PFIS Filter Mechanism SPECIFICATION SALT-3130AE-00012 VERSION 1.0 16 February 2003 1. Scope 1.1 Identification This document covers the design of the Filter Mechanism for PFIS. In it are detailed the specifications, operating criteria and design. 1.2 System Overview The Filter Mechanism is the mechanism that selects one of 20 filters from the Filter Magazine and inserts it into the beam. 1.3 Document Overview This document first details the functional (science) requirements, then the technical (physical) requirements and then details the design of the mechanism and sub mechanisms. 1.4 Referenced Documents SALT-1000AS0007 SALT System Specification SALT-1000AA0030 SALT Safety Analysis SALT-3120AA0002 Grating and Filter Specification Document SALT-3170AE0005 PFIS Safety Analysis SALT-3140AE0015 Interlock Specification and Design Document SALT-3140AE0020 Actuators and Sensors SALT-3130AE0002 PFIS Mechanical Overview SALT-3130AE0003 PFIS Pneumatics Overview Document Doc No. SALT-3130AE-00012 1
2. Science Requirements 2.1 Schematic Diagram Magazine 20 Filters Optical Axis Camera Tube Dewar Filter In Position 2.2 Geometry 90mm 8mm Maximum Filter Size 130mm 2.3 Speed into Position and Duty Cycle Time to change filter ~20 seconds No. of angle changes per evening: ~20 Doc No. SALT-3130AE-00012 2
2.4 Positional Repeatability and Alignment X-Y placement: 60 microns repeatable 15 microns during observation (Z-placement has no discernable effect on image quality) Tip-tilt: 6.0 arcmin repeatable (150 micron end to end) 1.5 arcmin during observation (50 micron end to end) Note: X is short dimension, Y is long dimension, and Z is along the optic axis of the camera. 2.5 Operational Modes The mechanism must be able to select any of 20 filters and place it in the beam. The filter magazine invades the PFIS 3000mm diameter envelope for 5 filters while the camera is at the unarticulated position. The 5 inner-most filters in the magazine must thus be chosen to be the ones used at highest articulation angle. 3. Technical Requirements 3.1 Interfaces The filter mechanism is attached to the articulation frame structure along side the camera tube. The magazine must remain at least 152mm from the optical axis so as to be outside of the camera. The dewar envelope is smaller than the camera tube in diameter. The gap between the last camera element and the dewar field lens is 27mm and the filter and all it s in-situ mechanism need to be within this envelope. 3.2 Physical Characteristics 3.2.1 Mass Estimate The Mechanism currently has an estimated mass of 15.84kg (including filters). The current estimate breakdown is given in the parts list appendix. 3.2.2 Materials used and Properties Doc No. SALT-3130AE-00012 3
The baseline choice of material for this mechanism will be aluminium. The magnets mode from Alnico 5. The sliding surfaces on the aluminium magazine will be given a low friction coating. All surfaces will be black anodised. 3.3 Positional Tolerances The positional tolerance of the optical elements is detailed in section 3. The articulation mechanism will provide repeatable positioning of the camera to 15 microns. 3.4 Drive Requirements 3.4.1 Maximum Heat and Power Output The Power and temperature requirements of the SALT Telescope as set out in SALT System Specification Section, 5.3.2.5 shall be adhered to. 3.4.2 Encoding All motor driven stages will have absolute encoding while pneumatic actuators will only have position sensors at their end positions. The motor drive stage will have encoding and soft limits used for positioning while hard limit switches will stop the stage from going outside of its operating range. The articulation mechanism will have full range quadrature encoding with an accuracy of 15 microns. 3.5 Safety All mechanisms shall be designed such that electrical or software malfunctions cannot damage any hardware. Pneumatics should hold their position during a power failure and solenoids should fail in a clamped position Doc No. SALT-3130AE-00012 4
4. Description of Design 4.1 Layout 4.1.1 Basic Overall Layout Stationary Face Plate Magazine Camera Tube Stage Sliding Face Plate In Position Assembly The in position assembly is mounted to the camera tube flange. The Stage is mounted to the articulation mechanism structure and the magazine is fixed to the stage. Doc No. SALT-3130AE-00012 5
4.1.2 Filter Magazine Filter Rails Steel Strip for Magnet attachment Filter Sliding Face Plate Stop Back View Stationary Face Plate angle Mount Holes Removable section for access to filter engagement Doc No. SALT-3130AE-00012 6
4.1.3 Face Plates Sliding Channel Rail Magnets Front Stop Stationary Face Plate (mounted to camera tube) 4.1.4 Filter Insertion slot Back Stop Sliding Face Plate Since the magazine protrudes form the instrument envelope when accessing the furthest in filters, the face plate needs to move with the magazine so that it does not remain outside of the envelope. (this is all done so that we can get 5 extra filters into the magazine. we use the fact that when articulated the filter magazine is pulled back of the envelope) The sliding face plate is pushed out with the magazine and then returns (attached to it with a magnet). When the sliding face plate gets in far enough, it strikes the back stop and stays attached to that with a magnet. (this is since the face plate cannot slide across the filter insertion slot). Doc No. SALT-3130AE-00012 7
4.1.5 Stage Mount Bracket Vane Switch Stage Stepper Motor Position Transducer 4.1.6 In Position Assembly Rollers Flexure Mount Bar Code Reader Insertion Pneumatic Adjustable End Stop Doc No. SALT-3130AE-00012 8
4.2 Speed of Motion The pneumatic actuators will undergo their full range of motion in less than 4 seconds. The linear stage has a lead screw with 16 threads per inch. The maximum speed of the motor (directly coupled) is 2000 rev/min. Twice the full travel of the linear stage 300mm, would require 200 revolutions which would take 6 seconds, running the motor at 75% of top speed would still enable full motion in 9 sec. Stacked together the motions would take a maximum of 17 seconds. Allowing 3s for the encoding keeps us within the allowed 20s. Remove Filter from beam (4s) Insert Filter (4s) Select New Filter (9s) 4.3 Motion Control 4.3.1 Stage Motion to Align magazine for required filter Motion The stage motion is by means of a Stepper Motor (Oriental Motors PK266-03) driving a worm screw on a linear stage. Encoding There is a Linear Cable Transducer (UniMeasure LX-PA-10k) which gives full range absolute encoding. On the elevator are vane limit switches at the extents of travel. There is an at a station indicators which comprise two vane switches along side each other and 2 metal vaned strip with teeth at the station spacing. By off-setting vaned strips slightly we create a narrow band station indicator. The at a station indicator switch and the narrow at home switch will be achieved using two vane type hall sensors in an exclusive or arrangement to ensure narrow acceptable ranges. Doc No. SALT-3130AE-00012 9
4.3.2 Slide Mask between Magazine and Focus Motion Motion in and out of Beam from the magazine is by means of a pneumatic actuator (FESTO DSNU-20-250-PPV-A). The actuator is controlled by a micro-pneumatic valve. Encoding There are proximity sensors (SMEO-4-K-24-B) at the home and extended position of the actuator. 4.4 Control Interlocks For the normal modes of operation to be executed, the following conditions must be met: 4.4.1 Magazine to select an new filter The Pneumatic must be fully extended 4.4.2 To pull a filter into the beam (or return it to the magazine) The Magazine must be at a valid station 5. System Air, Power & Signal Requirements 5.1 Air 2 l/min at 6bar. This will be the maximum usage and is expected during and insertion or the mask from the carrier into to focus position. 5.2 Electrical Power Item Quantity Power Voltage Max Duty Cycle Nema 23 Stepper Motor 1 24 24/day, 8/hour Solenoid Valve for Pneu 1.55W 24 24/day, 8/hour 5.3 5.4 Logic Item Quantity Resolution Vane Switch 4 20µm Cable Position Transducer 1 0.1mm Proximity Sensor Reed switch, magnetically actuated 2 0.1mm Bar Code Reader 1 Doc No. SALT-3130AE-00012 10
Mechanism SubAssembly Part Name Quantity Part Number Man/COTS Manufacturer Material Unit Mass Total Mass Filter FilterAssembly Filter 20 O Optic 0.20 4 Filter FilterAssembly Filter Holder Magnet 40 5K241 C Group Arnold Alnico 5 0.01 0.2 Filter FilterAssembly FilterHolder 20 M Aluminium 0.03 0.6 Filter FilterAssembly FilterHolderRail 40 M Aluminium 0.03 1.28 Filter InPossitionAssembly Bar Code Scanner 1 MS-3 CCD C Microscan 0.09 0.085 Filter InPossitionAssembly Bracket Bump Stop 1 M Aluminium 0.00 0.003 Filter InPossitionAssembly CameraFlange 1 M Aluminium 1.40 1.396 Filter InPossitionAssembly InSlotPusher 1 M Aluminium 0.01 0.01 Filter InPossitionAssembly Pneumatic Cylinder 1 DSNU-20-250-PPV-A C FESTO 0.39 0.393 Filter InPossitionAssembly Proximity Sensor Mount 2 SMBR-20 C FESTO 0.00 0.002 Filter InPossitionAssembly Proximity Sensor SMEO 2 SMEO-4-K-LED-24-B C FESTO Plastic 0.01 0.01 Filter InPossitionAssembly RollerFlexureMount (Filter) 2 M Aluminium 0.03 0.066 Filter InPossitionAssembly Standoff Roller In Position 1 M Aluminium 0.00 0.003 Filter InPossitionAssembly Track Roller (Filter) 6 LFR 5201 KDD C INA Stainless Steel 0.01 0.06 Filter Magazine Alnico 5 Button Magnet 4 MC5688K51 C McMaster Alnico 5 0.01 0.04 Filter Magazine Alnico 5 Front Bracket 2 M Aluminium 0.01 0.01 Filter Magazine Alnico Front Magnet Stop 2 M Aluminium 0.01 0.01 Filter Magazine Alnico Magnet Stop 2 M Aluminium 0.01 0.01 Filter Magazine Alnico Magnet Stop Bracket 2 M Aluminium 0.01 0.01 Filter Magazine Filter Magnet Strip 2 M Aluminium 0.13 0.262234 Filter Magazine Magazine Filter Bottom 1 M Aluminium 0.30 0.3 Filter Magazine Magazine Filter Front 1 M Aluminium 0.12 0.12 Filter Magazine Magazine Filter Rear 1 M Aluminium 0.12 0.12 Filter Magazine Magazine Filter Slide Plate 1 M Aluminium 0.77 0.77 Filter Magazine Magazine Front Angle 1 M Aluminium 0.02 0.02 Filter Magazine Magazine Slide Angle 1 M Aluminium 0.03 0.034 Filter Magazine Sliding Channel Teflon Tape 4 C Teflon 0.00 0.004 Filter Magazine Sliding Plate Magnet Bracket 2 M Aluminium 0.01 0.01 Filter Magazine Sliding Plate Magnet Bracket 2 M Aluminium 0.01 0.01 Filter Magazine SlidingFacePlate 1 M Aluminium 0.17 0.17 Filter Magazine SlidingFacePlate Channel 2 M Aluminium 0.06 0.12 Filter Magazine Stationary Face Plate Mount 1 M Aluminium 0.04 0.036 Filter Magazine Stationary Magnet Stop Mount 2 M Aluminium 0.01 0.01 Filter Magazine StationaryFacePlate 1 M Aluminium 0.23 0.23 Filter Stage Cable Possition Transducer 1 LX-PA-15-10K C UniMeasure Thermoplastic 0.09 0.085 SALT-3130AE-00012 11
Filter Stage Linear Bearing 1 LPS-12-30 C* Servo Systems Steel 3.17 3.17 Filter Stage Magazine Mount (Filter) 1 M Aluminium 0.85 0.85 Filter Stage Nema 23 Stepper Motor 1 PK266-02 C Oriental Motors Steel 0.70 0.7 Filter Stage Stage Mount 1 M Aluminium 0.59 0.588 Filter Stage Vane Hall Switch 5 VN101503 C Cherry Plastic 0.01 0.025 Filter Stage Vane Hall Switch 4 VN101503 C Cherry Plastic 0.01 0.02 15.84223 SALT-3130AE-00012 12