Mirror Positioning Control System with TwinCATand EPICS

Jihye SongUniversity of Pusan, ssongjihye@gmail.com

For monitoring and control of complicated detector system in large scale experiments,CBM (Compressed Baryonic Matter) at GSI is now designing the detector controlsystem using the EPICS (Experimental Physics and Industrial Control System). ForCBM RICH (Ring Imaging CHerenkov) prototype experiment the mirror positioningcontrol system with EPICS and TwinCAT program (The Window Control AutomationTechnology) has been programmed.

1 Introduction

1.1 Ring Imaging CHerenkov Detector

Fig. 1: CBM at FAIR, GSI

The CBM experiment will be a fixed tar-get experiment being operated at FAIR in GSI.(Figure 1) It is designed for the research ofquark matter under extreme conditions. Mainpurpose of the CBM experiment is investigat-ing the properties of super-dense nuclear matterand measuring rare and penetrating probes suchas dilepton pairs. Dileptons provide the key tovector-meson measurement in hot and/or densemedium. The measurement of electrons will beperformed with a RICH detector for momentabelow 8-10 GeV/c. The RICH detector is widelyused for identifying particles, which fly througha specific medium with a speed higher than thespeed of light in the medium (c/n, n : refractiveindex), and produce the Cherenkov radiation.

The principal components of the RICHdetector are the vessel containing Cherenkovradiator, a concave reflector and photo detec-tors at the focal plane of the reflector. Oneof the great advantages of this Ring Imagingtechnique is, that you can easily change themeasurable particle momentum range withchanging the Cherenkov radiator with variousrefractive index.

1.2 Purpose of Project

Fig. 2: RICH prototype in Giessen University

The CBM-RICH group in Giessen University,is responsible to develop the RICH detector usedat the CBM experiment for FAIR (Facility ofAntiproton and Ion Research) in GSI. Figure2 shows a draft of the prototype which is madeby Giessen University. According to the require-ments of the CBM-RICH experiment, it is neces-sary to check the uniformity of the 16 MAPMTs(Multi-Anode Photo Multiplier Tube) mountedon the prototype. It was designed for a frame

1

2 3 Mirror Positioning Control System

where 4 mirrors are mounted as concave reflec-tor, which is able to move on the vertical andhorizontal direction as a part of the prototype.

Fig. 3: Frame in RICH vessel

Fig. 4: degree and expected ring image

The mirrors are mounted on two frames asshown in Figure 3. These allow to move themirror in the vertical direction using the in-ner frame and in the horizontal direction withthe outer frame. The size of each MAPMT is52×52mm2, the gap size between the MAPMTsis 2mm. Four MAPMTs are needed to cover aring image. Since it is necessary to move thering image, like on Figure 4, one step movementof ±2◦ is needed on each axis. Two servo motorsare responsible for the system movement. One ismounted on top of the frame which allows in thehorizontal direction ±2◦ and 90◦, the other oneis located on left side of the frame which allowsthe movement in the vertical direction ±2◦.

2 Hardware for Control system

The whole scheme of the hardware componentsis shown in Figure 6. The mirror frame will beconnected to two servo motors (AM3021-0C41-0000) which are exclusively intended for speed-and/or torque-controlled operation via digital

Fig. 5: Frame for 4 mirrors

Fig. 6: Hardware : IPC, Servo Drive, Servo Mo-tors.

servo drives from Beckhoff. Each motor havea gear head for slow rotation to prevent break-ing mirrors. The servo motors are connectedto servo drive (AX5203-0000) with two cables,one is for power supply and the other one isfor encorder. For control system is an Indus-trial PC (C6915-0000) used. It is connected toservo drive and communicate by EtherCAT asethernet system. The TwinCAT program wasinstalled in this IPC based on window CE oper-ating system. Finally the TwinCAT program inIPC will be linked with EPICS on linux machinevia Modbus/TCP protocol.

3 Mirror Positioning ControlSystem

3.1 TwinCAT

The TwinCAT (The Window Control Automa-tion Technology) consists of the TwinCATSystem Manager and the TwinCAT PLC con-trol. TwinCAT System Manager is the centralconfiguration tool. It is where the inputs andoutputs of the software tasks and the physicalinputs and outputs of the connected fieldbussesare managed.[1] The main screen of TwinCAT

3.1 TwinCAT 3

Fig. 7: TwinCAT System manager

system manager is shown in Figure 7. Thereare 3 parts.

1. I/O-Configuration: Hardware componentsof the system.

2. NC-Configuration: Axis configuration.

3. PLC-Configuration: Control software.

I/O-Configuration communicates with hard-ware and these inputs, outputs are linked toNC(Numerical Control) - Configuration. TheNC allows to make the first operation of thesystem. Finally, the Input and output in NC- Configuration are linked to PLC - Configura-tion.

Fig. 8: TwinCAT PLC control

The TwinCAT PLC control is shown in Fig-ure 8. There are code and function blocks formirror positioning control. In Table 2 are thevariables used in the program. TwinCAT PLCcontrol provides also a local GUI (Graphic UserInterface) and in Figure 9 the GUI for mirrorpositioning control system is shown. Each vari-ables described in Table 2 are linked to a graph-ical element, so that it is easy to control the

Tab. 1: Address rule

Prefix DescriptionI InputQ OutputM Memory locationX Single bitB Byte (8 Bit)W Word (16 Bit)D Double word (32 Bit)

Tab. 2: Variables

Name Type meaning addressStart1 BOOL start MX0Start2 BOOL start MX1Stop1 BOOL stop MX2Stop2 BOOL stop MX3

A BOOL position (-2 , +2 ) MX8B BOOL position (0 , +2 ) MX9C BOOL position (+2 , +2) MX10D BOOL position (-2 , 0 ) MX11E BOOL position (+2 , 0 ) MX12F BOOL position (-2 , -2 ) MX13G BOOL position (0 , -2) MX14H BOOL position (+2 , -2) MX15

Zero BOOL position (0 , 0 ) MX4Tilt BOOL position (+90 , 0) MX5

NoTilt BOOL position (0 , 0) MX6NCcontrol BOOL NC enable MX7

rActualPosition1 LREAL real position MD400rActualPosition2 LREAL real position MD410

SetPosition1 LREAL Set value MD500SetPosition2 LREAL Set value MD510

mirror position on this control panel. There aretwo start buttons and stop buttons to controlthe power supply for motors, sixteen squaresrepresent each MAPMT and 9 circles show theposition of the ring image. Pushing the circle ofthe wanted position, mirrors will be moved andfinally it is able to see the ring image at the po-sition. In this control system, it is not allowedto activated more than one button at the sametime. On the right side of Figure 9 there are thefeedback of real position and for numerical con-trol. In case of numerical control, numerical padappears which allows to set any position. Theprogram is developed using a modulo functionto prevent that mirrors move 360 degree.

4 References

Fig. 9: TwinCAT PLC control Graphic User Inter-face

3.2 EPICS

As a SCADA (stands for Supervisory Con-trol and Data Acquisition) system, EPICSis a set of Open Source software tools, li-braries and applications, developed collabo-ratively and used worldwide to create dis-tributed soft real-time control systems for scien-tific instruments.[3] Figure 10 shows EPICS ar-chitecture. The IPC communicates to IOC (In-put Output Controller) via modbus TCP. TheIOC as EPICS server provides information andservice. A EPICS Client accesses the service orasks for information via channel access proto-col. CSS(Control System Studio) is one of theEPICS client tools for GUI as shown in Figure11. Every graphical element has a functionalitysame as in TwinCAT control panel.

Fig. 10: EPICS architecture

4 Summary & Outlook

In order to control positioning of mirrorsin RICH prototype, online control system isneeded. It is programmed with TwinCAT andEPICS. This online control system is success-fully installed and tested with servo motors. Itwill be used in experiment which will be doneat CERN in Oct.

Fig. 11: Control panel with CSS

Acknowledgments

This summer school project would never beenpossible without the guidance and support ofmy tutors and I have learned a lot through thisproject. I am very thankful to my advisors, Pe-ter Zumbruch, Burkhard Kolb and Tanya Tor-res De Heidenreich. I also greatly appreciatethe organizer, Joern Knoll. And I would liketo thank all the students for their friendship,support. If I have one more chance to take asummer school project, I would participate inprogram, of course.

References

[1] http://infosys.beckhoff.com/index en.htm

[2] http://beckhoff.com

[3] http://www.aps.anl.gov/epics/index.php

[4] http://cars9.uchicago.edu/software/epics/modbus.html

[5] http://cs-studio.sourceforge.net/