Zone control method in roller conveyor and zone controller

• US 20010027909A1
• Filed: 03/30/2001
• Published: 10/11/2001
• Est. Priority Date: 04/06/2000
• Status: Active Grant

• Current Assignee: Itoh Electronics Incorporated
• Original Assignee: Itoh Electronics Incorporated
• Inventors: Itoh, Kazuo, Tachibana, Toshiyuki, Kujihashi, Yoshiyuki
• Granted Patent: US 6,459,224 B2
• Time in Patent Office: Days
• US Class Current: 198/788
• CPC Class Codes: B65G 13/075 Braking means
• CPC Class Codes: B65G 43/08 Control devices operated by article or material being fed, conveyed or discharged and controlling the discharging devices B65G47/42
• CPC Class Codes: B65G 47/261 Accumulating articles
• CPC Class Codes: B65G 47/31 by varying the relative speeds of the conveyors forming the series

Abstract

In a roller conveyor system for carrying out zone control, a conveyed article can be stopped in an approximately constant position without varying the position where the article is stopped in a desired control zone even if the weight of the article varies. In order to syop the article in a predetermined control zone, such stop control is carried out that a motor is decelerated and stopped in a plurality of braking systems depending on the change in the pulse width of a rotational pulse signal to stop the article with high precision in a predetermined stop position.

Claims

1. A zone control method in a roller conveyor which is divided into a plurality of control zones arranged in the direction of conveyance and has conveying drive rollers driven by a motor provided in the respective control zones, comprising the step of

controlling the stop of said motor when predetermined stop control start conditions are satisfied during the conveying operation of the conveying drive roller provided in the predetermined control zone,

the stop control switching a braking force of the motor depending on the rotational speed of the motor.

2. The method according to

claim 1

, wherein

the stop control comprises the steps of

subjecting the motor to relatively weak braking, and

subjecting the motor to relatively strong braking when the rotational speed of the motor is increased by a rotating force arising from the inertia of an article which is conveyed on the conveyor after the rotational speed of the motor is reduced once.

3. The method according to

claim 1

, wherein

the stop control comprises the steps of

braking the motor, and

operating the motor at low speed,

much time being assigned to the step of braking the motor when the rotational speed of the motor is relatively high, while being assigned to the step of operating the motor at low speed when the rotational speed of the motor is relatively low.

4. The method according to

claim 1

, wherein

the stop control comprises the steps of

subjecting the motor to relatively weak braking,

subjecting the motor to relatively strong braking when the rotational speed of the motor is increased by a rotating force arising from the inertia of an article which is conveyed on the conveyor after the rotational speed of the motor is reduced once, and

operating the motor at low speed,

much time being assigned to the step of braking the motor when the rotational speed of the motor is relatively high, while being assigned to the step of operating the motor at low speed when the rotational speed of the motor is relatively low.

5. The method according to

claim 2

, wherein

the weak braking is performed by subjecting the motor to short-circuit braking, and

the strong braking is performed by subjecting the motor to plugging.

6. The method according to

claim 1

, wherein

the motor is a blushless DC motor,

a pulse signal is generated from an output signal of a magnetic pole detector of the motor, and

the rotational speed of the motor is judged on the basis of the pulse signal.

7. The method according to

claim 6

, wherein

the operating state of the motor is updated for each of pulses composing the pulse signal during the stop control.

8. The method according to

claim 6

, wherein

the stop control is carried out until the pulse signal counts a predetermined number of pulses from the time when the stop control is started, and completely stops the motor by a short-circuit brake after the stop control is terminated.

9. The method according to

claim 8

, wherein

the motor is operated at low speed until the article is conveyed to a predetermined position in the direction of conveyance in a predetermined control zone where the stop control is carried out after the stop control is terminated, and is then completely stopped by the short-circuit brake.

10. The method according to

claim 8

, wherein

the predetermined number of pulses is larger than the number of pulses composing the pulse signal from the time when the short-circuit brake is started to the time when an article having a predetermined weight which is conveyed on the conveyor is completely stopped by the short-circuit brake.

11. The method according to

claim 1

, further comprising the step of

reversing the conveying drive roller, considering as a requirement the condition that the article is positioned beyond the predetermined position in the direction of conveyance in the predetermined control zone where the stop control is carried out.

12. The method according to

claim 1

, wherein

at least the fact that a state transition of a load presence signal indicating whether or not the article exists at the center in the direction of conveyance in the predetermined control zone where the stop control is carried out occurred is included as predetermined stop control start conditions.

13. A zone controller for a predetermined control zone of a roller conveyor line which is divided into a plurality of control zones arranged in the direction of conveyance, for carrying out driving and braking control of a DC motor for rotating a conveying drive roller provided in the predetermined control zone comprising

a control circuit;

a drive circuit for outputting a control current to said motor on the basis of a control signal from the control circuit;

a first detection signal input terminal for inputting a detection signal of a first sensor for detecting whether or not an article is conveyed to a first position in the direction of conveyance in said predetermined control zone; and

a magnetic pole position signal input terminal for inputting an output signal of a magnetic pole detector of said motor,

said control circuit comprising stop control means started, considering as a requirement the condition that a state transition of the detection signal of the first sensor occurs,

the stop control means generating said control signal such that a braking force of the motor is switched on the basis of a pulse signal generated from the output signal of the magnetic pole detector.

14. The zone controller according to

claim 13

, wherein

a conveyance signal and a forward/reverse signal are included as control signals supplied from the control circuit to the drive circuit,

the drive circuit outputs to the motor the control current for braking the motor by a short-circuit brake when the conveyance signal is off, while outputting to the motor the control current for driving the motor in a direction indicated by the forward/reverse signal when the conveyance signal is on, and

the stop control means comprises short-circuit brake signal generation means for turning the conveyance signal off, plugging signal generation means for turning the conveyance signal on and bringing the forward/reverse signal into a reversed state, the generation of the control signal by the plugging signal generation means preceding the generation of the control signal by the short-circuit brake signal generation means.

15. The zone controller according to

claim 13

, wherein

a conveyance signal and a conveying speed signal are included as control signals supplied from the control circuit to the drive circuit,

the drive circuit outputs to the motor the control current for braking the motor by a short-circuit brake when the conveyance signal is off, while outputting to the motor the control current for driving the motor at a rotational speed corresponding to the conveying speed signal when the conveyance signal is on, and

the stop control means comprises low speed switching means for switching said conveying speed signal to a low speed state when it is started, and short-circuit brake signal generation means for turning the conveyance signal on or off on the basis of the pulse waveform of the pulse signal.

16. The zone controller according to

claim 13

, wherein

a conveyance signal, a conveying speed signal, and a forward/reverse signal are included as control signals supplied from the control circuit to the drive circuit,

the drive circuit outputs to the motor the control current for braking the motor by a short-circuit brake when the conveyance signal is off, while driving the motor at a rotational speed corresponding to the conveying speed signal and outputting to the motor the control current for driving the motor in a direction indicated by the forward/reverse signal when the conveyance signal is on, and

the stop control means comprises low speed switching means for switching said conveying speed signal to a low speed state when it is started, short-circuit brake signal generation means for turning the conveyance signal on or off on the basis of the pulse waveform of the pulse signal, and plugging signal generation means for turning the conveyance signal on and bringing the forward/reverse signal into a reversed state, the generation of the control signal by the plugging signal generation means preceding the generation of the control signal by the short-circuit brake signal generation means.

17. The zone controller according to

claim 13

, wherein

the motor is a blushless DC motor, and

a signal representing the rotational speed of the motor is a pulse signal generated from an output of a Hall element of said motor.

18. The zone controller according to

claim 17

, wherein

the stop control means updates a control signal to be outputted to the drive circuit for each of pulses composing the pulse signal.

19. The zone controller according to

claim 17

, wherein

the stop control means generates a control signal for braking the motor by the short-circuit brake when the pulse signal counts a predetermined number of pulses from the time when it is started.

20. The zone controller according to

claim 19

, comprising

a second detection signal input terminal for inputting a detection signal of a second sensor for detecting whether or not the article is conveyed to a second position in the direction of conveyance in the predetermined control zone,

the second position being on the downstream side of the first position in the direction of conveyance,

the motor not being braked by the short-circuit brake until the detection signal which shows that the article is conveyed to the second position is outputted by the second sensor after the predetermined number of pulses is counted.

21. The zone controller according to

claim 19

, wherein

the predetermined number of pulses is set to a number larger than the number of pulses composing the pulse signal from the time when the short-circuit brake is started to the time when an article having a predetermined weight which is conveyed on the conveyor is completely stopped by the short-circuit brake.

22. The zone controller according to

claim 13

, further comprising

a third detection signal input terminal for inputting a detection signal of a third sensor for detecting whether or not the article is conveyed to a third position in the direction of conveyance in the predetermined control zone,

the third position being on the downstream side of the first position in the direction of conveyance,

the control circuit generating a control signal for reversing the motor, considering as a requirement the condition that the article is beyond the third position.

23. The zone controller according to

claim 13

, further comprising

an upstream connecting terminal to another zone controller on the upstream side,

a downstream connecting terminal to another zone controller on the downstream side, and

a connecting terminal to a host controller,

the upstream connecting terminal comprising at least an output terminal of the detection signal of the first sensor, and an input terminal of the detection signal of the first sensor in an upstream control zone,

the downstream connecting terminal comprising at least an output terminal of the detection signal of the first sensor, and an input terminal of the detection signal of the first sensor in a downstream control zone,

the control circuit comprising conveyance start signal generation means for generating a conveyance start signal from the detection signal of the first sensor and the detection signals of the first sensors in the upstream and downstream control zones, the conveyance of the conveying drive roller being started by the state transition of the conveyance start signal.