Pulse Motor Driving Apparatus

1. Field of the Invention

The present invention generally relates to a pulse motor driving apparatus. More particularly, the present invention is directed to such pulse motor driving apparatus which can improve the stability of stepping revolution at the time of low revolution speed and which can also assure a high revolution whenever it is wished.

2. Description of the Prior Art

For the pulse motor used for driving a carriage of printing head in a printer it is generally required that at the time of the printing operation phase a stable and low speed stepping revolution can be obtained on one hand and at the time of the quick drive phase or carriage return a possible higher revolution can be obtained, on the other hand. Hitherto, many attempts have been made to satisfy the requirement. However, all the solutions already proposed have led to a substantial increase in size of the pulse motor itself as well as in its manufacturing cost.

Accordingly, it is an object of the invention to provide a pulse motor driving apparatus which improves the stability of pulse motor operation at the time of low revolution and also enables a high revolution of the pulse motor when necessary.

It is another object of the invention to provide a pulse motor which is small in size and low in manufacturing cost.

It is a further object of the invention to provide a driving apparatus which is adaptable for driving a printer head carriage and which has a high performance required for this purpose.

Other and further objects, features and advantages of the invention will appear more fully from the following description taken in connection with the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the invention;

FIG. 2(a) is a circuit diagram showing an equivalent circuit in the embodiment at its low revolution phase of operation;

FIG. 2(b) is a circuit diagram showing an equivalent circuit in the embodiment for enabling a high revolution;

FIG. 3 is a circuit diagram showing a second embodiment of the invention; and

FIG. 4 is a circuit diagram showing an equivalent circuit of the second embodiment.

Referring first to FIG. 1 showing a first embodiment comprising, as an example, a four-phase pulse motor, L.sub.1, L.sub.2, L.sub.3 and L.sub.4 designate the windings of the pulse motor. On the non-ground side, the terminals of the windings are connected to a winding excitation power source E. On the ground side, terminals of the windings are grounded through switching transistors Tr.sub.1, Tr.sub.2, Tr.sub.3 and Tr.sub.4 respectively.

By sequentially applying control pulse signals to input terminals 1, 2, 3 and 4 at the gate side of the transistors Tr.sub.1, Tr.sub.2, Tr.sub.3 and Tr.sub.4, the windings L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are excited so that the output shaft of the pulse motor may be brought into rotation.

The ground side terminals of the windings L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are also connected to the anode side terminals of diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 respectively the cathode side terminals of which are connected to the winding excitation power source E through a control transistor Tr.sub.5. Connected between the emitter-collector of the control transistor Tr.sub.5 is a control resistor R. If desired, the control transistor Tr.sub.5 may be replaced by a lead switch.

The manner of operation of the above first embodiment is as follows:

During the phase of lower revolution such as the time of printing being effected in a printer, the input terminal 5 at the gate side of the control transistor Tr.sub.5 receives a signal which serves to turn the transistor Tr.sub.5 on. In this position, the excitation circuit of each winding of the pulse motor may be represented by an equivalent circuit shown in FIG. 2(a). In FIG. 2A, the winding L is excited by closing the switch S (switching transistor). When the switch is opened thereafter, there is produced a back electromotive force between the terminals A and B, which serves to brake the rotation of the pulse motor. Therefore, a sure stepping revolution of the pulse motor is attainable at the time of relatively low revolution.

On the contrary, during the phase of higher revolution such as the time of quick drive of printer or carriage return, no signal is applied to the input terminal at the gate side of the control transistor Tr.sub.5 and therefore there is formed an equivalent circuit as shown in FIG. 2(b). In the position shown in FIG. 2(b) the winding L is excited by closing the switch S in the same manner as in FIG. 2(a). However, in case the of FIG. 2(b) circuit, the back electromotive force produced between the terminals A and B by opening the switch S is consumed in the control resistor R. This reduces the above mentioned braking effect and therefore the pulse motor is allowed to speed up its stepping rotation so as to follow the high speed switching operations of transistors Tr.sub.1, Tr.sub.2, Tr.sub.3 and Tr.sub.4 shown in FIG. 1.

FIG. 3 shows a second embodiment of the present invention which again comprises, as an example, a four-phase pulse motor.

In FIG. 3, the windings L.sub.1, L.sub.2, L.sub.3 and L.sub.4 of the pulse motor have terminals connected to a winding excitation power source E at non-ground side. At ground side, the other terminals of the windings L.sub.1, L.sub.2 L.sub.3 and L.sub.4 are grounded through switching transistors Tr.sub.1, Tr.sub.2, Tr.sub.3 and Tr.sub.4 respectively.

By applying control pulse signals sequentially to the input terminals 1, 2, 3 and 4 at the gate side of the switching transistors Tr.sub.1, Tr.sub.2, Tr.sub.3 and Tr.sub.4 the windings L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are excited so that the output shaft of the pulse motor may be brought into rotation.

The ground side terminals of the windings L.sub.1, L.sub.2, L.sub.3 and L.sub.4 are also connected to the emitter side terminals of control transistors Tr.sub.6, Tr.sub.7, Tr.sub.8 and Tr.sub.9 the collector side terminals of which are connected to the power source E.

The manner of operation of the second embodiment is as follows:

During the phase of relatively low revolution such as the time of printing being effected, a signal is applied to an input terminal 5a at gate side. The input terminal 5a is common to all the control transistors Tr.sub.6, Tr.sub.7, Tr.sub.8 and Tr.sub.9 and the signal applied to the common terminal is such signal which serves to turn the control transistors on. The equivalent circuit shown in FIG. 4 represents the excitation circuit of each winding of the pulse motor.

In the position shown in FIG. 4, the winding L is excited by closing the switch S (switching transistor). When the switch S is opened thereafter, a back electromotive force is produced between the terminals A and B. This will serve as a brake to the rotation of the pulse motor provided that the input terminal 5a at the gate side of the control transistor Tr is receiving at that time a signal which renders the transistor Tr conductive. Therefore, in this manner, a stable and sure stepping rotation of the pulse motor can be attained at the time of relatively low revolution.

On the contrary, during the phase of high revolution such as a quick drive of a printer or carriage return, there is applied to the input terminal 5a such signal which makes the transistor Tr equivalent to the resistor R shown in FIG. 2B. Under this condition, the back electromotive force produced between the terminals A and B by opening the switch S will be consumed in the equivalent resistor R of the control transistor Tr. Therefore, the braking effect is reduced accordingly. Thus, the pulse motor is allowed to speed up its stepping rotation so as to follow the high speed switching operations of transistors Tr.sub.6, Tr.sub.7, Tr.sub.8 and Tr.sub.9. Furthermore, there is provided the possibility of setting various steps of high revolution by applying an optional signal to the input terminal 5a.

As will be understood from the above embodiments, the driving apparatus according to the invention is very simple in circuit arrangement and is adaptable for a conventional small and inexpensive pulse motor for use in a printer without need of extensive change in design and size of the pulse motor. By employing the arrangement of the invention, the maximum performance is attainable over the entire range from low revolution to high revolution required to move a printing head carriage in a printer while holding the merit of small size of the pulse motor.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details can be made therein without departing from the spirit and scope of the invention.