Motion Control Applications

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Revision as of 10:10, 20 April 2011 by Hovanes (Talk | contribs) (Tagger Dump Harp)

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Motor Applications Introduction


Scope

We need to plan for the following motor-based applications:

  • Goniometer (5 axis)
  • Tagger harp (1 axis)
  • Tagger dump harp (1 axis)
  • Tagger microscope (4 axis)
  • Collimator table (1 axis)
  • Converter/photon harp (1 axis)
  • TAC (1 axis) ?
  • Gamma profiler (1 axis) ?

This means 10 axes in tagger hall, 4 axes in Hall D. We can consider the three options shown below.


VME based

  • This approach would require two VME crate with a controller in each (one in tagger hall and one in Hall D) and OMS motor driver cards. This is a common way of doing it at Jefferson Lab.
  • Currently we are trying to avoid VME based systems, but harp applications need to have a VME scaler module. Therefore, for harp systems this would be a convenient way of doing it since the motor and the scaler module can be easily synchronized through a single VME bus.
  • The hardware cost can be high ~ $26K for the two VME crates (2x$6000), CPUs (2x$3400 each) and the 4 OMS VS4-040 cards (4x$1800).
  • Software from other halls and accelerator division can be used saving us on labor cost.



PLC based

  • PLC may be the cheapest way of doing it from point of view of hardware. For 18 axes of motion we probably will need about $17K; $14K for 9 AMCI 3202 modules for 1756, and approximately $3K for two 1756 chassis with communication modules.
  • I have not been able to find a true Allen-Bradley stepper motor drive card for ControlLogix PLC, AMCI was the only one I could Google. Allen-Bradley has expensive and sophisticated system for ControLogix.
  • We will need to develop the software nearly from scratch. This option also creates the usual extra layer of PLC/EPICS communications.
  • Implementing harp scans can be problematic because of the synchronization issue between the scalers and the motor read-backs. The bandwidth limitations of the EtherIP EPICS interface may cause problems in harp scan applications.


Newport XPS based

  • A new module for controlling multiple motor drivers from Newport with Newport XPS-DRV00 pass-through cards can be used.
  • This approached apparently is not used in JLab.
  • Mark Rivers uses these devices at APS and he developed EPICS support for this. In fact his SNL applications is probably directly usable for us, so little software development would be needed for this. He is using the pulse output from XPS to strobe the scaler module, and keeps the positions of the motors (encoders) in XPS to later synchronize with the scaler FIFO values. This is exactly what we are looking for.
  • Mark Rivers is working on changing this application to work without state code, and some of the general features of his current and future implementation are briefly described in an e-mail exchange.
  • The low-power motors can be controlled using XPS-DRV01 card, which is more expensive that pass-through cards, $571. But this would allow us to skip building of the driver box for applications like microscope counter and LED positioning.
  • This is an expensive option. The price for 3 XPS-C6 units fully equipped with six XPS-DRV00 cards would cost us $23K.
  • Software development cost is probably going to be low since we can nearly copy APS' application.


Goniometer Application

No plans now


Tagger Harp

Tagger harp mechanical hardware exists within the accelerator group's scope. They will installed the vacuum system and the motor, but we probably will have to instrument the harp stick and decide what readout we will need. In order to achieve 10^{{4}} dynamic range we need to instrument it with PMT-based readout, which accelerator division usually does not do. It is also not defined who will be responsible for the control software, but it would be logical if we use our readout method then we also build the controls for this harp.

The tagger harp will consist of a pair of thin wires (we can use more than one pair with different thicknesses), for instance 25μm iron wire, which will be positioned at 450 with respect to the stick and 900 with respect to each other. One of these wires would measure the x-profile of the beam, the other one the y-profile of the beam. The overall scanning range is expected to be on the order of 6cm.

The motor will be moving at a slow speed of ~0.5 mm/sec, resulting in a full scan lasting about 2-3 minutes. While the motors is moving we will need to strobe a scaler module either internally or externally to measure the number of hits in three PMT-based detectors mounted near the electron beam dump versus the displacement of the stick. The measured numbers are recorded on the disc and analyzed after the full scan is complete. If we use VME-based application then the motor controlling board and the SIS3820 or the JLab new discriminator/scaler modules are on the same bus, therefore synchronizing the reading of the two devices is easy. This setup exists and works very well in Hall B. If the scaler and the motor controlling card are not on the same bus then there is an issue of synchronizing the motor position and scaler readings over the network. One of the possibilities is to use the XPS module from Newport which can output 200 ns pulses on traveling equal interval (this intervals are either in space or time, the manual says they can be both, while Mark Rivers claims they can be only in time). The output pulses (there is such a trigger output per axis controlled by XPS) can be used to strobe the scaler advancing it to the next buffer element, while the XPS device records the position of the motor at that point in time. When the scan is over both the scaler buffer and the XPS buffer are read from EPICS. The FIFO length in the SIS3820 scaler can hold well over 10K readings even if all channels are used, and it can be increased by installing more memory. The XPS buffer is not limited for any practical purposes. We will only need about 10000 readings per scan, so the XPS+SIS3820 setup should work as well. The XSP module has EPICS support and a similar application was used at APS and is available for download, which could be a good starting point for us.

The analyzing software should be able to recognize the two peaks in the enhancements in the data and fit them to obtain the centroids x and y and their resolutions σx and σy. The analyzing software exists and can in principle be copied from the accelerator division or other halls. The scanning software may have to be rewritten based on what hardware we choose for this application.



Tagger Dump Harp

The main purpose of this harp is to monitor/measure electron beam energy by measuring the position and the profile of the electron beam after the tagger dipole magnet. The measurement should be done without any radiator in the beam-line. The full width of the beam in the x-direction will be between on the order of 1 mm while in y-direction the width of the beam will be similar to what it was at the radiator. The required precision of the measurement of the peak position to achieve 2 MeV resolution is about 800 μm. The harp will be located about two or three meters upstream of the first labyrinth wall while the detectors will be located close to the labyrinth wall.

Tagger Microscope

No plans yet


Collimator table

No plans yet


Converter/photon harp

No plans yet


Gamma profiler

No plans yet


Total Absorption Counter

No plans yet