| 摘要 |
<p>1514202 Control of stepper motors TEXAS INSTRUMENTS Inc 11 March 1975 [18 March 1974] 10049/75 Heading H2J A switching regulator control circuit for a multi-coil stepper motor comprises means to selectively provide an enable signal to select each coil; a feedback circuit connected to the selected coil; comparator means, having one input to receive a signal from the feedback circuit and a second input to receive an input signal level, to provide a desired voltage output signal when the feedback signal and the input signal level reach a prescribed difference in magnitude, enabling means connected to receive the enable signals and the output of the comparator means and responsive to each of the enable signals to select a current path through a selected motor coil; and drive circuit means connected to respond to the enabling means and connected to the motor coils to provide current to the selected coil, the energy stored in the latter being used to reduce the current drawn from the drive circuit means and the circuit providing a controlled average coil current that is dependent on the characteristics of the individual coil. Fig. 2 shows a control circuit 30 for the coils A, B, C of a stepper motor driving a thermal printhead, each coil having an identical enabling and drive circuit 31, 32, 33 controlled by a comparator 38, one input of which receives a logic 1 or 0 signal from terminal 37 and the other input of which receives a triangular waveform signal generated by circuit 40, 41, 42, 43 connected to clock signal input 39. Enabling signals are applied at terminals 34, 35, 36, a typical energization of coil A being as follows:- (1) A logic 1 signal is continuously applied to comparator 38 and an enable signal to terminal 34 whereby, when the comparator input at 43 is less than the logic 1 signal, NAND gate 51 switches on transistors 53, 60, 61 to energize coil A. (2) The coil current produces a feedback voltage across resistor 45, which voltage is added to the triangular signal. (3) When the input at 43 exceeds the logic 1 signal, the comparator output changes to cause gate 51 to switch off transistors 53, 60, 61, whereupon the energy in coil A is discharged through the circuit 45, 58, 59 to prolong the coil current and protect transistor 61. The resistor 59 has counterparts (not shown) for the diodes (58) of the other two coils B and C and has a value such that the coil discharge time is very long with respect to the period of the triangular signal. Hence the coil discharge is not completed when the next coil is selected, thus providing smooth motor start-up. A plurality of coils may be simultaneously energized to produce a braking action.</p> |
