Motor control system and image forming apparatus using the same

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a motor control system, and more particularly to a motor control system in which a plurality of electric motors can be controlled by a single MPU (microprocessor unit). This invention further relates to an image forming apparatus using such a motor control system.

2. Description of the Related Art

FIG. 7

shows a typical conventional motor control circuit. Motor control circuits using a MPU

50

are broadly divided into a constant-current system motor control circuit and a constant-voltage system motor control circuit. The motor control circuit shown in

FIG. 7

is of a constant-current system. In the motor control circuit, pulse motors PM (PM

1

, PM

2

and PM

3

) are driven under the control of control signals which are respectively input into drivers

51

(driver

1

, driver

2

and driver

3

) each having a clock terminal CLK (CLK

1

, CLK

2

, CLK

3

) through which a clock for controlling the rotating speed of the motor is input, an enabling terminal ENB (ENB

1

, ENB

2

, ENB

3

) for controlling whether the motor is to be rotated, and a clockwise/counterclockwise terminal CW/CCW (CW/CCW

1

, CW/CCW

2

, CW/CCW

3

).

As shown in

FIG. 7

, when a plurality of pulse motors PM

1

to PM

3

are controlled by a single MPU

50

, control signals for the respective motors PM

1

to PM

3

are discretely connected to the MPU

50

.

When the MPU

50

has a built-in clock generation means such as an integrated timer controller ITC, pulse motors more than the number of channels which the built-in integrated timer controller ITC can use cannot be controlled unless an additional integrated timer controller

52

is provided. For example, in the example shown in

FIG. 7

, the third motor PM

3

is controlled by the additional integrated timer controller

52

.

Such an additional integrated timer controller adds to cost and requires an additional space on the circuit board, which adds to the size of the circuit board.

Generally the MPU

50

is provided with an integrated timer controller ITC having a plurality of channels. When the MPU

50

is incorporated in an apparatus having various mechanisms and processing means (e.g., an image forming apparatus to be described later), all the channels of the integrated timer controller cannot be used for controlling the motors but a part of the channels must be used for controlling other mechanisms and/or the processing means in the apparatus, which gives rise to the aforesaid problem.

For example, in a stencil printer as an example of the image forming apparatus, the number of objects to be controlled by the MPU has been increasing as the number of automated functions of the printer is increased. For example, in the current stencil printer, a large number of motors including those for adjusting the printing position on the printing paper in the longitudinal direction and the transverse direction, for supplying printing papers, and discharging printing papers are incorporated.

Though a plurality of MPU's have been incorporated in the current stencil printer by the function, increasing objects to be controlled has come to require additional integrated timer controllers.

SUMMARY OF THE INVENTION

In view of the foregoing observations and description, the primary object of the present invention is to provide a motor control system which can control motors larger in number than the number of the channels of the timer controller for generating clocks without increasing a timer controller.

Another object of the present invention is to provide an image forming apparatus employing such a motor control system.

In accordance with a first aspect of the present invention, there is provided a motor control system comprising

a processor having a clock output terminal for outputting clock pulses in desired cycles,

a plurality of motors, and

a plurality of motor drivers which are provided one for each motor and drive the corresponding motors on the basis of the clock pulses input into the motor drivers through respective clock input terminals thereof,

wherein the improvement comprises that the clock input terminals of the motor drivers are connected to the clock output terminal of the processor in common with each other.

In one embodiment of the present invention, the processor outputs an enabling signal exclusively to one of the motor drivers, thereby enabling said one motor driver to start driving the corresponding motor.

In another embodiment, the processor outputs an enabling signal to two or more of the motor drivers at one time, thereby enabling the motor drivers to start driving the corresponding motors.

In accordance with a second aspect of the present invention, there is provided a motor control system comprising

a processor having first and second clock output terminals and a plurality of enabling signal output terminals, the first and second clock output terminals outputting first and second clock pulses in desired cycles and in phases different from each other by a predetermined amount,

a plurality of motors, and

a plurality of motor drivers which are provided one for each motor and drive the corresponding motors in a constant-voltage drive mode on the basis of the first and second clock pulses input into the motor drivers from the first and second clock output terminals through first and second clock input terminals of each of the motor drivers and the enabling signals selectively input into the motor drivers through the enabling signal output terminals of the processor,

wherein the improvement comprises that the first clock input terminals of the motor drivers are connected to the first clock output terminal of the processor in common with each other, and the second clock input terminals of the motor drivers are connected to the second clock output terminal of the processor in common with each other.

In accordance with a third aspect of the present invention, there is provided a motor control system comprising

a processor having a clock output terminal, a plurality of enabling signal output terminals, and a plurality of rotating direction signal output terminals, the clock output terminal outputting clock pulses in desired cycles,

a plurality of motors, and

a plurality of motor drivers which are provided one for each motor and drive the corresponding motors in a constant-current drive mode on the basis of the clock pulses input into the motor drivers from the clock output terminals through a clock input terminal of each of the motor drivers and the enabling signals and the rotating direction output signals selectively input into the motor drivers respectively through the enabling signal output terminals and the rotating direction output terminals of the processor,

wherein the improvement comprises that the clock input terminals of the motor drivers are connected to the clock output terminal of the processor in common with each other.

In accordance with a fourth aspect of the present invention, there is provided an image forming apparatus which is for forming an image on a printing paper and is provided with a plurality of motors and a motor control system for controlling the motors, the motor control system comprising

a processor having a clock output terminal for outputting clock pulses in desired cycles, and

a plurality of motor drivers which are provided one for each motor and drive the corresponding motors on the basis of the clock pulses input into the motor drivers through respective clock input terminals thereof,

wherein the improvement comprises that the clock input terminals of the motor drivers are connected to the clock output terminal of the processor in common with each other.

The motors may be, for instance, those for adjusting the position on the printing paper in which the image is to be formed.

In accordance with the present invention, since a plurality of motor drivers use one channel of an integrated timer controller of the processor in common with each other, more motors than the number of the available channels of the integrated timer controller can be controlled by the processor without increasing an integrated timer controller.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a block diagram showing a motor control system in accordance with a first embodiment of the present invention,

FIG. 2

is a block diagram showing a motor control system in accordance with a second embodiment of the present invention,

FIG. 3A

is a plan view of a stencil printer provided with a motor control system in accordance with the present invention,

FIG. 3B

is a front view of the stencil printer,

FIG. 4

is a view for illustrating adjustment of the printing position on the printing paper,

FIG. 5

is a view showing the control panel of the stencil printer,

FIG. 6

is a flow chart for illustrating the processing of adjusting the printing position on the printing paper, and

FIG. 7

is a block diagram showing a conventional motor control system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1

shows a motor control system in accordance with a first embodiment of the present invention which drives a plurality of electric motors in a constant-voltage drive mode.

In

FIG. 1

, an MPU

1

has a three-channel input-output unit I/O and a two-channel integrated timer controller ITC and controls three pulse motors PM

1

to PM

3

by way of first to third motor drivers

5

a

to

5

c.

The motor drivers

5

a

to

5

c

are respectively provided with enabling signal input terminals ENB

1

′ to ENB

3

′ and the enabling signal input terminals ENB

1

′ to ENB

3

′ are separately connected to enabling signal output terminals ENB

1

to ENB

3

of the input-output unit I/O of the MPU

1

.

The integrated timer controller ITC of the MPU

1

has first and second clock output terminals CLK

1

and CLK

2

. Each of the motor drivers

5

a

to

5

c

is provided with first and second clock input terminals CLK

1

′ and CLK

2

′. The first clock input terminals CLK

1

′ of the respective motor drivers

5

a

to

5

c

are connected to the first clock output terminal CLK

1

of the integrated timer controller ITC of the MPU

1

in common with each other and the second clock input terminals CLK

2

′ of the respective motor drivers

5

a

to

5

c

are connected to the second clock output terminals CLK

2

of the integrated timer controller ITC of the MPU

1

in common with each other.

The first and second clock output terminals CLK

1

and CLK

2

output clock pulses which are the same in frequency and different in phase by a predetermined amount (90°) from each other.

The MPU

1

selectively inputs an enabling signal to one or more of the motor drivers

5

a

to

5

c

and only the motor driver(s) which receives the enabling signal is selectively operated. The selected motor driver(s) drives the corresponding pulse motor(s) at a speed corresponding to the clock pulses output from the clock output terminal CLK

1

or CLK

2

in the direction (clockwise direction or counterclockwise direction) corresponding to the phase difference between the clock pulses output from the first and second clock output terminals CLK

1

and CLK

2

, that is, depending on which is output earlier.

When the enabling signal is input into one of the motor drivers

5

a

to

5

c

, only the pulse motor corresponding to the motor driver which receives the enabling signal is exclusively driven. (exclusive control)

When the enabling signal is input into two or more motor drivers, the pulse motors corresponding to the motor drivers which receive the enabling signal are all driven at the same speed in the same direction. (simultaneous control)

In the case of the simultaneous control, the mechanisms to be driven by the pulse motors can be moved at different speeds even if the rotating speeds of the pulse motors are the same by inserting a gear mechanism between the pulse motor and the mechanism to be driven by the pulse motor.

FIG. 2

shows a motor control system in accordance with a second embodiment of the present invention which drives a plurality of electric motors in a constant-current drive mode.

In

FIG. 2

, an MPU

1

has a three-channel input-output unit I/O and a two-channel integrated timer controller ITC and controls three pulse motors PM

1

to PM

3

by way of first to third motor drivers

5

a

to

5

c.

The motor drivers

5

a

to

5

c

are respectively provided with enabling signal input terminals ENB

1

′ to ENB

3

′ and the enabling signal input terminals ENB

1

′ to ENB

3

′ are separately connected to enabling signal output terminals ENB

1

to ENB

3

of the input-output unit I/O of the MPU

1

. Further the motor drivers

5

a

to

5

c

are respectively provided with rotating direction signal input terminals CW/CCW

1

′ to CW/CCW

3

′ and the enabling signal input terminals CW/CCW

1

′ to CW/CCW

3

′ are separately connected to rotating direction signal output terminals CW/CCW

1

to CW/CCW

3

of the input-output unit I/O of the MPU

1

.

The integrated timer controller ITC of the MPU

1

has first and second clock output terminals CLK

1

and CLK

2

. The first motor driver

5

a

is provided with a single clock input terminal CLK

1

′ and each of the second and third motor drivers

5

b

and

5

c

is provided with a single clock input terminal CLK

2

′. The clock input terminal CLK

1

′ of the first motor driver

5

a

is connected to the first clock output terminal CLK

1

of the integrated timer controller ITC of the MPU

1

separately from the clock input terminals CLK

2

of the second and third motor drivers

5

b

and

5

c

, whereas the clock input terminals CLK

2

′ of the second and third motor drivers

5

b

and

5

c

are connected to the second clock output terminal CLK

2

of the integrated timer controller ITC of the MPU

1

in common with each other.

With this arrangement, the pulse motor PM

1

driven by the first motor driver

5

a

is controlled independently of the second and third pulse motors PM

2

and PM

3

, whereas pulse motors PM

2

and PM

3

driven by the second and third motor drivers

5

b

and

5

c

use the single second clock output terminal CLK

2

of the MPU

1

in common with each other.

However the directions of rotation of the pulse motors PM

2

and PM

3

can be independently controlled by the rotating direction signals input from the rotating direction signal output terminals CW/CCW

2

and CW/CCW

3

, and also whether the pulse motors PM

2

and PM

3

are rotated or stopped can be independently controlled by the enabling signals input from the enabling signal output terminals ENB

2

and ENB

3

.

A stencil printer

10

in accordance with a third embodiment of the present invention, where a motor control system of the present invention is employed, will be described with reference to

FIGS. 3A and 3B

, hereinbelow.

In

FIGS. 3A and 3B

, the stencil printer

10

has a printing drum

11

around which a stencil master (not shown) is wound. A squeegee roller (not shown) which is in contact with the inner surface of the peripheral wall of the printing drum

11

and a doctor roller which supplies printing ink to the squeegee roller are provided inside the printing drum

11

. A press roller

13

is disposed just below the printing drum

11

to be movable up and down between an operative position in which it abuts against the outer peripheral surface of the printing drum

11

and a retracted position in which it is away from the outer peripheral surface of the printing drum

11

.

The printing drum

11

is rotated in the counterclockwise direction as seen in

FIG. 3B. A

paper supply table

12

a

on which a plurality of printing papers P are stacked is disposed on the left side of the printing drum

11

. A scraper unit

12

which feeds out the printing papers P one by one toward the printing drum

11

from the paper supply table

12

a

is disposed above the paper supply table

12

a.

A paper discharge portion

14

comprising a conveyor belt which conveys printed papers P separated from the printing drum

11

and a paper discharge table on which the printed papers P conveyed by the conveyor belt are stacked is disposed on the right side of the printing drum

11

.

The stencil printer

10

is provided with a longitudinal printing position adjustment mechanism and a transverse printing position adjustment mechanism. The longitudinal printing position adjustment mechanism adjusts the position of the stencil master on the printing drum

11

relative to the printing paper P in the longitudinal direction thereof (the direction of conveyance of the printing paper P), and the transverse printing position adjustment mechanism adjusts the position of the stencil master on the printing drum

11

relative to the printing paper P in the transverse direction thereof (a direction perpendicular to the direction of conveyance of the printing paper P). The longitudinal and transverse printing position adjustment mechanisms are driven by electric motors and are operated before the printing step. These motors may be controlled by the motor control system similar to the second embodiment shown in FIG.

2

. The motor for the longitudinal printing position adjustment mechanism will be referred to as “the longitudinal position adjustment pulse motor PM

2

” and the motor for the transverse printing position adjustment mechanism will be referred to as “the transverse position adjustment pulse motor PM

3

”, hereinbelow.

Adjustment of the position of the stencil master relative to the printing paper P in the longitudinal direction (upward or downward) is made by driving the longitudinal position adjustment pulse motor PM

2

to change the angular position of the printing drum

11

relative to the printing paper P which is supplied to the printing drum

11

at a predetermined timing.

Adjustment of position of the stencil master relative to the printing paper P in the transverse direction (rightward or leftward) is made by driving the transverse position adjustment pulse motor PM

3

to displace the paper supply table

12

a

rightward or leftward relatively to the printing drum

11

.

In

FIG. 4

, the area circumscribed by the broken line represents the effective image area on the stencil master. In the adjustment of the stencil master relative to the printing paper P in the longitudinal direction, the effective area is shifted upward or downward, and in the adjustment of the stencil master relative to the printing paper P in the transverse direction, the effective area is shifted rightward or leftward.

The operator carries out the printing position adjustment by operating longitudinal position adjustment keys

20

a

to

20

c

and transverse position adjustment keys

24

a

to

24

c

on the control panel

15

of the stencil printer

10

shown in FIG.

5

.

When the key

20

a

is pushed, the longitudinal position adjustment pulse motor PM

2

is rotated in the counterclockwise direction to shift upward the effective image area relatively to the printing paper P, and when the key

20

c

is pushed, the pulse motor PM

2

is rotated in the clockwise direction to shift downward the effective image area relatively to the printing paper P. An LED display

21

shows the selected position. When the key

20

b

is pushed, the effective image area is centered. The key

20

b

will be sometimes referred to as “the centering key

20

b”.

When the key

24

a

is pushed, the transverse position adjustment pulse motor PM

3

is rotated in the counterclockwise direction to shift leftward the effective image area relatively to the printing paper P, and when the key

24

c

is pushed, the pulse motor PM

3

is rotated in the clockwise direction to shift rightward the effective image area relatively to the printing paper P. An LED display

25

shows the selected position. When the key

24

b

is pushed, the effective image area is centered. The key

24

b

will be sometimes referred to as “the centering key

24

b”.

In this particular embodiment, the MPU

1

(

FIG. 2

) has a four-channel integrated timer controller ITC. Two of the four channels of the integrated timer controller ITC are used for a counter, a timer and the like for performing printing operation, another channel of the integrated timer controller ITC is used for driving a pulse motor of another mechanism. The other channel of the integrated timer controller ITC, that is, the clock output terminal CLK

2

is used by the longitudinal position adjustment pulse motor PM

2

and the transverse position adjustment pulse motor PM

3

in common with each other.

Thus, three pulse motors can be controlled by only two channels of the integrated timer controller ITC without use of an additional integrated timer controller ITC.

FIG. 6

shows a flow chart of interruption handling routine for executing the longitudinal printing position adjustment and the transverse printing position adjustment. In this flow chart, one of the pulse motors PM

2

and PM

3

is driven at one time. (exclusive control)

That is, operation of the longitudinal position adjustment keys

20

a

to

20

c

and operation of the transverse position adjustment keys

24

a

to

24

c

are alternately allowed and are not simultaneously allowed.

When one of the longitudinal position adjustment keys

20

a

and

20

c

is pushed (when the answer to the question in step S

1

is YES), the MPU

1

outputs through the clock output terminal CLK

2

clock pulses at a frequency suitable for rotating the longitudinal position adjustment pulse motor PM

2

at a predetermined speed. (step S

4

)

Then it is determined whether the key

20

a

has been pushed. (step S

5

) When it is determined that the key

20

a

has been pushed (when the answer to the question in step S

5

is YES), the MPU

1

outputs a rotating direction signal CCW

2

, representing that the position adjustment pulse motor PM

2

is to be rotated in the counterclockwise direction, through the rotating direction signal output terminals CW/CCW

2

(step S

6

) and outputs an enabling signal through the enabling signal output terminal ENB

2

(step S

8

).

Upon receipt of the rotating direction signal CCW

2

and the enabling signal, the second motor driver

5

b

rotates the longitudinal position adjustment pulse motor PM

2

in the counterclockwise direction until the key

20

a

is released. When the key

20

a

is released (when the answer to the question in step S

9

is YES), the enabling signal is made ineffective and the longitudinal position adjustment pulse motor PM

2

is stopped. (step S

10

)

When it is determined in step S

5

that the key

20

c

has been pushed (when the answer to the question in step S

5

is NO), the MPU

1

outputs a rotating direction signal CW

2

, representing that the position adjustment pulse motor PM

2

is to be rotated in the clockwise direction, through the rotating direction signal output terminals CW/CCW

2

(step S

7

) and outputs an enabling signal through the enabling signal output terminal ENB

2

(step S

8

).

Upon receipt of the rotating direction signal CW

2

and the enabling signal, the second motor driver

5

b

rotates the longitudinal position adjustment pulse motor PM

2

in the clockwise direction until the key

20

c

is released. When the key

20

c

is released (when the answer to the question in step S

9

is YES), the enabling signal is made ineffective and the longitudinal position adjustment pulse motor PM

2

is stopped. (step S

10

)

The amount of adjustment in the longitudinal direction is shown by the LED display

21

and is stored in the MPU

1

.

When one of the transverse position adjustment keys

24

a

and

24

c

is pushed (when the answer to the question in step S

1

is NO and the answer to the question in step S

2

is YES), the MPU

1

outputs through the clock output terminal CLK

2

clock pulses at a frequency suitable for rotating the transverse position adjustment pulse motor PM

3

at a predetermined speed. (step S

13

)

Then it is determined whether the key

24

a

has been pushed. (step S

14

) When it is determined that the key

24

a

has been pushed (when the answer to the question in step S

14

is YES), the MPU

1

outputs a rotating direction signal CCW

3

, representing that the position adjustment pulse motor PM

3

is to be rotated in the counterclockwise direction, through the rotating direction signal output terminals CW/CCW

23

(step S

15

) and outputs an enabling signal through the enabling signal output terminal ENB

3

(step S

17

).

Upon receipt of the rotating direction signal CCW

3

and the enabling signal, the third motor driver

5

c

rotates the transverse position adjustment pulse motor PM

3

in the counterclockwise direction until the key

24

a

is released. When the key

24

a

is released (when the answer to the question in step S

18

is YES), the enabling signal is made ineffective and the transverse position adjustment pulse motor PM

3

is stopped. (step S

19

)

When it is determined in step S

5

that the key

24

c

has been pushed (when the answer to the question in step S

14

is NO), the MPU

1

outputs a rotating direction signal CW

3

, representing that the position adjustment pulse motor PM

2

is to be rotated in the clockwise direction, through the rotating direction signal output terminals CW/CCW

3

(step S

16

) and outputs an enabling signal through the enabling signal output terminal ENB

3

(step S

17

).

Upon receipt of the rotating direction signal CW

3

and the enabling signal, the third motor driver

5

c

rotates the transverse position adjustment pulse motor PM

3

in the clockwise direction until the key

24

c

is released. When the key

24

c

is released (when the answer to the question in step S

18

is YES), the enabling signal is made ineffective and the transverse position adjustment pulse motor PM

3

is stopped. (step S

19

)

The amount of adjustment in the transverse direction is shown by the LED display

25

and is stored in the MPU

1

.

When one of the centering keys

20

b

and

24

b

is pushed (when the answer to the question in step S

1

is NO, the answer to the question in step S

2

is NO, and the answer to the question in step S

3

is YES), it is determined whether the centering key

20

b

for centering the printing position in the longitudinal direction has been pushed. (step S

21

) When it is determined that the key

20

b

has been pushed (when the answer to the question instep S

21

is YES), the MPU

1

controls the longitudinal position adjustment pulse motor PM

2

to center the printing position in the longitudinal direction. (step S

22

) That is, the MPU

1

stores therein the current printing position in the longitudinal direction and outputs a rotating direction signal CW

2

or CCW

2

, an enabling signal, and clock pulses to the second motor driver

5

b

so that the printing position is centered in the longitudinal direction.

When it is determined that the key

24

b

has been pushed (when the answer to the question in step S

21

is NO), the MPU

1

controls the transverse position adjustment pulse motor PM

3

to center the printing position in the transverse direction. (step S

24

) That is, the MPU

1

stores therein the current printing position in the transverse direction and outputs a rotating direction signal CW

3

or CCW

3

, an enabling signal, and clock pulses to the third motor driver

5

c

so that the printing position is centered in the transverse direction.

The processing described above is repeatedly executed as interruption processing while the power source of the stencil printer

10

is on.

Though, in the embodiment described above, the pulse motors PM

2

and PM

3

are controlled in exclusive control mode, the pulse motors PM

2

and PM

3

may be simultaneously driven. In such a case, clock pulses of the same frequency are supplied to the pulse motors PM

2

and PM

3

, and they are rotated at the same speed so long as they are of the same type.

In this case, the printing position is adjusted in both the longitudinal and transverse directions at one time. However since the mechanisms driven by the pulse motors PM

2

and PM

3

are different from each other, there arises no problem.

Though, in the third embodiment described above, the motor control system of the present invention is applied to a stencil printer as an image forming apparatus, the image forming apparatus need not be limited to the stencil printer.

Further, though, in the embodiments described above, pulse motors are employed, electric motors other than pulse motors may be employed. For example, in the case of the first embodiment, where the motors are driven in a constant-voltage mode, DC motors can be employed.

Further, as the means for generating clock pulses inside the MPU

1

, various means other than the integrated timer controller ITC may be used.

As can be understood from the description above, in the motor control system of the present invention, clock pulses output through a single channel of the processor are used in common by a plurality of motors, and accordingly, more motors than the number of the available channels of the timer controller can be controlled by the processor.

The motors which use in common clock pulses from a single channel may be either those to be driven at one time or those to be driven separately. Whether the motors which use in common clock pulses from a single channel are driven at one time or separately from each other can be controlled on the side of the processor. Further the motors can be driven either in the constant-voltage drive mode or the constant-current drive mode according to the type of the motors and the like.

In an image forming apparatus, a predetermined number of channels of the integrated timer controller ITC of the processor have been allotted to each function. Even if the number of motors to be controlled by the predetermined number of channels becomes larger than the predetermined number, all the motors can be controlled without an additional integrated timer controller ITC by use of the motor control system of the present invention. Since no additional integrated timer controller ITC is required, space for increased integrated timer controllers is unnecessary and increase in cost can be suppressed.