Safe mode - is a subset of the auto mode that is entered either when the entrance door is opened or by software command. It is exited by either by software command or by pressing the reset button near the entrance door. Here are more details on safemode. Safemode will consiste of slower slew rates, but all other functions are the same.
Manual Mode - there really isn't a manual mode, you simply turn off the scheduler program and type commands to the observatory computer in real-time. If control is needed from inside the dome, an ethernet wired laptop will have to be used (unfortunately KPNO frowns on WiFi).
Maintenance Mode The MOP will not be dismantled. However, the EOS manual paddle will not be used. Instead there will be newly constructed, very simple manual paddle that can be installed by removing a jumper connector and connecting the paddle and running the desired axis manually. This mode is for experts only.
Axes: Hour angle, declination, secondary focus, guider X, Y, and Z, Shutter, Mirror Cover
Although the software will try to prevent the axes from striking a limit, when one has been struck the motor controller will cause the motor associated with that axis to stop and the program will issue an error. To move the axis off the limit simply make a new command to put the axis is a position in the opposite direction.
The normal limits are used to determine the end of motion. The limits cause the motor to stop moving in the active direction.
Axes: Hour angle, declination The failsafe limits lie outside of the normal limits and should not normally be struck. There will be two indications of the limit strike: 1) the panel light will be illuminated 2) the software will know the offending limit. When a limit is hit, the +56V power to the affected drive motor will be turned off preventing any motion. Finally the observatory will execute an emergency closedown (see below).
Something bad must have happened when the telescope hits the failsafe limits so expert manual intervention will be needed. To get the axis off the limit the override button that must be continuously held down by hand to reestablish power to the drive amplifier. Then the manual axis paddle connected to move the telescope out of trouble.
Axis: mirror cover
The actuators have built in failsafe range of motion limits. These are all wired in series. Similar to above, but the 24V mirror drive power will be disabled and the manual override process by an on-site expert is required.
Both the normal and failsafe tilt limits have all been wired in series and act as a failsafe and disable the hour angle and declination drive amplifiers. To recover requires manual intervention. This procedure is chosen because the tilt limits should never be tripped under normal operation and the determine the direction to get out of the limit may be subtle.
The emergency stop button will turn off the d.c. power to the following motors:
It will also stop and prevent:
Dome rotation Shutter motion Note: this is why the EStop is not weather safe.
Not affected by the EStop:
Great White Spot
There is also a solid state relay that controls the a.c. input to the power supplies. When shutting down the telescope for the night, this will be turned off by computer.
There is a solid state relay on the amplifier power supply d.c. output. This will be turned off in fault conditions by relays.
I don't really trust software lockouts for this purpose. Instead, I plan on the following.
The EStop button will disable the motion of almost everything. The trouble with it is that you can't move anything either. There will be maintenance paddles that will plug into the electronics and disable automatic control. These paddle should be used whenever remote or autonomous motion is unacceptable. The software will be aware that a paddle is plugged in, but it will be powerless to do remove it.
When done, the paddle is removed and replaced with a jumper to resume automatic operation.
There are four controls:
The PLD is programmed to do the following
The mirror has four leaves, there are two smaller leaves 1, and 3 and two larger leaves, 2 and 4. When opening the mirror the larger leaves have to be opened first, followed by the small leaves. When closing, the small leaves have to close first, followed by the large ones.
There are four limits on each of actuators: FS+, LIM+, FS-, LIM- . I have wired the Failsafe limits in series so if any of them fail, the power to the mirror cover is removed and the cannot move either open or close. Failsafe strikes mean something has failed and so expert manual intervention is needed.
Estop will have the same action as a FS overstrike. i.e. the ground the actuate the mirror drive relays is removed.
I have also wired the limits so that the leaf sequencing is done entirely by input from the limits.