Medical Equipment
| ♦ Control by resistance |  |
| A resistor is placed in series between the power supply and the DC motor for restricting current by an increase in resistance to control the motor speed. The use of a variable resistor can vary the motor characteristics linearly control. | |
| ♦ Braking (Short-circuit brake) |  |
| A method to force the terminals of the DC motor to be shorted to stop the motor. This method can shorten the stopping motor time and provides powerful braking control. (Maximum braking when R = 0) |
♦ Bidirectional driving of DC motors by transistors
Bidirectional motor driving is achieved by switching the H-type bridge circuit by use of NPN and PNP transistors.
Bidirectional motor driving is achieved by switching the H-type bridge circuit by use of NPN and PNP transistors.
|
|
| Forward run when the upper left and lower right transistors are on. | Reverse run when the lower left and upper right transistors are on. |
♦ PWM control (pulse width modulation method)
The basic principle of control is to vary the average energy to control the speed by varying a ratio of "ON" and "OFF" of a pulse with the cycle keptconstant. For instance, when (a) and (b) are compared, (b) that has a higher duty ratio requires larger drive energy.
The basic principle of control is to vary the average energy to control the speed by varying a ratio of "ON" and "OFF" of a pulse with the cycle keptconstant. For instance, when (a) and (b) are compared, (b) that has a higher duty ratio requires larger drive energy.
|
|
|
| T-N characteristics during PWM control | Reference circuit diagram |
♦ Electric Noise Measures
When a DC brush motor rotates, spark current occurs due to switching of the commutator. This spark may become electric noise to adversely affect the control circuit. Such noise can be reduced by connecting a capacitor to the DC motor case.
(Note, however, when the motor is PWM-controlled, the frequency characteristics must be examined.)
When a DC brush motor rotates, spark current occurs due to switching of the commutator. This spark may become electric noise to adversely affect the control circuit. Such noise can be reduced by connecting a capacitor to the DC motor case.
(Note, however, when the motor is PWM-controlled, the frequency characteristics must be examined.)
