Barrel Stage Wiring

The barrel stage wiring section of this manual contains descriptions of the individual stage wiring for the barrel portion of the DEIMOS Spectrograph. It corresponds to the Barrel Stage Wiring tab in the electronics schematics binder.

Grating Clamp Stage, EL-3082

Schematic: schematics/GRATCLMP.sch.pdf
Page last updated: October 29, 2003

Sheet1:


Simplified Drawing

Some terms:
In the following discussion I will be using the following terms.

  1. Grating: the actual glass with the rulings on it.
  2. Grating Cell: the metal that hold the grating - what's being called the grating cell is actually any one of the grating tilt mechanisms. In this case its easier just to think of it as just a cell because we are not concerned with its tilting axis.
  3. Grating box: the stiff structure to which the grating cell is clamped.
  4. Grating Pin: a pin that is depressed when a grating cell is clamped into position. When depressed, it actuates a hall-effect sensor.
  5. PRM: the Primary Reference Mark that is used to define the position of the grating cell along the grating translation axis. This is an optical slotted switch.

Drawing Description:
The above drawing shows a block diagram for the grating clamp stage. The grating clamp stage is, in fact, different then the grating tilt stages. The purpose of the grating clamp stage is to clamp the selectable grating cells into the grating box. The grating box is the stiff structure that positions the grating cell in the beam. The grating clamps then are applied to hold the cell to the grating box. The cyan box on the left side of the diagram denotes Galil controller #2. The controller commands the grating slide mechanism to move the various cells into position for clamping. The lower portion of the Galil block shows the Opto-22 I/O functions. (Sheet 2 gives more details for the I/O) To the right of the Galil block is the stage interconnect box (in violet). This is a standard interconnect box that provides terminal strips for probing signals and a mount for the EL-2260 encoder buffer board. To the right of this block is a pink block that represents the interlock box for the grating slide stage limits. The magenta block in the lower, center of the diagram represents the set of 4 pneumatic cylinder clamps. The bright green block represents a box that acts as a limit switch mixer. The mixer brings together many of the various limit signals to send back to the controller. The light green box in the lower right corner represents the Primary Reference Mark for the grating clamping position. The other boxes represent the normal motor, primary limits, secondary limits, and fiducial for the grating translation stage. These are all discussed in the EL-3066 write up.

Overview of operation:
The overall operation of the grating translation stage and grating clamp stages works as follows. Assume that a grating cell is in position and the observer wants to change to a different grating. The order in which the new grating is moved into position is:

  1. The Galil controller will first retract (unclamp) the four pneumatic clamps.
  2. The controller will rotate the cell that is currently in position to a safe position. This ensures that there will be no mechanical interferences when the translation stage is moved.
  3. If all of the clamp retracted limit switches read correctly and all of the normal stage limits read correctly, the desired grating cell will be moved into position for clamping. The PRM (Primary Reference Mark) is used to determine that the new cell is positioned correctly in the grating box structure.
  4. The controller will now clamp the cell into place following a predetermined sequence of clamping and unclamping the various pneumatic clamps. The sequence was determined at Lick and is used to insure that the cell is in the correct place and clamped without any extra stresses on the cell. Also, the controller reads the condition of the grating pin limit to ensure that the grating has clamped sucessfully. This is a hall-effect sensor that is actuated by a pin that is depressed by the pressure of clamping the grating cell onto the grating box.
  5. The new grating is now ready to be used.

Detailed descriptions:
In the diagram above, the white insets display the critical functions for stage operation. Starting with the Galil controller block on the left side of the sheet, before any move will be attempted in software, all of the grating translation stage limits must be in the no limit condition. Further, before a movement will be attempted, all four of the grating clamps must be in the retracted position. If any of these conditions are not met, the controller will generate an error that will be sent back to the control computer. At this same time, the controller will turn on the PRM. The PRM is mounted on the non-moving portion of the grating box and interacts with a blade attached to each of the grating cells.
The Grating Clamp Interlock block on the drawing represents a series of four Crydom solid-state relays that are wired in series with one side of the motor power. If any one of the grating clamps is not retracted the relay will open and cause the motor to stop. As implied, each of the relays is accuated by a limit switch that senses that the pneumatic clamp is in the fully released position. The Grating Pin is a seperate hall-effect limit switch that works in concert with the grating clamp limits by sensing that the grating cell is clamped correctly into the grating box.
The Stage Limit Distribution Box is a metal box that is attached to the stage interconnect box. It's purpose is to collect many of the various limit input and

 

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Simplified Drawing