Stepping Motor is a synchronous motor, stepping at the pulse frequency of the drive signal.
In order for the motor to move quickly, the stepping speed must be very fast.
However, due to the inertia of the motor and the load, the motor usually cannot reach the required number of revolutions per minute from 0 rpm step by step.
Therefore, most stepping motors receive drive from the pulse chain, which starts slowly and then increases the rate until the motor reaches the required rate.
To stop the motor, the drive signal must not stop suddenly; It must gradually decrease or decrease to zero.
The microprocessor can easily generate the desired ramp-up signal and then the ramp-down signal, commonly known as the trapezoidal profile, but it is difficult to generate the ramp in any circuit without the microprocessor.
The bistable circuit based on 555 in Fig. 1 can easily generate pseudo-trapezoidal motion curves.
Please note that the timing string of R 1 and its related components is not connected to v cc as in a normal circuit, but receives its power supply through a push button switch.
Fig. 1 this circuit generates a pseudo-trapezoidal motion control curve for controlling the stepping motor.
When the button is pressed, the capacitor C 1 starts charging until C 2 can start charging.
When C 1 is charged, the output frequency of 555 starts slowly and then gradually increases to the frequency or pulse frequency, which is a function of all components in the timing string.
If C 1 and R 1 are not in the string, the final frequency is lower than the frequency adopted by the circuit.
When the button is released, the 555 will not stop running immediately, but will gradually reduce the frequency until it finally stops (Figure 2a and 2b)).
The generated ramp frequency does not follow a linear curve, but the frequencies in most microprocessor-driven circuits do not follow a linear curve.
Depending on the component value, the ramp frequency curve of the circuit should be similar to Fig. 2a.
Fig. 2 the motion curve of the circuit in Fig. 1 is roughly trapezoidal (a);
The step rate curve shows a lower frequency when rising and falling (B).
You can operate the circuit with a simple button.
This concept opens up a world of manual control for stepping motors.
In general, stepping motors do not use manual control because it is difficult to generate trapezoidal frequency curves in hardware.
Using this circuit, you can use a stepping motor with low torque and low revolution per minute in a system that previously required a DC gearbox motor.
By changing the button to the dpdt switch, the stepper motor can be run clockwise and then counterclockwise without microprocessor control (Figure 3). ).
These concepts also apply to linear actuators based on stepping motors.
You can also replace the button with a control signal from a computer or controller, so that the stepping motor can obtain a driving force from a controller that does not have a built-in ramp generation function.
Fig. 3 by changing the button in Fig. 1 to dpdt switch, the stepping motor can run clockwise and then counterclockwise without microprocessor control. TAG