH04172992A - Controlling circuit for dc motor - Google Patents

Abstract

PURPOSE:To eliminate a clutch mechanism for limiting a torque by so limiting the torque of a DC motor as to stop the rotation of the motor when the torque of the motor reaches an upper limit torque. CONSTITUTION:A torque comparator AP1 always compares present torque detection output with an upper limit torque set output from a torque limit setter TL. When a screw is clamped so that the rotating speed of a DC motor M is lowered while present torque is increased to reach the upper limit torque of the motor M, the output unit of the comparator AP1 outputs a rotation stop output for stopping the rotation of the motor M. Since a switch C1-E1 is closed in response to the input of this DC motor stopping output, a bypass transistor TR1 is bypassed by a bypass passage BP1 at the oscillation pulse output from an oscillator OC. As a result, a switching element TR4 is turned OFF, and the motor M is stopped to be rotated.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a DC motor control circuit for controlling the rotation of power tools and other power tools driven by a DC motor, such as electric tribars, electric trills, electric saws, etc. Regarding.

(Prior art) Conventionally, as a DC motor control circuit for the above-mentioned power tool,
The one shown in FIG. 3 has been proposed.

This connects the switch part (train-source) Ds of the switching element TR composed of FETs between the power supply E and the DC motor M, and applies an oscillation pulse from the oscillation circuit OC to the gate of the switching element TR. By applying an output and turning off the switch section D-S, when the switch section D-9 is on, the power source E is applied to the DC motor ~1.

On the other hand, a voltage setting circuit VRI and an oscillation circuit OC are connected in parallel to a constant voltage circuit consisting of a resistor R and a Zener diode ZD, and a voltage setting circuit VRI is constructed of a variable resistor.
By interlocking the movable terminal T with the operating lever of the power tool, a set voltage proportional to the operating stroke (pulling amount of the operating lever) of the operating lever from the free position is generated from the voltage setting circuit VRI, The oscillation circuit OC modulates and outputs the pulse width of an oscillation pulse in response to the magnitude of the manually input set voltage, that is, the operating stroke of the operating lever.

Therefore, the switching element TR is turned on and off in accordance with the operation stroke, and accordingly, the rotation speed of the DC motor M is controlled.

In such a DC motor control circuit, the torque and rotational speed of the DC motor M are as shown in FIG.

Fig. 4 shows the torque on the horizontal axis and the rotational speed on the vertical axis regarding the DC motor M, and also shows the switching element TR.
The torque and rotational speed of the DC motor M when the ratio of the on period to the total period (on duty) is 40% to 100%. The relationship is shown here.

That is, as is clear from FIG. 4, when the conventional DC motor control circuit is applied to, for example, an electric screwdriver and the electric screwdriver is used to tighten a screw, the operation stroke of the operation lever is constant; Based on the degree of modulation of the oscillation pulse from the oscillation circuit OC, which is determined by As the torque increases, the rotational speed will decrease along the 50% on-duty characteristic line.

(Problem to be Solved by the Invention) As described above, in the conventional DC motor control circuit, as the screw is tightened to a certain degree, the rotation speed decreases. As a result, if the torque becomes excessive, the screw may be damaged by the excessive torque.

However, conventional DC motor control circuits themselves do not have a torque limit function, and in order to avoid this kind of screw damage, some power tools have been equipped with torque limit mechanisms. but,
This torque limit mechanism was a clutch mechanism that mechanically limited the torque by slipping the rotation of the DC motor M, so when the torque limit was activated, a loud slip noise that caused discomfort to the operator was generated. Or, because the torque limit operation was done in stages, it was difficult to increase the accuracy of the torque limit setting.
Since components that require mechanical strength are required, the mounting components become heavier, which results in the power tool itself becoming heavier and reducing operability. In addition to being expensive, the installation space for the clutch mechanism hindered the design freedom of the power tool itself, which caused various problems.

Therefore, in view of the above-mentioned problems, the present invention makes it possible to limit the torque of a DC motor without using a clutch mechanism, thereby solving the above-mentioned problems caused by using a clutch mechanism. The purpose is to

(Means for Solving the Problem) In order to achieve such an object, the DC motor control circuit of the present invention includes a switching element, a torque detection circuit, a torque limit setting circuit, and a torque comparison circuit. In the switching element, the switch part is connected between the power supply and the DC motor, and the switch part is turned on and off by an oscillation pulse output, and the torque detection circuit is configured to detect the torque flowing through the switch part of the switching element. The current torque of the DC motor is detected and output from the current, the torque limit setting circuit is used to set and output the upper limit value (upper limit torque) of the torque of the DC motor, and the torque comparison circuit is used to detect and output the current torque of the DC motor. The current torque from each limit setting circuit is compared with the upper limit torque, and when the current torque reaches the upper limit torque of the DC motor, a DC motor stop output is output from the output section to stop the DC motor. It is said that

(Function) In the torque detection circuit, the current torque of the DC motor is detected and output. In the torque comparison circuit, the current torque detection output is compared with the upper limit torque setting output from the torque limit setting circuit, and when the current torque reaches the upper limit torque of the DC motor, the DC motor stop output is output from the output section. This causes the DC motor to stop rotating.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings. In this embodiment, the present invention will be explained by applying it to an electric screwdriver as an example of a power tool, but it goes without saying that it can be applied to other power tools as well as other driven objects.

FIG. 1 is a circuit diagram of a DC motor control circuit according to an embodiment of the present invention. The DC motor control circuit according to the ninth embodiment shown in the figure includes a constant voltage circuit consisting of a resistor R1 and a Zener diode ZD, and a switching element TR, as in the conventional case.
4. It has a voltage setting circuit VR1 and an oscillation circuit OC.

In addition to the above configuration, the control circuit of this embodiment includes a torque detection circuit TD, a torque limit setting circuit TL, a torque comparison circuit API, a bypass transistor TRI, and a self-holding circuit SH.

The configuration of this embodiment will be explained in more detail below.The switching element TR4 is composed of an FET as in the conventional case, and the switch part D-5 is connected between the power supply E and the DC motor M, and in detail, the drain D is at one end of DC motor M,
A source S is connected to a negative electrode of a DC power source E, respectively. The voltage setting circuit VRI is composed of a variable resistor connected in parallel to a Zener diode ZD,
As in the past, the movable terminal T is interlocked with an operating lever (not shown) of the power tool, thereby generating a set voltage Vs proportional to the operating stroke of the operating lever from the free position via the movable terminal T. It looks like this.

The oscillation circuit OC outputs an oscillation pulse of a constant frequency, the pulse width of the oscillation pulse is modulated according to the set voltage Vs, and the oscillation pulse is output through a current limiting resistor R4. The signal is output to the gate of the switching element TR4. The torque detection circuit TD includes a current detection resistor R that detects the current flowing from the DC motor M through the switch section D-8 of the switching element TR4.
1O, a smoothing circuit consisting of a resistor RIO and a capacitor C, and the switch part D of the switching element TR4
-The current flowing through S is detected by the current detection resistor R11, and the detected output is smoothed by a smoothing circuit and used as the current torque output of the DC motor M, and the torque comparison circuit AP
It is designed to be output to the non-inverting input part (+) of I.

The torque limit setting circuit TL is composed of a variable resistor VR2, resistors R8, and R9, and the variable resistor VR2 can set the upper limit value (upper limit torque) of the torque of the DC motor M. The value can be outputted to the inverting input section (-) of the torque comparison circuit API as the upper limit torque output. The torque comparison circuit API compares the current torque and the upper limit torque output from each of the torque detection circuit TD and the torque limit setting circuit TL, and when the current torque reaches the upper limit torque of the DC motor M, the output part outputs the DC motor. It is designed to output a stop output.

The bypass transistor TR1 is connected to the base or the output part of the torque comparator circuit API, and the switch part (collector-emitter, hereinafter the same) CI-El is inserted into the bypass passage BP circuit for the oscillation pulse output. In addition, in response to the human power of the DC motor stop output, the switch section CI-El is turned on to bypass the oscillation pulse output.

The self-holding circuit SH includes an operation stroke detection circuit O8,
First and second self-holding transistors TR2, TR
3. The operation stroke detection circuit OS is composed of resistors R2, Rs, R5, and a comparator circuit AP2. The comparator circuit AP2 outputs the reference voltage Vr e f with respect to the voltage setting circuit VRI.
This is to compare the set voltage Vs applied to the inverting input part (-) from the reference voltage Vr e f applied to the non-inverting input part (1) as described above, and both voltages Vs and Vre Based on f, the operating lever compares and outputs a high-level self-holding output that enables the first self-holding transistor TR2 to be turned on in response to the operating stroke when the operating lever is not in the free-standing position, and At this time, a low-level self-holding release output that turns off the first self-holding transistor TR2 is compared and output. First self-holding transistor TR2
, the switch section C2-E2 is inserted into the bypass passage BP2 for the DC motor stop output from the torque comparison circuit API, and the operation stroke detection circuit O8
When the switch section CI-El of the bypass transistor TRI is turned on by the DC motor stop output while a self-holding output is being given from the switch section C2-
E2 is supposed to be turned on. In the second self-holding transistor TR3, the switch portion C3-E3 is inserted into the bypass path BPB for the upper limit torque setting output from the torque limit setting circuit TL, and the first self-holding transistor TR2 switch part CI
-E When I is on, the relevant switch C3-
E3 is turned on to bypass the torque limit setting output.

The operation will be explained with reference to FIG. In Figure 2, the horizontal axis represents the torque of the DC motor M, and the vertical axis represents the rotation speed of the DC motor M, and the on-duty is 60% and 50%, respectively.
, 40%, the DC motor M according to the control circuit of this embodiment
shows the relationship between torque and rotation speed.

Then, when the screw is tightened and the DC motor M is being strongly rotated with the voltage setting circuit VRI at 50% on-duty, for example, the current torque of the DC motor M is detected and outputted by the torque detection circuit TD. has been done. In this state, in the torque comparison circuit API, the current torque detection output is always compared with the upper limit torque setting output from the torque limit setting circuit TL, and the output is set to zero.

In this comparison, when the screw is tightened and the rotational speed of the DC motor M decreases, while the current torque increases and reaches the upper limit torque of the DC motor M, the output part of the torque comparison circuit API A rotation stop output force is output to stop the rotation of the DC motor M. Then,
) The output transistor TRI inputs this DC motor stop output (in response to this, the switch C1-El is turned on, and the oscillation pulse output from the oscillation circuit OC is As a result of being bypassed to the path BPI, the switching element TR4 is turned off and the DC motor M is stopped from rotating.

On the other hand, when the operation stroke detection circuit O5 in the self-holding circuit SH is outputting a high-level self-holding output that enables the first self-holding transistor TR2 to turn on, the first self-holding transistor TR2 is turned on. , its switch section C2-E2 is a bypass transistor T
Turns on when there is a DC motor stop output to switch section CI-E1 of RI. As a result, the switch section C3-E3 of the second self-holding transistor TR3 is turned on, so that the torque limit setting output is bypassed via the bypass path BP3.

In this way, when the second self-holding transistor TR3 is turned on, the torque comparator circuits A and PI always output the DC motor rotation stop output, and thereby the bypass transistor TRI outputs the oscillation circuit OC output. Since it is bypassed, no matter what current torque detection output is given to the torque comparison circuit API from the torque detection circuit TD, the DC motor M will stop rotating when the torque reaches the upper limit value.

As a result, the torque of the DC motor M changes from the solid line to the broken line in FIG. 2, and the DC motor M does not rotate beyond the upper limit torque.

In this case, when the operation lever is set to free position, the operation stroke detection circuit O8 outputs a self-holding release output of the lower line, thereby turning off the first self-holding transistor TR2 and turning off the second self-holding transistor TR2. As a result of the self-holding transistor TR3 also being turned off, the DC motor is released from its rotational stop state and can be rotated again in response to the operating stroke of the operating lever.

(Effects of the Invention) As is clear from the above explanation, according to the present invention,
When the torque of the DC motor reaches the upper limit torque, the torque can be limited so as to stop the rotation of the DC motor, which eliminates the need for a conventional clutch mechanism to limit the torque. You can solve all the problems at once.

In addition, in conventional devices that limit the torque and control the constant torque, the DC motor stops rotating in a locked state and does not perform any work, causing unnecessary power loss.However, in the present invention, the torque is When the limit torque is reached, the rotation of the DC motor is stopped, so the current flowing to the DC motor is actually reduced, resulting in no unnecessary power loss.

[Brief explanation of drawings]

1 and 2 are related to the present invention, FIG. 1 is a circuit diagram of a DC motor control circuit according to an embodiment of the present invention, and FIG. 2 is a rotation speed and torque of a DC motor according to the control circuit of FIG. 1. FIG. 3 and 4 relate to the conventional example, FIG. 3 is a circuit diagram of a DC motor control circuit according to the conventional example, and FIG. 4 is the relationship between the rotation speed and torque of the DC motor according to the control circuit of FIG. 3. FIG. TR4...Switching element, VRI, voltage setting circuit, OC oscillation circuit, TD, torque detection circuit, TL...
Torque limit setting circuit, A, PI Torque comparison circuit, TR+ ... Bypass transistor, SH/self-holding circuit, O8 operation) O-reduction detection circuit, TR2, T
R3: Self-holding transistor. Figure 2 Figure 3 Figure 4 Torque

Claims (1)

[Claims] (1) Switching element (TR4), torque detection circuit (
TD), a torque limit setting circuit (TL), and a torque comparison circuit (AP1), and the switching element (TR4) has a switch part (D-S) that connects the power supply (E) and the DC motor (M). The torque detection circuit (TD) is connected to the switching element (TR4
) is used to detect and output the current torque of the DC motor (M) from the current flowing through the switch section (D-S) of the DC motor (M).
The torque comparison circuit (AP1) sets and outputs the upper limit value of the torque (upper limit torque) of the torque detection circuit (TD).
The current torque from the and torque limit setting circuit (TL) is compared with the upper limit torque, and the current torque is determined from the DC motor (
A DC motor control circuit characterized in that when the upper limit torque of M) is reached, a DC motor stop output is output from an output section to stop the DC motor (M).