Introduction:

The DEIMOS instrument rotation stage is run by a Linux PC with a Galil DMC-1920 Servo Motor Driver card installed. The PC talks to the instrument control computer over the private network. It also has a second network card that attaches it to the public network for diagnostic purposes. The rotation stage allows just over two full rotations, 790 degrees, of the barrel portion of the instrument. To make the two revolutions possible a chain and sprockets were added to the back of the instrument that run a puck/limit actuator back and forth from one side of the cradle to the other. The sprockets were sized to make the two revolutions of the barrel move the puck between the stage limit switches. An over-center limit switch was added at the middle of the travel of the puck to tell the PC which revolution the barrel is currently in. The limit switches used for end of travel of the stage consist of one over-center primary limit and one standard DPDT secondary limit switch. The over-center type primary limits allows the puck to toggle them and then continue on to actuate the secondary limits. Like other stages, the secondary limit switches cut power to the motor but, unlike other stages, there is a system to move the stage back out of a rotation limit. To do so, the operator must open the circuit breaker panel on the instrument and flip the Normal/Bypass switch to the bypass position. With this done, the instrument can be backed out of the limit by first, locating the puck to determine which limit is tripped, then push and hold the red button above that limit. This will rotate the instrument at a safe speed in the correction to disengage from the limit. As a side note, these buttons can also be used to check the balance of the instrument. To do so, one person should watch the current meter next to the Normal/Bypass switch while another person actuates the pushbuttons one at a time. When the instrument is in balance, the current draw should be about the same in both directions of rotation. After using the bypass system be sure to set the switch back to Normal.
For safety reasons, there are a number of other limit switches on the instrument that interact with the rotation. First, there are the 'Rotation Stop' buttons near each corner of the instrument and next to the drive motor. These are intended to act like a panic switch that anyone can push to stop the instrument rotation in an emergency. Once one of these buttons are pushed, the instrument will not be able to start rotating until the green 'Reset' button in C-Bay is depressed. To restore rotation, an operator must remove the cover to C-Bay and push the green 'Reset' pushbutton. Besides the 'Rotation Stop' limits, there are also the hatch limit switches. These are mounted at each of the opening hatches on the barrel of the instrument. They are: Dewar 1 Hatch, Dewar 2 Hatch, and the Man Hatch that allow entrance into the barrel, and the filter wheel, slitmask, and grating hatches that allow access to the changeable elements of the spectrograph. If any one or more of these hatches are open, an interlocking relay will stop or prevent rotation. Unlike the 'Rotation Stop' switches, however, rotation will be restored once the hatch is re-closed. The last limit switch in the current path of the rotation motor is the 'Band Clamp' limit switch. This switch is actuated by the band clamp which physically locks the drive disk of the barrel to the cradle. The limit switch keeps power from being applied when locked.
Because of the complexity of the rotation stage, a manual paddle has been provided to assist in operation and troubleshooting. The paddle has the ability to operate the stage and provide feedback to the operator as to the status of the stage. The paddle is used by first, selecting 'Manual' on the toggle switch and then selecting the desired function via the two paddlewheel switched and finally pushing the 'FWD' or 'REV' button to start movement. Also, when in 'Manual' mode various LED's are used to show the status of the stage. Above the 'FWD' and the 'REV' pushbuttons are red LED's that are illuminated when the stage is in the limit for that direction. If both of these LED's are blinking, that means that the stage has not been initialized. Between the 'FWD' and the 'REV' pushbuttons is a yellow LED that is lit when the stage is moving. There is also a line of LED's on the left side of the paddle. As marked, these LED's are lit when a limit condition occurs. The possible limits are, from top to bottom: 'Band Brake On', 'Panic Button Pushed' (Rotation Stop), 'ESTOP Active' (Observatory ESTOP), 'Rotation Bypassed', and 'Hatch Opened'. Again, any one of these limits will stop the instrument from rotating.
Various modes of rotation are available to the operator. The mode switch will let you move at a fast (switch setting 0) or slow (switch setting 1) jog speed where that barrel will rotate while the direction pushbutton is depressed. If the 'Position Switch' mode (switch setting 2) is selected the instrument will move to the discrete position selected by the 'Position' paddlewheel switch. With 'Next 90°' selected (switch setting 3) the instrument will rotate to the next 90° position when either the 'FWD' or 'REV' button is pushed. The direction of rotation will depend on which direction button is pushed. In the 'Sound' mode (switch setting 4), ????????? The 'Home' (switch setting 7) will, when selected and a direction button is pushed, start the homing sequence for the rotation stage. When homing, the direction button that button that is pushed is irrelevant, the computer will determine and use the correct rotation direction to home properly. For 'Mode' switch position 3, 'Posn. Sw.', the positioning modes are as follows:

 

Sheet 1:

Simplified drawing

 

Sheet 1 gives a block diagram of the the instrument rotation stage. At the left side of the drawing is the Galil controller and at the right side is the Galil 500/1000 servo motor. The intervening boxes show the various limit switches that combine to assure safe operation of the instrument rotation. Attached beneath the Galil controller block is the Opto-22 relay rack. With the exception of the primary and secondary limits, all conditions that can disallow rotation are monitored here. Shown as black lines at the bottom are the various signals that the Galil controller, and thus the PC, monitor to determine that it is safe to rotate the instrument.

The first three blocks from the left show the standard scheme for running a stage. However, because of the complexity of the motion and the sheer size of the rotating portion of the instrument, other safeties have been added to the

Summery-- For the motor to run, the signal path must be complete. Each block to the right of the 'Stage Interconnect Box' represent physical switches that must be 'made' in order for the circuit to be completed. The Normal/Bypassed switch allows operation from either the computer or the Bypass Control system. Note that the Bypass system only bypasses the Primary and Secondary limits - all other limits must be correct before the Bypass Control system will rotate the instrument.

Sheet 2:

Simplified drawing

 

 

As the page title says, this is a more detailed block diagram for the rotation stage. At this level, most of the cables and some of the connectors and terminal strips are called out. Also, notice that each block has a 'Bay' reference. These correspond to the bay markings on the instrument.
On the left side, the first first block details the Linux PC. The PC talks to the instrument control computer (keamano) via the private net. The PC has a Galil DMC-1820 motor control card installed which connects via a 100-pin to the AMP-1920 servo motor amplifier. Also, a block representing the 48V Lambda power supply is shown connecting to the amplifier via four wires.

Sheet 3:

Simplified drawing

 

 

 

Sheet 4:

Simplified drawing

 

 

 

Sheet 5:

Simplified drawing

 

 

 

Sheet 6:

Simplified drawing

Above is a representation of the Rotation Interlock Box. Also shown is the rotation Band Clamp. The Band Clamp is a long metal strap that is used to clamp the rotating barrel of the instrument to the cradle. When applied, the clamping pressure is great enough to keep the barrel moving even with the instrument being out of balance. In fact, we have had people climbing on the barrel

 

 

Sheet 7:

Simplified drawing

 

 

 

Sheet 8:

Simplified drawing

 

 

 

 

Simplified drawing

 

 

 

Sheet 9:

Simplified drawing

 

 

 

Sheet 10:

Simplified drawing

 

 

 

Sheet 11:

Simplified drawing

 

 

 

Sheet 12:

Simplified drawing