STUDY SUMMARY - IPMU

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<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) Figure 3.10-6: Patrol Region of a single fiber positioner (top view). The two motors in each positioner have axes that are offset from one another, allowing the fiber tip to travel anywhere within the patrol region. Features have been included in the Cobra Positioning system to make integration and test more efficient. The Cobra Positioners are fabricated and assembled with tolerances that keep the patrol areas sufficiently parallel to the focal surface to eliminate all but one manual adjustment during assembly. Also, the positioners are divided up into separable modules to make integration, testing, and servicing easier. Each module has its own electronics module, making verification of mechanical and electrical function and performance possible early in the construction phase. These features are in line with the overall project strategy to allow early and complete testing of subsystems. The Cobra Electronics uses a distributed-driver approach. This approach facilitates maximum motor movement flexibility with minimum wiring. A block diagram of the approach is shown in Figure 3.10-7. The Positioner System key component is the Positioner Module. This Module consists of a unique addressable FPGA and a driver per motor in the module. The basic approach has three steps: 1. Motor drive information is created in the positioning computer from data generated by the Metrology System. This consists of the Unique Module ID, the motor number in the module, the duration of the motors operation, and the direction CW or CCW of the motor. 2. This information is transmitted through an optical Ethernet connection to the Ethernet Interface, which reconverts the Ethernet Data format back into data commands that are forwarded to the proper Positioner Module FPGA. 39
<strong>SUMMARY</strong> REPORT WIDE FIELD FIBER-FED OPTICAL MULTI-OBJECT SPECTROMETER (WFMOS) 3. The FPGA generates the signals that have the proper duration frequency and phasing to cause the motor to rotate properly. Figure 3.10-7: Positioner System Block Diagram Proper packaging design and techniques are necessary to make the 2.5-volt signals from the FPGA compatible with the 120-volt square wave out of the drivers. To accomplish the electronics packaging, chip on board (COB), automated assembly, and automated testing techniques will be utilized. Testing will be performed to ensure noise and cross-talk issues are addressed. Sufficient resources have been allocated to allow early testing (by Positioner PDR) and multiple design cycles to characterize the performance of the electronics and bring the design to maturity. Once assembled and verified, the Cobra modules are then integrated to the Cobra Optic Bench, which interfaces to a tilt/rotation test fixture via the Positioner Alignment System. When the entire bench is assembled and the electronic modules are daisy chained together, the bench is functionally validated. The deformations due to temperature and gravity are acceptance tested before the components are integrated and verified at higher levels of assembly. Integration of fibers into the modules can be done in parallel. The design and schedule allows for integration of the fibers through the center of the positioners; this is a configuration that has been tested and meets the throughput requirements. However, schedule and workforce can be recovered by routing the fibers externally to the positioner. Early testing will determine whether the throughput requirements are met. If the requirements are met, the integration approach can be simplified and accelerated. The WFMOS control system provides the positioner movement planning software (MPS) with the target and the current fiber locations—as measured by the WFMOS Metrology System—of the individual optical fibers, specified in the coordinate system of the WFMOS instrument measurement plane. The MPS computes the motor drive information and generates an output file consisting of the sequence of movements for the embedded controller software to 40
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STUDY SUMMARY - IPMU

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