TwinCAT PC-based Automation Technology for R&D Applications

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TwinCAT PC-based Automation Technology for R&D Applications

TwinCAT PC-based Automation Technology for

R&D Applications

Ramdas Chandrashekar,

Training and Academic Segment Manager BECKHOFF Automation Pvt. Ltd., India

AbstractThe TwinCAT technology and other products developed by BECKHOFF Automation GmbH have been used by many R&D product development companies worldwide in enabling Automation of their products. The products span domains like cancer treatment and medical electronics, condition monitoring in wind-power, test and measurement and the product development organizations span Europe and the United States. TwinCAT has been used for applications like controlling radiation dosage, Focus control of Proton rays, PID and motion control for prosthetic feet testing, gear-box testing, condition monitoring based on vibration analysis, dynamic data acquisition for analysis. This paper highlights the application of TwinCAT technology in product development

Index Terms ADS, CMS, CNC, CPU, DSP, Embedded PC, EtherCAT, IEC-61131-3, IPC, IP, PID, PTP, NC, NI, TwinCAT PLC

  1. OVERVIEW OF BECKHOFF PRODUCTS AND TECHNOLOGY

    BECKHOFF Automation GmbHs core technology for PC-based Automation is called TwinCAT (The Windows Control and Automation Technology). The product envelope of BECKHOFF spans Industrial Grade PCs, Embedded PCs, I/O terminals, motor-control terminals, stepper motors, servo- drives, servo-motors, linear servo-motors. Special I/O modules are available for oscillation measurement, strain gauge, power measurement, communication, etc. TwinCAT provides for PLC, motion control, Interpolation, Transforms for Robotics, Soft CNC, measurement functions for condition monitoring, controller toolbox and so on. Other libraries for Matlab/Simulink interface, Automation Device Specification (ADS) for Matlab or NI LabVIEW are available in the TwinCAT platform. Supplemental libraries are available for Building Automation, Web server, RFID S5/S7 communication interface.

    TwinCAT provides a real-time soft control kernel which converts the PC running a Windows OS or the Embedded PC with Windows CE into a control platform on which the product companies Intellectual Property IP resides.

    Another key aspect of the technology is EtherCAT (Ethernet for Control Automation Technology). In EtherCAT devices, all protocol processing is performed in the interface hardware, rather than in software based protocol stacks running under an operating system. In serial communication also, the protocol processing is done in the interface hardware, but the layer 2 Ethernet MAC does not come into play. The approach to protocol processing in EtherCAT can give an I/O update time for 1000 I/Os of

    only 30 µ seconds including the I/O cycle time.

  2. SYNOPSIS OF APPLICATIONS

    Intra Op Medical in the United States (US) has developed a technology called Intra-Operative Electron Radiation Therapy (IOERT). This technology uses a TwinCAT PC- based controller for administering radiation dosage in cancer surgery. In another application for testing Prosthetic feet, the testing machine has to repeat standardized tests and angle profiles during the stance phase evenly two million times. In Gear-box testing, it is necessary to acquire data at a fast rate, in order to record, archive and display important parameters.

    A mechanism has been implemented in Condition Monitoring systems (CMS), so that interference signals can be ignored, by 8.2 Monitoring of Germany using TwinCAT and EtherCAT Inputs/Outputs (I/Os). It is possible to use a mechanism of interference analysis of accelerometer data from turbines in order to do Condition Monitoring (CM) of wind turbines. Proton radiation therapy is used in cancer treatment without affecting non-cancerous other organs. Adaptive control algorithms have been used for analysis of dynamic, hydraulic and thermal loads on components without using proprietary measuring cards and Digital Signal Processors (DSPs).

  3. DESCRIPTION OF THE APPLICATIONS

    It is possible to align an electron beam for administering radiation dosage using a TwinCAT PC-based controller and a pair of stepper motor terminals and stepper motors. This technology is being used to radiate the zone from which a cancer tumour has been surgically removed, during the surgery itself. This has been developed by IntraOp Medical [1] and the technology developed is called IOERT. The machine developed is illustrated in Fig. 1 in the following page. The product is called Mobetron® and the TwinCAT technology is used to automate a small mobile linear accelerator. The TwinCAT PLC and Numerical Control (NC) Point-to-Point (PTP) functionality is used on a CX5020 (an embedded PC type based on 1.6 GHz Atom Processor). IntraOp Medical uses Beckhoffs EL7031 and EL7041 motor control terminals paired with AS1060 series stepper motors.

    Fig. 1. IOERT Machine

    BECKHOFF Technology has been used for developing testing machines for prosthetic feet by Otto Bock Healthcare in Germany [2]. Prosthetic feet are used by people who have lost the limb. The testing machines repeat the standardized stress and angle profiles during the stance phase evenly two million times. The tests are done on newly developed prosthetic feet according to ISO standards and that need to be contemporary, highly functional and reliable over a long time.

    This kind of testing machine is equipped with a standard pneumatic cylinder with two proportional valves, a BECKHOFF servo drive with EtherCAT interface, a BECKHOFF servomotor and planetary gear unit with a power of 4.5 KW, various power and position sensors as well as TwinCAT PLC software running on a BECKHOFF Industrial PC (IPC). The IPC controls up to four test modules simultaneously via EtherCAT. The problem, in this scenario a combination of a prosthetic foot and pneumatic cylinder provides a complex interaction which constantly changes throughout the simulated stance phase and is also influenced both by the type of foot construction as well as its size and wear in the testing machine. The prosthetic foot reacts differently with every rolling motion.

    The servo drive chosen for the foot plate controls the foot position with the necessary precision even under considerable stress. The pneumatic cylinder is controlled via two proportional valves according to the direction in which the piston moves. In this way, the force can be controlled in both the directions (up/down) and controlled via the air introduced. The system is controlled via the PLC with a cycle time of 5 ms (200 Hz). A walking cycle lasts 1 s (1 Hz). The foot position is crucial for the measurement. For this reason, a PID position controller is used at the end of the stance phase when the force controller is no longer activated as shown in the system design diagram in Fig.2.

    In order to examine the system responses, the force progression was regulated by the valve controllers. In the process, the position controller and the force controller were used, the former in closed control loop and the latter in open control loop. At every angle of the foot, the amplitude deviates from the set value by a different amount according to the system characteristics of the prosthetic foot. Using a PID controller with different parameterization for each point of the Curve did not produce a stable signal. A separate PID controller was used for each plate angle. Each PID controller works in its area of the total curve. Information from the last test series is used to correct the force errors in every point. Changing the parameters of each individual controller makes it posible to justify the controller output for each area of the curves separately.

    An Endurance test bench was developed as a project for testing the gearbox synchromesh mechanism of an Audi A4 2.0 TDI by EDAG-Prftechnik projects [3]. The objective of the test is as the gearbox is driven at a constant speed under no-load conditions, two gear changes are performed per minute and the important characteristics are to be recorded, archived and displayed. One of the main requirements is to keep changes of speed as low as possible during the individual gear changes. In the original test set up a large gyrating mass was used for this test method. The main objective for the development of a new test bench was to dispense with the gyrating mass while at the same time, achieving the same or better results. The new solution

    foresees the acceleration of the gear box on the output side in second gear up to the nominal speed and followed by energy free shifting to first gear. As a result of the existing mass inertia, there is a drop in speed that needs to be compensated by the electric drive. The drive must also supply the energy required to accelerate the clutch disc when shifting from second to first gear. The control requirements needed a fast, deterministic I/O system for the acquisition of the actual speed data and the transmission of the control set point values (max cycle time of 500 µs) as well as a correspondingly fast and deterministic control computer for calculation of the set points (max cycle time of 500 µs). The CX1020 Embedded PC with TwinCAT PLC forms the integrated platform for the real-time control and PLC tasks. The drive and the remaining I/Os are networked with the CX1020 via EtherCAT. Of crucial importance is the fast reaction to the gear change information, so that the drive can compensate the imminent drop in speed in real-time. This information is transmitted from the sensor to the controller via EtherCAT in less than 100 µs and enables an immediate reaction of the drive to the gear shift. In this application, TwinCAT also uses its ADS communication DLL to help integrate the data in LabView.

    Fig. 2 System Design Diagram for Prosthetic Foot Testing

    BECKHOFF Technology can be used in the dynamics domain [4] for acquiring data for analysis. TwinCAT controller and EtherCAT I/Os can be integrated with application-oriented analysis and data management software for condition monitoring of wind farms in order to provide more intelligent Condition Monitoring System (CMS).

    Standard CMSs still work in stand-alone mode, i.e., independent of the equipment or machine controller. In many cases, particularly in retrofitted systems for wind turbine applications, the conclusion as to whether an unusual state has occurred is based purely on the speed at which the turbine rotates. In some cases, the actual output is used as a supplementary parameter. Standard systems, which dont receive additional information from the controller regarding the external influences under which the machine is currently operating, are prone to issuing false warnings and false alarms. This has been used by the BECKHOFF customer 8.2 Monitoring, operating out of Hamburg. The schematic in Fig. 3, illustrates a model of a CMS integrated in a wind turbine controller

    A controller integrated CMS receives additional information from the controller regarding the external influences under which the machine is currently operating, so that the CMS can ignore interference signals noise related to yawing or pitching, activation of auxiliary or sub-normal oil temperatures. Suitable algorithms in the CPU of the controller which log the actual data can be used to access the quality of

    the stored raw data.

    The BECKHOFF customer Ortosense [5] of Denmark has developed technology for condition monitoring of wind turbines based on vibration analysis. The old technique has been based on Fast Fourier Transformations (FFT) used in order to detect changes or damage, for example in the gear unit of a wind turbine. FFT has the disadvantage that the result is strongly influenced by the speed, among other factors so that it is difficult to detect damped resonance frequencies in the spectrum. Ortosense has developed an oscillation and vibration analysis technique that is insensitive to changes in speed and is therefore able to determine resonance frequencies with much higher accuracy than other frequency analysis methods. The Ortosense technology, referred to as Auditory Perceptual Pulse Analysis (APPA) is based on interference analysis and has overcome the problems associated with FFT. It perfectly mimics the sound perception ability of the human ear and enables reliable monitoring of wind turbines. One of the products developed by the company based on the APPA technique is called Easy TurbineAnalyzer. The recorded data are processed and analysed with TwinCAT PLC software from BECKHOFF and subsequently compared with carefully selected reference data. As soon as the deviation from the reference data is detected, the TurbineAnalyzer automatically sends a warning signal to the operator via SMS. The collected data can be copied from the analyser to a standard USB flash drive on a regular basis. The BECKHOFF control platform used for this product consists of a DIN rail mountable CX9001 Embedded PC with two directly attached EL3632 EtherCAT condition monitoring terminals. The schematic shown in Fig. 4. gives an illustration of the Easy TurbineAnalyzer plug and play solution for condition monitoring in wind turbines. In practice, three accelerometers are attached to different measuring points with strong magnets, e.g. at the planetary gear, the rotor shaft and the generator shaft. In addition, the generated current can be measured by applying a terminal around the main cable.

    An innovative proton radiation technique has been made into a product by Accel Instruments GmbH [7] and supplied to the Munich-based Rinecker Proton Therapy Centre (RPTC). The Proton irradiation equipment is controlled using BX3100 Bus Terminal controllers and CX1000 Embedded

    PCs from BECKHOFF.

    Coming to the background, a common aspect of X- rays and Proton rays is that they can be focussed very accurately. The main difference is that the range of protons can also be controlled very accurately. This is due to the fundamentally different physical properties of electro- magnetic waves (X-rays) and accelerated nuclear particles (protons). Proton rays release the majority of their energy at a specified penetration depth in the affected tissue. The treatment does not affect the non-affected organs as much as in traditional cancer treatments. The other advantage is the energy density at the focus of the tumour is significantly higher than in conventional photon treatment and the prospects of curing the disease are better.

    Coming to the technique, in a particle accelerator (cyclotron), protons with strong electromagnetic fields are accelerated along a spiral to 60% of the speed of light 180,000 km per second. When the protons have reached the desired speed, they are deflected via an electric field and leave

    the cyclotron in a straight line. The schematic in Figure 5 illustrates the equipment.

    Coming to the implementation, in order to ensure that the proton ray reaches its target precisely, 182 deflection and guide units guide the ray directly into the cancerous tissue. The proton ray travels inside an approximately 160 m long evacuated stainless steel tube system. For monitoring the vacuum in the tube system, five independent measuring systems are controlled and analysed via a BX3100 Bus Terminal controller with PROFIBUS interface. BX3100 terminals with KL6001 serial RS232 interface are used for data acquisition purposes.

    Fig. 3. Condition monitoring system integrated in a controller

    Fig. 4. CM of wind-turbines with vibration analysis

    The deflection and guide units consist of special electromagnets that are controlled via high precision power supply units. 10 CX1000 mbedded PCs, each with RS422 interfaces, are used for continuous communication with the power supply units for the electromagnets. To this end, data packets are exchanged between the CX1000 and the coupled power supply units with a cycle time of 2 milli-seconds. This implementation required very fast calculations and a very high data throughput.

    Dr. Ecklebe GmbH [6] has used EtherCAT in a project to upgrade a test bench for hose clips for analysing dynamic, hydraulic and thermal loads on components. In this project EtherCAT replaced proprietary measuring cards and digital signal processors. With TwinCAT PLC software and EtherCAT as a fast field bus system all control tasks are created in the IEC-61131-3 programming language. The system features cycle times in the 50 µs range. Since the hydraulic pressure values have to be kept constant during the test procedure, fast readjustment is required. EtherCAT, in conjunction with TwinCAT provides a modular high

    performance control system, based on cost-effective, standard components.

    The adaptive control algorithms developed run within a dedicated task (500 µs) in the software PLC. All other tasks are handled via a second task (1 ms). The following tasks have to be dealt with:

    1. Calculation of the set value curve (sine, trapezium, rectangle, etc.),

    2. Position control of the pressure generator,

    3. Regulation and monitoring of the test pressure,

    4. Adaptation of the control parameters, and

    5. Logging and pre-processing of all measured values.

    TwinCAT integrates the regulation process into the control program. The TwinCAT ADS is used to write the process parameters to a visualization program. With this hardware

    PLCs and DSPs are not required. This not only leads to substantial cost savings for components, but also reduces the project design, switch gear engineering and programming effort.

    Fig. 5. Particle Accelerator

  4. APPROACH FOR USE OF BECKHOFF PRODUCTS IN PRODUCT DEVELOPMENT

    The requirements need to be analysed to decide on the appropriate configuration of the TwinCAT soft control platform spanning PLC, PTP, NC Interpolation, CM, etc. Apart from this in certain cases, the controller tool-box may have to be selected. After the selection of the TwinCAT platform, libraries and supplements, the appropriate implementation hardware platform like Industrial PC (IPC) or Embedded PC must be selected. The Central Processing Unit (CPU) can scale up from 400 Mega-Hertz (MHz) ARM to an i7 Quad Core CPU in the BECKHOFF range of PCs. The mechanical Mechanism or combinations of mechanisms must be analyzed to decide on the motors and the drives needed for the motors. The appropriate architecture of the EtherCAT network must be decided next. The software design must be taken up next. The implementation process will need control panel and mechanism controls implementation followed by the integration of control panel, mechanism and control software. The last step will encompass trials, fine tuning and refinement. Field trials will be the last step.

  5. REFERENCES

  1. BECKHOFF Automation and IntraOp Medical of U.S.A, Innovative radiation therapy uses flexible PC-based control platform Health care: Matrix controller for simple, accurate

    control of non-constant, cycle set profiles, PC Control Magazine, Issue 2, 2013

  2. BECKHOFF Automation and Otto Bock Healthcare GmbH, Gernany, Complex Control Technology, Simple Implementation Health care: Matrix controller for simple, accurate control of non-constant, cycle set profiles, PC Control

    Magazine, Issue 3, 2009

  3. BECKHOFF Automation and Edag Prftechnik, Germany, EtherCAT enables revolutionary new automotive test bench concept with no gyrating mass implementation Syncromesh

    mechanism for gearboxes on test benches, PC Control Magazine, Issue 3, 2010

  4. BECKHOFF Automation and 8.2 monitoring GmbH, Germany, CMS: Filtering out background noise, PC Control Magazine, Wind Special, 2012

  5. BECKHOFF Automation and Ortosense Denmark, Control monitoring of wind turbines based on vibration analysis, PC Control Magazine,

    Wind Special 2012

  6. BECKHOFF Automation and Dr. Ecklebe GmbH, Germany, ËtherCAT innovation for test bench EtherCAT replaces proprietary measuring cards and Digital Signal Processors, PC

    Control magazine, Issue 3, 2005

  7. BECKHOFF Automation and Accell Instruments GmbH, ÉtherCAT CX1000 supports advanced medical engineering Innovative high-tech Cancer treatment, PC Control Magazine, Issue 2, 2005

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