GB2463235A

GB2463235A - Controller for roller driver DC electric motor

Info

Publication number: GB2463235A
Application number: GB0816007A
Authority: GB
Inventors: Kam Sik Leung; Siu Chung Yip
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2008-09-03
Filing date: 2008-09-03
Publication date: 2010-03-10
Also published as: GB0816007D0

Abstract

A relay operated controller for a DC motor of a roller drive 18 used in a roller blind 10,14, projector screen and the like, short circuits the motor terminals when the motor is switched off to increase the motor holding torque. The controller 22 also provides a speed limiter to prevent the roller drive 13 operating too quickly in the rolling down mode which may occur as the weight of the material unwound from the roller causes the roller to self unload and back drive the motor.

Description

ELECTRIC MOTOR

FIELD OF THE INVENTION

This invention relates to an electric motor and in particular, to a roller drive for rolling and unrolling a flexible sheet such as a curtain roller, a screen roller and the like.

BACKGROUND OF THE INVENTION

Motor driven roller curtain or roller blind devices especially Holland' blinds have a motor driving a roller often through a gearbox. The weight of the blind or curtain which hangs of the roller has a significant effect on the motor performance due to the torque this weight applies to the motor drive. The heavier the material and the larger the diameter of the roller, the greater the torque produced. This has two major impacts on the motor drive performance. As the motor is winding up the blind from the fully unwound condition, the motor is starting under full load condition and is possibly struggling to wind up the blind against the weight of the material hanging off the roller. However, as the blind is being wound up the load on the motor is reducing until the roller is fully wound up, at which time the load is at a minimum, which also means that the motor is slowest when the blind is fully extended and fastest when almost fully wound, in the up direction. When lowering the blind, the motor starts off with very little load as the load of the blind is canied by the roller and is able to get up to speed very quickly. As the blind unwinds, the weight of the material assists the motor to unroll the blind and may get to the situation where the motor is unable to control the speed of the roller. This results in a large difference in speed between winding up and unwinding where the time taken to roll up the blind may be substantially greater than the time to unwind the blind.

Another problem is that the weight of the blind, combined with the diameter of the roller can produce a considerable torque on the roller drive mechanism and at the lower positions of the blind, the motor may not have enough holding force when turned off to hold the blind in the desired stopped position resulting in the totally unsatisfactory condition where the blind can not be positioned between, for example, 80% and 100% extended. In this example, when the blind is stopped at the 80% extended position, the weight of the unwound material will continue to unwind the roller when the motor is turned off, a condition known as back drive, where the motor is forced to rotate by the load. In effect, the load is driving the motor instead of the motor driving the load. This occurs because the torque produced by the weight of the material hanging from the roller is greater than the holding torque of the motor, even where the roller is driven by the motor through a gearbox.

These two problems are becoming more apparent as manufacturers try to use smaller and more efficient motors which have less magnetic holding force and which operate as a direct drive (no gearbox) or with very simple gearbox to reduce the power loss caused by the gearbox.

Prior art roller drive mechanisms traditionally use large motors operating through complex gear trains, use high speed motors coupled with high ratio gearboxes, or use complex anti-back drive clutches or mechanical braking systems attached to the motor or to the roller to hold the roller in the desired position. One proposal using an electronic controller maintains a holding current passing through the motor windings to increase the holding torque resulting in the motor being continually operated in a stall condition when the curtain is not being moved. All of these approaches add considerable complexity to the roller drive mechanism and are not conducive to efficient use of power and space.

One advantage of using a small motor is that the roller drive mechanism can be installed inside the roller itself, eliminating the external and often ugly motor and gearbox attachment adjacent the roller, giving more mounting options for the designer or architect.

SUMMARY OF THE INVENTION

Hence there is a desire for an improved controller for the motor of a roller drive mechanism for flexible material, such as curtains, blinds, screens and the like, which will enable the use of smaller, more efficient DC motors.

This is achieved in the present invention by a motor controller having an off state in which the motor terminals are electrically shorted together.

Accordingly, in one aspect thereof, the present invention provides a controller for a DC motor of a roller drive, comprising: a first relay having first and second contacts; a second relay having third and fourth contacts; an up switch for operating the motor in an up direction; a down switch for operating the motor in a down direction; a stop switch for stopping operation of the motor; wherein the motor has first and second motor terminals and in the stop condition the first and third contacts connect said motor terminals together.

Preferred and/or optional features are set forth in the dependent claims.

According to a second aspect, the present invention provides a roller drive mechanism including a DC motor and a motor controller as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view of a roller blind, used as an example to describe the invention; Figure 2 is a schematic wiring diagram of the prefened motor controller in the off mode; Figure 3 is a schematic wiring diagram view of the controller of Fig. 2 in the up mode; Figure 4 is a schematic wiring diagram view of the controller of Fig. 2 in the down mode, under light load; and Figure 5 is a schematic wiring diagram view of the controller of Fig. 2 in the down mode under heavy load.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 illustrates a roller blind 10 to which the invention is applicable. The roller blind comprises a roller 12 rotatably fixed to a structure such as a wall by roller mounts 16. Wound about the roller 12 and shown partially unwound is the material forming the blind 14. As such, the roller blind represents any roller based system having a flexible material which is wound and unwound from a roller, such as blinds, curtains and screens for projectors, privacy or decoration. To rotate the roller 12 to cause the blind 14 or other material to retract onto or extend from the roller, a drive mechanism is provided. The preferred drive mechanism is a motor 18, with or without a gearbox, located inside the roller 12, preferably inserted into one end of the roller and fixed to one of the roller mounts 16. Wires 20 to connect the motor to a control panel preferably pass through the same roller mount 16. A controller for operating the motor niay be fitted to the motor inside the roller where it is physically protected by the roller but most preferred is for the controller to be located remote from the roller in a conveniently located control panel 22, providing easy access for an operator. In this manner only two wires 20 need be connected between the motor 18 and the control panel 22.

Figure 2 illustrates the preferred circuit for the motor controller 24. The controller is shown in the idle of OFF' state. The controller is designed to control rotation of the roller 12 by controlling the motor 18 to move the blind up, down or to stop at a desired position. The circuit comprises two relays 26,28 which are controlled by three switches, an up switch 30, a down switch 32 and a stop switch 34. Each re'ay 26,28 has two change over contacts and is known as a double-pole, double-throw (DPDT) relay. Each switch is a momentary push button switch. The up and down switches 30,32 have normally open contacts and the stop switch 34 has normally closed contacts. Up and down motion is achieved by driving the motor in the desired direction by changing the polarity of the DC voltage applied to terminals 36,38 of the motor. In the stop mode, the motor terminals 36,38 are electrically shorted together.

The controller and motor operate on DC power and in Fig. 2, the positive rail 40 is shown at the top and the negative rail 42 is shown at the bottom of the diagram, connected to earth. The motor 18 has first and second motor terminals. The first motor terminal 36 is connected to the common terminal of a first contact 44, being the first contact of the first relay, the up relay 26, while the second motor terminal 38 is connected to the common terminal of a third contact 46, the first contact of the second relay, the down relay 28. In the idle or OFF state, both motor terminals 36,38 are connected to earth, or the negative supply rail 42 by the first and third contacts 44,46.

This produces a short circuit across the motor terminals and dramatically increases the holding torque of the motor, meaning that with the motor terminals connected together it is very difficult to physically rotate the shaft of the motor as the motor appears as a generator driving a very heavy load.

In the left of the diagram of Fig. 2, the up and down relays 26,28 are shown connected between the positive rail 40 and earth through various contacts and switches. The up relay 26 is connected on one side to the positive rail 40 through a fourth contact 50 being the second contact of the second relay 28 and the up switch 30. In parallel is a direct connection through a second contact 48 which is the second contact of the up relay 26. The down relay 28 is connected to the positive rail 40 by the second contact 48 and the down switch 32 and also by a parallel connection through the fourth contact 50. Both relays are connected to earth through the stop switch 34. A first diode 52 is placed in the connection between the down relay 28 and the stop switch 34 to prevent recirculating current from holding in the down relay. The first motor terminal 36 is directly connectable to the positive rail 40 by the first contact 44 when the up relay 26 is operated. The second motor terminal 38 is connected to the positive rail 40 by the third contact 46 via a voltage divider network comprising a first resistor 56 and a second resistor 58, a second diode 54 and the fourth contact 50, when the down relay 28 is operated.

In the OFF state, the motor terminals are short circuited together. The roller and blind are locked in position by the force of static magnetic friction, magnified by the gear ratio of the gearbox, if any. Should the blind tend to move down due to the weight of the unwound material or other reason, a regenerative force is created by induced EMF, in the up direction. This counter force will hold the blind in equilibrium without additional energy from the power supply.

Fig. 3 illustrates the circuit and current flow of the controller 24 in the UP' state.

When the up switch 30 is pressed, current flows through the fourth contact 50 and the up switch 30 to supply power to the up relay 26 which is connected to earth through the stop switch 34. This operates or changes the state of the first contact 44 and the second contact 46. The second contact 48, in the operated state, directly connects the up relay 26 to the positive rail 40 bypassing the up switch 30 and allowing the up relay 26 to remain active when the up switch 30 is released. The first contact 44 now connects the first motor terminal 36 to the positive rail 40 and current flows from the positive rail 40 through the first contact 44 to the first motor terminal 36, through the motor 18 to the second motor terminal 38, through the third contact 46 to earth (as indicated by the block arrows). Thus operating the motor in the up direction. The motor continues to be activated in the up direction until the stop button 34 is pressed, causing the up relay 26 to drop out and switching the controller 24 back to the OFF state. Should the down switch 32 be pressed when the up relay 26 is active, the down relay 28 is not activated as the second contact 46 in the active state isolates the down switch 32 from the positive rail 40, preventing simultaneous operation of the up relay and the down relay.

Fig. 4 illustrates the circuit and current flow of the controller 24 in the DOWN' state under light load. When the down switch 32 is pressed, current flows through the second contact 48 and the down switch 32 to supply power to the down relay 28 which is connected to earth through the stop switch 34. This operates the third contact 46 and the fourth contact 50. The fourth contact 50, in the operated state, directly connects the down relay 28 to the positive rail 40, bypassing the down switch 32 and allowing the down relay 28 to remain active when the down switch 32 is released. The third contact 46 now connects the second motor terminal 38 to the positive rail 40 via the first resistor 56 of the voliage divider network and current flows from the positive rail 40 through the third contact 48, through a second diode 54, through the first resistor 56, through the third contact 48 to the second motor terminal 38, through the motor 18 to the first motor terminal 36, through the first contact 44 to earth. Thus operating the motor in the down direction. The motor continues to be activated in the down direction until the stop button 34 is pressed, causing the down relay 28 to drop out and switching the controller 24 back to the OFF state. Should the up switch 30 be pressed when the down relay 28 is active, the up relay 26 is not activated as the fourth contact 50 in the active state isolates the up switch 30 from the positive rail 40, preventing simultaneous operation of the up and down relays. In this configuration, there is some current lost through the second resistor 58 of the voltage divider. However, the reduced current provided to the motor because of the voltage divider and in particular because of the inclusion of the first resistor 56 in the motor current supply circuit compensates for the lighter load in the down direction to more closely match the up and down speeds.

Fig. 5, illustrates the circuit and culTent flow of the controller 24 under heavy load.

Heavy load is defined as when the load on the roller is sufficient to cause the motor to be driven by the load or to over speed. The motor begins operating in the down mode as described above. When the load tries to back drive the motor, the motor 18 begins to behave as a generator. The circuit for the down relay 28 remains as before and the first and second diodes 52,54 prevent the motor current flow from dropping out the S down relay 28. As the voltage across the motor changes and the motor begins to operate as a generator, the current through the motor changes direction with the motor terminals 36,38 being connected together across the second resistor 58 which now operates the motor in a regenerative braking mode with the full output generated by the motor being applied across the second resistor 58 slowing down the speed of the motor under the increasing torque applied by the unwinding of the blind. When the stop switch 34 is pressed, the down relay 28 drops out deactivating the third contact 46 and placing a direct short across the motor terminals 36,38 (shorting the generator output), rapidly stopping the motor 18 and returning the controller to the OFF state.

The controller of the present invention allows the use of smaller, more efficient DC motors in a roller drive with improved holding torque. One advantage of using a small motor is that the roller drive mechanism can be installed inside the roller itself, eliminating the extema and often ug'y motor and gearbox attachment adjacent the roller, giving more mounting options for the designer or architect.

In the description and claims of the present application, each of the verbs "comprise", "include", "contain" and "have", and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.

Although the invention is described with reference to one or more prefened embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.

Claims

CLAIMS: 1. A controller for a DC motor of a roller drive, comprising: a first relay having first and second contacts; a second relay having third and fourth contacts; an up switch for operating the motor in an up direction; a down switch for operating the motor in a down direction; a stop switch for stopping operation of the motor; wherein the motor has first and second motor terminals and in the stop condition the first and third contacts connect said motor terminals.
2. A controller according to Claim 1, wherein the first and third contacts connect said motor terminals to earth.
3. A controller according to Claim 1, wherein when the up switch is operated the first relay operates the first contact to connect the first motor terminal to the positive power terminal.
4. A controller according to Claim 1, wherein when the second switch is operated second relay is operates the third contact to connect the second motor terminal to the positive power terminal.
5. A controller according to Claim 4, wherein the motor is driven in the down direction through a self regulating speed control circuit when the down switch is operated.
6. A controller according to Claim 5, wherein the second motor terminal is connected to the positive power supply through a voltage divider fed by a diode connected to the positive power supply by the fourth contact.
7. A controller according to any one of the preceding claims, wherein the first and second relays are connected to earth through the stop switch which is a normally closed push button switch.
8. A controller according to Claim 7, wherein the second relay is connected to earth via a diode.
9. A controller according to any one of Claims 3 to 5, wherein the first and second switches are normally open push button switches and when operated shorted out by the second contact or the fourth contact to maintain the first relay or the second relay in the operated state respectively until the stop switch is operated.
10. A controller according to Claim 9, wherein the second contact prevents the second relay from being operated when the first relay is in operation and the fourth contact prevents the first relay from being operated when the second relay is in operation.
11. A controller for a DC motor of a roller drive, substantially as herein before described with reference to the accompanying drawings.
12. A roller drive comprising: a roller, a DC motor, and a controller as defined in any one of the preceding c'aims.