JPS63302793A - Torque limiter for motor - Google Patents

Abstract

PURPOSE:To expedite the response, by detecting the size of the current value by means of a comparator. CONSTITUTION:When the current of a DC motor 2 becomes more than a specified value, the output of a current detection circuit 3 becomes H level, and a capacitor is charged through a charging integration circuit section 5. When the potential of the capacitor becomes higher than the value of the reference voltage Vref, the output of a comparator 7 becomes L level and a switching circuit 9 is turned OFF, stopping the power supply to the DC motor 2. When no current is supplied, the output of the current detection circuit 3 becomes L level and the capacitor is thereby discharged through a discharging integration circuit section 6. In starting the DC motor 2, a starting current trap circuit 11 is activated.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a motor torque limiter that is connected in series with a motor and arbitrarily sets upper and lower limits of the motor's torque to prevent overload. .

In other words, it limits the current supplied to the motor in excess of a set value.This type of limiter is effective in preventing the motor from burning out when an overload is applied to the power windows and wipers of automobiles. It is.

(Prior art) For controlling the motor torque below a set value,
A Ti flow limiter using a thermal relay is known. This converts current into heat and uses bimetals to interrupt the circuit.

(Problems to be Solved by the Invention) ``Such thermal relays have the disadvantage of slow response and are inconvenient in use because they must be reset after being cut off.

SUMMARY OF THE INVENTION An object of the present invention is to provide a torque limiter for a motor that does not require reset and has a quick response.

(Means for Solving the Problems) The torque limiter of the present invention is provided with two terminals so as to be connected in series between the motor and the power source, and is capable of arbitrarily setting the upper and lower limits of the torque control range. It detects the current and compares it with the upper limit value, and when the current exceeds this upper limit value, it switches to maintain the effective torque at the lower limit value by pulse width modulation. Instantaneous large current at the initial stage (vJ current)
This is characterized in that the motor is allowed to be energized by a VJTi current trap circuit.

Here, "pulse width modulation" broadly refers to duty ratio control that controls the ratio of pulse on and off times, and refers to so-called chopping control.
It broadly includes not only PWM111 control but also PPM control and the like.

Further, the above-mentioned motor does not matter whether it is a direct current or an alternating current motor.

Preferably, the torque limiter of the present invention is provided with a rectifier that causes a current to flow in a fixed direction to the current detection circuit, regardless of the direction of the armature current flowing to the motor, in the input stage connected to the two terminals. , for alternating current, normal! ! 8! In the case of direct current, the torque limiter is made to function as a non-polar type so that there is no need to check the polarity when connecting the torque limiter.

(Effects of the Invention) According to the torque limiter of the present invention, the magnitude of the current value is detected using a comparator instead of using a thermal relay, so the response is quick and the effective torque can be kept below the 0 level. By setting the lower limit value to a slightly larger value, resetting can be made unnecessary, which is a great advantage in use. Furthermore, since the effective torque is lowered by pulse width modulation, less heat is generated and stable control can be performed.

Furthermore, since the circuit can be configured using only inexpensive electronic components without using expensive components (bimetals) such as thermal relays, manufacturing costs are reduced.

(Example) Hereinafter, an example of the present invention will be described in detail using the drawings.

FIG. 1 is a block diagram conceptually showing a motor torque limiter according to a first embodiment. This @ place is straight 8! A current detection circuit 3 detects the output current from the DC motor 2 driven by the power source 1; an amplification section 4 amplifies the output current from the Ti current detection circuit 3; A charge integration circuit unit 5 is arranged in parallel with the charge integration circuit unit 5 to integrate the voltage with a time constant and output a voltage according to the integrated value. When the charge reaches a predetermined value, this mA is discharged at a predetermined time constant, and a discharge integration circuit section 6 outputs a voltage corresponding to the value of the residual charge; any one of the integration circuit sections 5.
A comparator 7 that compares the output voltage from 6 with a reference voltage (■*ef) and outputs a signal according to the comparison result, a first setting unit 8 that sets this reference voltage to a predetermined value, and this comparator It consists of a switching circuit 9 that performs ON-OFF switching operation of the drive current to the DC motor 2 based on the output signal from the DC motor 7.

Here, the two integrating circuit sections 5 and 6 are provided with second setting sections 10a and 10b which are time constant adjustment mechanisms.

By adjusting the second setting sections 10a and 10b, the pulse period and pulse width of the control pulse output from the comparator 7 can be set to desired values, and this control pulse is input to the switching circuit 9 to control the motor. Drive current PWM (Pulse Width Modulat)
ion ) control, the lower limit value of the effective torque of the motor can be maintained at a desired value.

In addition, in order to prevent the device from operating depending on the starting current of the motor, the device absorbs this generated vJ current. #l
A current trap circuit 11 is provided. The connection position of this trap circuit 11 is not limited to the position shown in FIG. 1, but may be connected to any position as long as it can reliably trap the starting current. It may be between 7 and 7.

Next, the specific circuit configuration and operation of the @ location of this embodiment will be explained with reference to FIG. When the DC motor 2a is driven by the first power source 1a, the driving current of the DC motor 2a flows in the six directions of the arrows and is input to the diode bridge 13 from the first terminal 2a.

On the other hand, when the DC motor 2a is driven by the second power supply 1b having the opposite polarity to the first power supply 1a, the above-mentioned drive! l
I current flows from the second terminal 12b to the diode bridge 13
is input. However, in any case, the rectifying function of the diode bridge 13 makes it possible to obtain a current in a fixed direction (direction of arrow C). Thereafter, when the Darlington-connected power transistor 14 is in the ON state, the current output from the diode bridge 13 flows through this transistor 14 and the resistor R1 to the diode bridge 13 as W1''11, and further flows to the input terminal. It is output from the opposite terminal and fed back to the DC motor 2a, thereby causing the DC motor 2a to rotate steadily.

By the way, when the DC motor 2a is rotating in a steady state, the point P1 is set to a constant low potential by the resistor R1. However, when the DC motor 2a becomes overloaded, the current flowing through the resistor R1 increases, so the potential at point P1 rises, and when this potential exceeds a certain value, the comparator 1
5 is activated to generate a predetermined potential at the output terminal of this comparator 15. That is, the resistor JARt and the comparator 15 function as the current detection circuit 3 in FIG.

When a voltage is generated at the output terminal of the comparator 15, that is, the point P2, the current flowing through the variable resistor R2 and the diode D1 causes the capacitor C1 to
It is charged according to a time constant (CR) determined by

Variable resistor R2 corresponding to the second setting section 10a shown in FIG.
I! is located on the front panel. Adjustable volume (T
RQ) allows the resistance value to be adjusted to rJ1. The variable resistor R2, the diode DI, and the capacitor CI form the charging integration circuit section 5 shown in FIG.

As charge accumulates in the capacitor C1, the potential at point P rises, the input voltage to the negative terminal of the comparator 16 increases, and the value of this input voltage becomes the voltage at the positive terminal of the comparator 16. The output voltage of the comparator 16 becomes 0 level when it becomes larger than the value of the reference voltage (Ref) which is the input voltage to the circuit system. The voltage is divided and taken out, and the voltage value is set by variable resistor R3.
! l is now possible. Adjustment of this variable resistor R3, which corresponds to the first setting section 8 shown in FIG. 1, is performed by adjusting a control volume (CLIR) provided on the front panel. Note that this comparator 16 functions as the comparator 7 shown in FIG.

When the output voltage of the comparator 16 becomes O level, the first transistor 1 of the Darlington connection transistor 14
Current no longer flows to the base of 4a, and this Darlington connection transistor 14 is turned off. As a result, power supply to the overloaded DC motor 2a is stopped. Note that this Darlington connection transistor 14 functions as the switching circuit 19 shown in FIG.

When current is no longer supplied to resistor R1, the potential at point P1 becomes O.
As a result, the output terminal of the comparator 15 becomes O level. In this state, since the potential of P3 is higher than the potential of P2, the charge accumulated in the capacitor CI is transferred to the capacitor 0 and the resistors Ra and R via the diode D2, the resistor R4, and the variable resistor R2.
It is discharged according to a time constant (OR) determined by z.

The portion of the variable resistor R2 used during this discharge is the portion opposite to the center tap portion of the resistor portion used when charging the capacitor C1. Therefore, if the total resistance value of the variable resistor Rz is Rt, and the value of the variable resistor Rz during charging is R'', then the value of the variable resistor Rz during discharging is R'-R''. Note that the discharge integration circuit section 6 shown in FIG. 1 is formed by the capacitor CI, the diode Dzs resistor R4, and the variable resistor R2. Further, the variable resistor Rz at this time corresponds to the second setting section 10b shown in FIG.

When the charge accumulated in the capacitor C1 is discharged and the potential at point P3 decreases, the voltage input to the negative terminal of the comparator 16 decreases, and the reference voltage input to the positive terminal of the comparator 16 ( ■*ef), the comparator 16 generates a predetermined voltage at the output terminal, which causes the Darlington connection transistor
4 is turned on, and drive current is again supplied to the DC motor 2a. By the way, this comparator 16 has a hysteresis function, and the threshold level (LTP) when the voltage input to the negative terminal decreases is the same as the threshold level (UTP) when the voltage input to the negative terminal increases.
P) is set to be lower than P). Therefore, the voltage input to the negative terminal changes from LITP to LTP.
A period in which the drive current is OFF forms a period in which the drive current is OFF, and a period in which the drive current is ON is formed in a period in which this voltage rises from LTP to UTP.

By the way, if the DC motor 2a continues to be in an overload state, the ON/OFF switching of the motor drive current as described above is repeatedly performed. In other words, the motor drive current is
0N-OFF corresponding to the charging and discharging time of capacitor C1
switching is performed, and this causes the motor torque P
WM control is performed. Such PWMMIII allows the motor to be driven with extremely small effective torque by adjusting the ratio of ON and 0FFWAII of the drive current. Therefore, the load on the motor can be reduced and the heat generated by the load can be suppressed. Further, since the drive current circuit is not completely cut off, when the overload condition is released, the steady state can be immediately returned to without using a reset mechanism or the like.

Further, the electrolytic capacitor Ct, the resistor R4, and the transistor 17 function as a starting Ti current trap circuit 2111 to prevent the comparator 16 from operating due to the starting current of the DC motor 2a, and the time constant CR in this case is , is set so as to absorb the startup ff1FE of about 1 second. Generally, the drive current (electromotive vJ current) when starting a motor is extremely large compared to the drive vJ current when the motor is rotating steadily, and if there is no trap circuit 11 like this, the comparator 16 is activated and the wAvJ current is temporarily cut off, so it is necessary to provide such a trap circuit 11.

Furthermore, the Zener diode Dz arranged in parallel with the diode bridge 13 is for absorbing spike noise accompanying switching of the motor drive current.

Furthermore, the element 18 is for stabilizing the set reference voltage (portion f).

As explained above, according to the device shown in FIG. 2, the diode bridge 13 is provided at the input stage to make it non-polar, and the connection of the terminals is reversed no matter which direction the DC motor 2a is driven to rotate. There's no need. Moreover, it is convenient because there is no need to pay attention to the connection direction of the terminals and there is no need to make mistakes in connection.

Further, the @ position shown in FIG. 2 has only two terminals for motor drive current as external terminals. That is, the circuit configuration does not require any special terminals for power supply, and since such terminals are not provided, wiring is extremely easy.

Next, a motor torque limiter according to a second embodiment will be explained using FIG. Compared to the device of the first embodiment, this device does not include the integrating circuit sections 5 and 6, but instead includes a timer circuit 19. In addition, current detection circuit 3a,
The amplifier section 4a, the comparator 7a, the switching circuit 9a, and the starting Ti flow trap circuit 11a are the width section 4 of the IIR flow ratio detection circuit 3 in the device of the first embodiment, respectively.
Comparator 7. The switching circuit 9 and the starting current trap circuit 11 have substantially the same circuit configuration.

The timer circuit 9 includes a comparator 7a and a switching circuit 9.
If it is determined that the DC motor 2 is overloaded according to the output signal from the comparator 7a, the switching circuit 9a is turned off for a certain period of time. As a result, power supply to the DC motor 2 is stopped for a certain period of time. The energization stop period in this timer circuit 19 is determined by the variable resistor 19
Adjusted by a, for example, several tens of seconds6tc to several hundred μse
It is set to about c.

By the way, when one energization stop period has elapsed, the DC motor 2 is energized again, but if it is determined that the overload condition of the motor 2 has not yet been released, the timer circuit 19 is activated again, and the DC motor 2 is de-energized again. Energization is stopped for the above-mentioned one energization stop period. Thereafter, as long as the overload state of the motor 2 is not canceled, the energization period and the de-energization period to the motor 2 are alternately formed. In addition, while the energization period at this time is approximately determined by the circuit configuration, the energization stop period can be changed by the variable resistor 19a, so that the so-called PPM (Pulsepostttt) of the motor torque can be changed.
on MOdtllatiOn ) control is performed, and when the motor 2 is in an overload state, the lower limit value of the effective torque of the motor can be maintained at a desired value.

Here, the above PPM 1blJ III is the ON state of the motor drive current.

The OFFFF opening period has changed to 11! IE
In this sense, it can be said to be a type of pulse width modulation. Further, this variable resistor 19a corresponds to the second setting sections 10a and 10b in the device of the first embodiment. Note that the variable resistor 8a that sets the upper limit value of the drive current of the motor 2 corresponds to the first ya constant part 8 in the device of the first embodiment.

Next, a third embodiment in which the motor torque limiter of the present invention is used in an AC motor will be described. The @ position according to this embodiment is formed by, for example, a circuit having a similar circuit configuration to that shown in FIG.

However, when the rectifier is disposed outside the device, the diode bridge 13 at the input stage becomes unnecessary.

Further, in the circuit shown in FIG. 2, it is more preferable to use an SCR or a triac in place of the Darlington connection transistor 14. In addition, in order to prevent noise generation due to the chopper, the switching circuit 9.9a
It is more preferable to adopt a configuration in which a zero cross circuit or a snubber circuit is added to the circuit.

In addition, when using a single-phase AC motor as an AC motor, it is sufficient to insert this torque limiter in series into one of the two AC lines connecting the motor and AC power supply, and when using a three-phase AC motor as an AC motor. When using an AC motor, the present torque limiter may be inserted in series into the AC lines of any two of the three phases.

In this manner, the motor torque limiter of the present invention is convenient in that it has the same circuit configuration regardless of whether it is used for a DC motor or an AC motor, and has versatility.

It should be noted that the motor torque limiter of the present invention is not necessarily limited to the circuit shown in the above embodiment, and may be formed using various other circuit configurations. For example, instead of the starting current trap cycle shown in FIG. 2, starting 1i! is comprised of a timer circuit that enables the comparator to operate only after a certain period of time r1 has elapsed since motor starting! A trap circuit may also be provided.

The motor torque limiter of the present invention can be used for all DC motors and AC motors, and can also be used for AC and DC motors such as universal motors.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a first embodiment of a motor torque limiter according to the present invention, FIG. 2 is a circuit diagram showing a specific circuit configuration of the torque limiter shown in FIG. 1, and FIG. FIG. 2 is a block diagram showing a second embodiment of the motor torque limiter according to the invention. i, Ia, 1b-...DC power supply 2.2a...DC motor 3.3a...NFE detection circuit 5...Charging II circuit section 6...Discharge integration circuit section 7.7a... Comparators 8, 8a...First setting section 9.9a...Switching circuits 10a, 10b, 19a -...Second i! Q constant section 11, 118...starting current trap circuit 12a,
12b...Terminal 19...Timer circuit 13...
・Diode bridge, Figure 3

Claims (1)

[Scope of Claims] 1) A torque limiter that is connected in series between a power source and a motor and limits the torque of the motor to a predetermined range by limiting the range of armature current flowing through the motor. The current supplied from the power source to the motor includes two terminals for connection to the motor, a first setting section for setting the upper limit of the current range, and a second setting section for setting the lower limit of the torque range. a current detection circuit that detects the current, a comparator that compares the output of this current detection circuit with the upper limit value set by the first setting section, and when the output of this comparator causes the current to exceed the upper limit value, the motor is controlled by pulse width modulation. a switching circuit that maintains the effective torque of the motor at a lower limit value set by the second setting section, and a starting current trap circuit that prevents the comparator or the switching circuit from operating depending on the starting current of the motor. Features: Torque limiter for motors. 2) A rectifier unit is connected to the two terminals to supply a current in a constant direction to the current detection circuit regardless of the direction of the armature current supplied to the motor. Torque limiter for the motor described in item 1. 3) The torque limiter for a motor according to claim 1 or 2, wherein the motor is a DC motor. 4) The torque limiter for a motor according to claim 1 or 2, wherein the motor is an AC motor.