HHT Focus Translation and Directions for Manual Movement 13 Jun 97 The focus translation mechanism for the HHT consists of two motors which moves a translation stage along two axes in the vertical plane that contains the optical axis of the telescope. The motors are stepping motors. One can command them to move a certain number of steps or one can command them to move at a certain rate. There are two sensors which indicate the current position of the stage in the two axes. These are used to indicate the starting position of the stage and to verify that the stage moved by the amount requested. The translation stage is used to move the subreflector in the elevation direction and toward or away from the dish. However, the axes along which each motor moves the stage are not in these directions but rather at 45 degrees to these directions. Motor #1 moves the subreflector either up and in or down and out (as judged when the antenna is pointed at the horizon). #2 moves it either down and in or up and out. So to move the antenna only out (away from the antenna), for example, both motors must be moved by the same amount in the directions that move out so that their up and down motions cancel each other. Moving motor #1 by a positive number of steps moves the stage up and in but DECREASES the reading of the #1 position sensor. Moving motor #2 by a positive number of steps moves it down and in and INCREASES the reading of the #2 position sensor. Each step corresponds to a translation of 0.1 micron and each unit of the position sensor corresponds to 1.32 microns, thus there are 13.2 steps per position unit. Motor #1 has an 18 turn range of travel (0.9 inch) while motor #2 has a 16.25 turn range (0.8 inch). The position sensor for motor #1 doesn't have quite enough range. It saturates about 230 units (300 microns) from the stop at the low end and at 340 units (450 microns) from the high end. The range of the position sensors as read by CAMAC are 49152 to 65535 units. Motor #1 has a backlash of 350-450 steps (35-45 microns) and #2 of 90-180 steps (9-18 microns). The focus translation may be checked and moved manually with a program, TRYFOCUS. This program can send commands to the translation port, receive responses, and display the current positions. Manual focus commands should be sent with FAHREN stopped so that commands sent by FAHREN won't undo commands sent by TRYFOCUS and so that FAHREN won't intercept responses from the translation controller intended for TRYFOCUS. However, if one wants to use the SDH display to monitor the focus position in the elevation and axial directions (as apposed to the position along axes #1 and #2 printed by TRYFOCUS), FAHREN must be running. If this is the case, one should be sure that the FOCUS button is released so FAHREN won't send any commands. When finished with TRYFOCUS, enabling the FOCUS button will cause FAHREN to undo the absolute position mode normally used for manual control with TRYFOCUS. (FAHREN controls the focus by commanding a focus rate not a position; see MC command below.) To run TRYFOCUS, find an SMTSYS window running on Kronen, and type SOMEPRIV TRYFOCUS TRYFOCUS will type Command> to prompt for a Focus command. After each command line is processed (even if it is simply a key, the current coordinates of the stage in each axis (#1 and #2) is printed in encoder units (1 unit equals 1.3 microns). Each position is first printed in decimal followed by the same number in hexadecimal in parentheses. For example, #1: 59791 (E98F), Status = 1, Q-response, X-response, No Timeout #2: 57623 (E117), Status = 1, Q-response, X-response, No Timeout says that the stage is at position 59791 along axis #1 and at 57623 along axis #2. (The mid-point along each asis is approximately 57300.) The Status et al should always be as above. Focus commands consist of an axis number (1 or 2), the name of the command, and a parameter (if any). Commands must be typed in uppercase and *no* blanks should be used. (No error messages are typed. Unrecognized commands are simply ignored.) To prepare for manual operation, specify the velocity and acceleration to be used, specify absolute (vs incremental) positions, and put the controller in position (vs continuous motion) mode. For each axis, type: nV1 nA1 nMPA nMN substituting first 1 then 2 for the axis number, n. To check the current position of a motor, type nPR where n is the desired axis number, 1 or 2. The motor position will be printed in steps (1 step = 0.1 micron). Step = 0 can be anywhere. It is simply the position of the motor upon power up. To define the current position of motor n to be Step = 0, type nPZ (This does NOT move the motor.) To move motor n to position pppp, type nDpppp nG where pppp is the position desired. pppp may be any number of decimal digits and may be preceeded by a minus sign. The D command defines the goal and the G command causes the motor to move. Should a limit switch be encountered, the motor will stop before the goal is reached. To check the state of the limit switches, type nRA A response of *@ indicates no limit switch is tripped. If a limit switch is tripped, the @ in the response changes to a letter depending upon which limit switch is tripped. Other commands more useful in the rate mode (as opposed to the position mode), are: nR responds with *R if ready for a command, *B if busy moving the motor. nS stops the motor gracefully (at the deceleration rate specified with the A command). nK causes a panic (immediate) stop. For diagnostics, the incremental mode may be useful: nMPI This changes the D command to mean pppp steps from the current position. Then one can simply issue G commands to move by the specified amount without having to respecify the D command each time. The sign of pppp in the D command may be changed by nHs where s is either + or -. + means CW (increasing step number) and - means CCW. FAHREN uses the continuous move mode. This is selected by nMC and canceled by nMN MC causes no movement of the motor itself, but when it is in effect, the G command will cause the selected motor to move at the rate specified by the V command until an S or K command is received. In this mode, the value specified by the D command is ignored, however sign of the value is used to determine the direction of motion: - means CCW (decreasing step number) and + means CW. If an H command was specified after the last D command, the sign specified by H takes effect.