Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Reexamination Certificate
1999-05-21
2001-01-30
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
C318S519000, C318S568100
Reexamination Certificate
active
06181098
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC motor control circuit mounted in a serial printer and the like.
2. Description of the Related Art
There has been known a serial printer, in which a print head is driven by a DC motor for reciprocal movement during printing. Generally, the DC motor is controlled by a CPU provided in the printer. More specifically, positional information of the print head is obtained using a linear encoder or the like. The positional information is then supplied to the CPU so that the CPU can properly control the DC motor.
SUMMARY OF THE INVENTION
In a conceivable printer, the CPU determines the direction, in which the print head is desired to be moved, and the speed, at which the print head is desired to be moved. The CPU then performs control operation to move the print head in the desired direction and at the desired speed through executing interrupt processes described below.
That is, the linear encoder provided in the printer detects a movement of the print head, and outputs position detection signals. Every time the linear encoder issues a position detection signal, the position detection signal is supplied as an interrupt request signal to the CPU, whereupon the CPU executes an interrupt process to perform various processings. That is, during the interrupt process, the CPU determines the direction in which the print head is actually moving. The CPU increments or decrements its internal counter based on the determined direction, thereby producing a position count value indicative of the present position of the print head. The CPU controls start/stop operation of a timer to measure the period of time between the successively-executed interrupt processes. This measured period of time represents a speed, at which the print head is moving. The CPU compares the measured speed with the desired speed to be attained. Based on the compared result, the CPU increases or decreases the amount of an electric current flowing through the DC motor, thereby controlling the print head to move stably at the desired speed. The CPU also judges whether the print head reaches a predetermined stop position. When the CPU determines that the print head reaches the predetermined stop position, the CPU performs a braking operation to immediately stop the print head at the predetermined stop position. That is, the CPU stops the DC motor by outputting a stop signal to the DC motor. The CPU further judges whether or not the print head has stopped by investigating the state how the position count value changes. When the CPU determines that the print head has stopped properly at the predetermined stop position, the CPU then controls the DC motor to drive in an opposite rotational direction, thereby moving the print head to move in the opposite direction. The CPU can also determine that the print head has stopped for some trouble when the position count value does not change in conformity to the desired direction, in which the CPU has controlled the print head to move. When the CPU determines that the print head has stopped for some trouble, the CPU performs a predetermined error process.
While controlling movement of the print head as described above, the CPU also controls printing operation of the print head.
It is noted that the CPU performs the above-described control operations by executing a software program. In order to enhance the processing capability of the CPU, it is conceivable to provide a hardware circuit structure, shown in
FIG. 1
, that supplements or assists the above-described control operation of the CPU.
The hardware circuit structure of
FIG. 1
is provided to obtain the position count value (positional information) of the print head by determining the direction, in which the print head is presently moving. The hardware circuit structure of
FIG. 1
includes a position detection signal processing circuit
101
and a position count processing circuit
104
. The position detection signal processing circuit
101
is connected to the linear encoder (not shown in the drawings). The linear encoder detects the movement of the print head, and outputs two position detection signals A and B, accordingly. The position detection signal processing circuit
101
receives the position detection signals A and B, and converts the signals A and B into a position count signal
102
and a direction distinction signal
103
in a manner shown in FIG.
2
.
That is, when the position detection signal A rises while the position detection signal B is in a high condition, then the position detection signal processing circuit
101
outputs one pulse of the position count signal
102
, and simultaneously inverts the direction distinction signal
103
to a high condition. On the other hand, when the position detection signal A falls while the position detection signal B is in a high condition, the position detection signal processing circuit
101
outputs one pulse of the position count signal
102
, and simultaneously inverts the direction distinction signal
103
to a low condition.
The position count processing circuit
104
is for receiving the position count signal
102
and the direction distinction signal
103
, and for outputting a position count value
105
depending on the position count signal
102
and the direction distinction signal
103
. More specifically, when the position count signal
102
is inputted while the direction distinction signal
103
is in a high condition, the position count processing circuit
104
increments its internal counter value by one. On the other hand, when the position count signal
102
is inputted while the direction distinction signal
103
is in a low condition, the position count processing circuit
104
decrements the internal counter value by one. By referring to the internal counter value, the position count processing circuit
104
outputs a position count value
105
indicative of the print head movement position. It is noted that in this example of
FIG. 2
, an initial value of the internal counter of the position count processing circuit
104
is set to “100”.
In this case, the CPU (not shown) controls movement of the print head based on the position count value
105
. For example, when the position count value
105
reaches the predetermined value while the DC motor is being driven, the position count processing circuit
104
outputs an interrupt request signal to the CPU. As a result, the CPU performs an interrupt process for performing stopping processes to stop the DC motor by outputting a stop signal to the DC motor. When the DC motor is properly stopped, the CPU then controls the DC motor to drive in an opposite rotational direction. The CPU controls the print head to perform printing while moving the print head in the opposite direction.
Additionally, each time the position count signal
102
is outputted from the position detection signal processing circuit
101
, the position count processing circuit
104
controls the CPU to execute another interrupt process. Each time the CPU performs the interrupt routine, the CPU confirms whether the position count value
105
has increased or decreased, so as to judge whether the print head has stopped due to some trouble. When the CPU judges that the print head has stopped for some unscheduled reason, the CPU performs the predetermined error process.
However, even though the above-described hardware circuitry of
FIG. 1
is used, the DC motor is controlled to be stopped according to the interrupt routine performed by the CPU. A timing, at which the interrupt routine is executed, changes depending on other processes the CPU is performing. Accordingly, the processes for stopping the DC motor can not be performed at a uniform timing. As a result, the print head can not stop at the desired fixed stop position.
In addition, in order to detect whether the print head has stopped due to some trouble, the CPU has to perform the interrupt routine each time the position detection signal processing circuit
101
outputs the position count signal
10
Brother Kogyo Kabushiki Kaisha
Leykin Rita
Nappi Robert E.
Oliff & Berridg,e PLC
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