RORO ROOF CONTROLLER

INTRODUCTION

This note describes the design for a Roll-Off roof controller.

DESIGN CONSIDERATIONS

1.1 The controller supplies reversible polarity 12VDC power to the motor that opens and closes the roof.

1.2 The roof uses two pairs of microswitches to indicate when the roof is (a) totally closed and (b) totally open. The switches provide a short circuit to indicate these conditions. Two switches are used in parallel for each position to ensure reliability. An open command will attempt to open the roof unless these switches indicate it is already fully open. A close command will attempt to close the roof unless these switches indicate the roof is already fully closed.

1.3 The controller accepts a single line input to open or close the roof. +5 VDC will indicate the command to open the roof. 0 VDC will indicate the command to close the roof.

1.4 Roof closed is assumed to be the normal (majority) state of the roof, and all relays in the controller are de-energised in this state.

1.5 Relays (rather than solid-state logic) are used to provide reliability in a high current inductive switching environment.

1.6 The Pulse Width Modulator was taken from an old electric drill. This is used to vary the speed of the motor to give a smooth slow roll off and roll back. The trigger on the module is adjusted by means of a cable tie that is wrapped around the module and trigger. Under test it is pulled taut to give the desired motor speed.

1.7 A three position switch is used to give the control options of (1) Test, (2) Manual or (3) Automatic.
The Test position enables the roof to be moved in small increments when a push button is pressed. The direction is given by another two position switch. CAUTION: Note that in this mode, the limit switches at each end are inactive!
The Manual position will open or close the roof in this position with direction being given by a second two position switch. Movement in either case will be the full length of the roof movement with microswitches at either end causing the movement to cease (by removal of power to the motor.
The Automatic position is under control of an external computer. Movement direction is controlled by the external voltage. Movement will be terminated when the roof reaches the end of its travel and activates the appropriate microswitches. In this mode an active voltage from either a rain sensor or a cloud sensor will cause the roof to close.

SCHEMATIC DIAGRAM

I/O SPECIFICATIONS

Notes:

1 An inactive level (0V) on either SC or SO indicates that the roof is not fully closed (SC) or not fully open (SO). If both of these signals are inactive, it will normally indicate that the roof is in transition between states. If both these signals are inactive for an extended period of time this indicates a fault condition.

2 The CS command indicates a desire by the external agency asserting the active signal (+5V) to open the roof. This will be over-ridden (a) when the manual-automatic switch (SW1) is in the manual position, and/or (b) when the Observatory sensitive rain sensor has an indication that rain has been detected.

3 Note that the CS command must be held active (+5V) for the roof to remain open. When it drops to zero, the roof will close, unless the manual-automatic switch (SW1) is in the manual position AND SW2 is in the open position.

OPERATION

The normal state of the roof is closed. When this is the case, microswitches uSW1 and uSW2 will be closed turning on transistor Q1 and asserting output signal SC. This will turn off Q2 and relay RL1 will be de-energised. At the same time uSW3 and usw4 will be off, as will Q3 and RL2 will also be de-energised.

If the input command line CS is low (0V) and S1 is in the auto position, Q4 will be off and RL3 and RL4 will be de-energised. No voltage is applied to the motor and the roof remains closed.

If CS is asserted high (and kept high), RL3 is activated which applies power to the motor from the closed contacts of RL2 with a polarity determined by the contacts of RL4 which is also energised by the CS high command. Power will be applied to the motor until the roof is totally open when uSW3 and uSW4 will close, energising RL2 and opening its contacts.

When CS is taken low, RL3 is de-energised and power will again be applied to the motor via the contacts of RL1 which is energised because uSW1 and uSW2 are open. Because RL4 has also been de-energised, the polarity applied to the motor will be in the opposite direction, which will cause the motor to close the roof.

The motor will only be energised by an ‘open’ command (CS high) if the microswitches indicate that it is not already open, and it will only be energised by a close command (CS low) if the microswitches indicate that it is not already closed. Note that in the Automatic mode the roof will close if either the rain or the cloud sensors output an active signal.

If S1 is in the Manual position the CS command will have no affect and motor movement will be given by the direction switch S2. Note that the cloud and rain sensors are inactive in this mode.

If S1 is in the Test position, movement will occur when pushbutton S4 is held down. Direction in this mode is given by switch S3. This is the only mode in which small movements of the roof are possible. CAUTION: Note that in this mode, the limit switches at each end are inactive! This mode overrides the CS command and the rain and cloud sensors.