Simplified Drawing

The Grating Tilt #4 stage, though the movement is rotational, is considered a constrained, linear stage. This means that the motor moves the stage between forward and reverse limits. Electronically, this stage consist of the following components:

 

	1. DC servo motor with integral optical disc encoder
	2. Slotted optical switch that is used as the fiducial
	3. Forward and reverse primary limit switches
	4. Forward and reverse secondary limit switches

 

The motor/encoder is from Galil and is the same basic motor that has been used both in the ESI and HIRES instruments. The Galil part number is 50-1000. The motor is rated at 30 oz-in (0.21 Nm) of torque, 3750 rpm, and 1000 line encoder. The slotted switch is an OPB970T55 component from Optek (at one time TRW). The primary limits are SPDT switches from Microswitch #BZ-2RW822-A2 and the secondary limits are Microswitch #DT-2RV22-A7 DPDT switches. Note: the intervening connectors for the stage have been left off of the drawing for clarity. The complete schematic can be viewed by clicking the schematic button above.

The stage is driven by software commands sent to it's controller. The controller then uses software supplied parameters to generate an analog voltage in the range of -10V to +10V that goes to the power amplifier. The amplifier then drives the motor. The control loop is closed via the integral motor encoder.

Using this scheme, the control computer will issue a command such as PAC=1000 (Position Absolute axis C to encoder position 1000). The controller interprets the command and using preprogrammed acceleration, deceleration, and speed parameters, it determines the analog voltage output needed to move the motor to the correct position. This includes calculating the proper time to start decelerating the motor to come to a stop at the desired point. (There are many other set parameters burnt into the Galil controller such as feedback parameters, torque limits and the like). The derived analog output voltage is then applied to the power amplifier. The amplifier performs two functions. First, the amplifier provides an output current proportional to the input voltage. This is a conversion of one volt to one ampere. Second, it provides a pulse width modulated output to drive the motor. This signal is present whenever the AEN (Amplifier ENable) is asserted (TTL High). The AEN signal goes high when the SH (Servo Here) command is issued and goes low when either the MO (Motor Off) command is issued, or, if the OE (Off on Error) variable is set true, when the position error is greater then the error limit ER. The encoder supplies A and B phases in quadrature and thus is decoded to 4000 counts per revolution.

 

Simplified Drawing

 

This stage has the normal compliment of limits. These include, in order, the software limits, the primary limits and the secondary limits. The software limits are set to limit the range of motion of the stage to safe bounds. These limits have been determined empirically. To be enforced, the stage must be homed before initial use of the stage. The next set of limits a moving stage may encounter are the Primary Limits.

These are shown on the drawing as the FLSC ( Forward Limit Switch channel C) and the RLSC ( Reverse Limit Switch channel C). Their function is to stop the motion of the stage if they are activated. These are inputs to the motion controller that causes the controller to stop any further movement in that direction. It will, however, allow you to move back out of that limit. Notice that to get to these limits the stage has already violated the software limits. The secondary limits are there to prevent physical harm to the stage. These limits are DPDT switches that perform two functions. First, one pole of the switch is wired in series with one pole of the motor. When the switch is activated the power to the motor is cut off. THIS MEANS THAT THE STAGE MUST BE DRIVEN OUT OF THESE LIMITS BY HAND. At this point, the stage requires manual intervention for the safety of the stage. The second set of contacts are wired to supply a signal to the controller that the limit has been tripped. This signal is fed to the controller input IN2 on pin 40 of the amplifier terminal strip. Because the forward and reverse switches are wired in series, this input does not contain information as to which direction the stage was traveling, just that it is in a secondary limit. Again notice, to get to this limit both the software and primary limits have failed. Though the simplified drawing above does not show the stage interconnect box, the schematic does. It is important to note that the connectors to the interconnect box must all be plugged in to operate the stage. The limits are all wire via Normally Closed terminals on the switches. If a cable is disconnected the controller recognize the limit inputs as being active thus not allowing that stage to move.

1. Visual Inspection: Remove the appropriate hatch(es) to gain access to the TV camera stage. Looking into the stage check that the pink drive belt hasn't broken or come off of it's pulleys. Look into the limit switch area to determine that the switches and the wiring is intact. Check to see if the limit actuator is positioned within the limits. Finally, with the servo power off, check to see that the lens focus ring rotates freely by manually rotating the ring by moving the drive belt.

2. Cables: The first thing to look at is the cabling. Start at Galil controller panel #1 and check that it's stage cable is connected to J2. (As this stage does not use an auxiliary encoder, there should be no cable connected to J21). Next, look at the EL-1236 interconnect box cables. It is located at the front of the instrument on one of the supports for the front bulkhead. It is labeled TV Focus. (Note: the TV Focus interconnect box is also located in this area.) The main cable comes into the box from the rear part of the instrument and connects to JB1. The connectors leaving the box on the other side are JB2, JB3, and JB6. JB2 is the motor power cable. If it is disconnected the secondary limit signal will float high telling the controller that the stage is in the limit and also there will be no power to the motor. JB3 contains the connections for the primary limits and the fiducial. If it were unplugged you would get a primary limit error, again because with the cable off the controller sees the forward and reverse primary limits as being made (i.e. the input floats high.) The last cable is the ribbon cable that connect the motor encoder to the controller. If this cable was off the controller would try to move the stage. The motor would start to turn but the encoder would not change. Because the software sets the OE (Off on Error) the motor will turn off as soon as it has moved a small way. This is the result of the error in commanded position versus actual position has grown larger then the ER error value.

3. Power Supplies: The next logical place to check is the power supplies. The supplies in question are the 28V motor power, the 5V, +/-12V logic power, and finally the power supplies in the Galil controller. First, open the necessary covers on the electronics ring to gain access to Galil panel #1. The Logic Supply +5V can be measured across the +5 and GND terminal strips TBA and TBB. The +28V power supply can be measured across the two large large terminals on the Lambda power supply. The trickiest to measure is the Logic Supply +/-12V supplies. To get to the terminals of this supply the supply has to be removed from the Galil panel. To do this, remove the AC power cord that supplies the panel (the second power cord on the Panel plugs directly into the Galil controller and needn't be unplugged). Next, locate and remove the clear plastic AC shield that protects the AC input terminals of the logic supply. Remove the Allen head cap screws that attach the Logic Supply to the Opto-22 relay rack support. Now lay the supply out to where you can get to the +/-12V terminals with a meter and carefully plug the AC power back in. Measure between the +12V terminal and any GND terminal on TBB. Do the same for the -12V supply. On the Galil, extra connectors have been crimped onto the ribbon cables that connect the controller to the amplifiers. These connectors provide test points for all of the signals from the controller, including the internal power supply lines. To measure the Galil power supply insert probes into the following pins

4. Isolate the problem: Use a spare Galil 50/1000 motor to determine if the motor is being servoed. This can be done by connecting a spare motor by using the motor/limit test setup as shown below to the stage interconnect box.

 

Step 1: Stop dispatcher #1 and login to Galil controller #1:

1. log onto keamano as kics using the kics password for keamano.
2. Type: deimos stop dispatcher2.1
3. telnet to Galil #1: telnet 192.168.1.2 2005
4. Hit <return> a couple of times until you get the colon prompt :

Step 2: First, issue a MO (Motor Off) from the Galil command line. This will remove power from all motors if it is not already off. Disconnect the motor connector JB2 and the encoder connector JB6 from the stage interconnect box. Connect the Motor Test Connector's JB2 motor connector and JB6 encoder ribbon cable connectors. Now issue a SHB (Servo Here channel B) from the Galil command line. This should servo the motor and you should feel stiff resistance to rotating the shaft. If the motor runs away, remove motor power as above with the MO command, swap the red and black wires at the motor, and servo the motor again. Swapping the motor leads should ensure the motor runs the same direction as the encoder. If the motor runs away again the problem is likely that either 1) the EL-2260 Encoder Buffer has failed, 2) there is a problem in the Interconnect Box, or 3) there is a problem in the stage cable. If this is the case, next try inserting the spare EL-1236 Interconnect Box in place of the original and repeat the above test. If this test fails inspect the cable ends and pins for broken or bent pins. If the test motor servos but the stage motor doesn't, carefully check the wiring from the interconnect box to the motor. If the wiring looks OK, issue the MO command and reconnect the stage cables JB2 and JB6 to the interconnect box. Disconnect the red and black leads from the motor and connect them to the test motor. Issue the SHB command and again test the motor shaft for servo power.

Step 3: If the test motor servos OK test the Secondary limit switch by reading input bit 2 using: MG@IN[2] Change the state of the secondary limit test switch and retest. With the switch in the open position IN[2] should read back as a 1. With the switch closed it should read back as a 0. This will tell you that the secondary limit wiring to the controller is OK.

Step 4: If the above steps tell you that the motor and it's wiring are OK then install the Limit Test connector to test the primary limits and the fiducial input. First, set both test switches into the closed positions. Next, issue the command TSB (Tell Switches B axis). This will tell you the state of the primary limits.