Motor Supplier uses VisSim to Improve Machine Design

Contributed by William M. Erickson, Staff Engineer, Indramat Division, The Rexroth Corporation

As a supplier of servo motors, drives and computer controls, we gain a substantial competitive advantage by being able to guarantee to our customers that the motors and drives we select will achieve the required performance criteria. Our customers are machine builders who use our servo products to perform motion control in a variety of applications, ranging from high-speed spindles to low-speed rotary tables.

Consider the customer who requires a very precise bandwidth (a measure of how well the real-world application follows the control command). We don’t want to supply a motor whose torque and velocity are so strong it will excite resonances in the machine. Given the mechanical load, the mass of the customer’s machine, and other factors, we determine the appropriate motor and drive, along with the exact set of control parameters.

We have to guarantee to the customer that these parameters will deliver the required performance bandwidth. Until recently, we provided that proof by testing the components in our lab. We would take the selected motor and drive from stock, connect them to a large steel wheel having the same mass as the customer’s machine and then run tests for half a day.

An alternative to this time-consuming process would be to run simulation software to test the components. Initially we were not encouraged by the simulation software we had tested… until we learned about VisSim, an interactive Windows-based modelling and simulation software program. We liked its ease of use, so I ran some simulations with VisSim and compared it with our lab results. VisSim’s predictions matched the lab results on enough tests to convince us of the accuracy and reliability of the software.

I began using VisSim on a regular basis to select the correct motor and drive systems for our customers. The simulations modelled the function of our motor and drive with the function of the customer machine, integrating the mechanical load and electrical properties of the components into a system. VisSim provided two critical components used in selecting a motor: motor velocity and motor torque. Equally important, I used VisSim to assure customers that the selected motor and drive would give them the performance they required.

One of our more critical applications was to assure a customer that our frameless motor technology would provide the solution for optimising the machine-motor fit of a new machine. Responding to market demand for smaller machine volume, the customer’s engineers wanted to downsize the motor volume. Frameless motors seemed the perfect answer. Without a pre-defined frame casing, shaft, bearing structure and cooling package, frameless motors can be as much as one-seventh the volume of conventional framed motors, while achieving the same power rating. They are installed as individual components (a rotor, stator and feedback assembly) and become integral parts of the machine.

The customer’s management would not provide final authorisation for the design until they were confident that it would perform as predicted by the engineers. To assure management of the motor’s performance capabilities, I simulated the machine with the frameless motor, drive and computer control using VisSim.

Because I was able to guarantee that the motor configuration would meet customer specifications, the customer’s management approved the design. The project probably wouldn’t have proceeded without VisSim, and I wouldn’t have had the time to extensively test the machine-motor configuration in the lab. But through simulation with VisSim, I completed the testing in a few hours.

By replacing the conventional motors with the frameless motor, the customer built a machine not only with smaller volume, but with several key advantages: the stiffer frameless motor yields improved product quality, and the options for configuring shafting and bearing structures offer more flexibility. In addition, the cooling system is more efficient and the performance is quieter.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

Honeywell Models GE Gas Turbine with VisSim

When Honeywell UK won a contract to retrofit an existing control system on a General Electric LM2500 gas turbine, they required a simulation package that had the power and flexibility to model the non-linearities of a turbine, as well as evaluate the relationship between the turbine and the controller. Based on previous experience, Mohan Thiagarajah, applications consultant at Honeywell, chose VisSim to handle all of their development and testing needs.

After only a few weeks, Thiagarajah created a basic model of the gas turbine, including the compressor, combustor, gas generator turbine, and power turbine. Several iterations later, the model grew to over 2,000 blocks and encompassed all the auxiliary units, including fans, pumps, values, and pipes. According to Thiagarajah, features like VisSim’s drag-and-drop block placement and compound blocks streamlined model construction and greatly improved the readability of the diagram.

One of Thiagarajah’s prime concerns was integrating existing GE information into the overall model. In particular, Thiagarajah wanted to model the starter motor, ignition system, ventilation fan, and lubrication oil pumps based on GE specifications. “The map block provided an easy and reliable way to incorporate this data directly into the simulation,” explained Thiagarajah. “I could perform 1-, 2-, or 3-D table look-ups, depending on how the data was organised.”

With a fully functioning model, Thiagarajah was able to create and validate complicated control algorithms for start-up sequencing and fuel controls, and simulate both the transient and steady-state behaviour of the system. He also had a safe environment in which to test emergency trips and alarms that would be too costly or dangerous to perform on the physical system.

In the end, both Honeywell and their customer were extremely satisfied with Thiagarajah’s work. Honeywell found that VisSim was the most effective and easiest PC-based solution for developing complex simulation models. Honeywell’s customer ended up with an operational system that met all their requirements.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

The Air Force Uses VisSim For 6DOF & Weapons System Design

Using VisSim, the Air Force Research Laboratory (AFRL) at Eglin Air Force Base, Florida has developed a high-fidelity 6-degree-of-freedom (6-DOF) modelling system that simulates the flight dynamics and performance of a state-of-the-art weapons system. The modelling system was built under the Munition Simulation Tools and Resources (MSTARS) project at AFRL by a joint government/contractor team led by Larry Lewis, Munition Flyout Team Leader.

Designed for the rapid prototyping of new guided bomb and missile concepts, as well as the evaluation of new technology performance, MSTARS includes a library of VisSim-based munitions subsystems representing the accelerometer, rate gyro, autopilot, seeker, inertial navigation system, control surfaces, and air vehicle, with complete 6-DOF flight dynamics. Simplified models of a launch aircraft and threat target are also incorporated into the component library. Nearly 70 VisSim models and DLLs are currently in the library, and many more are being added monthly. Several guided bomb and missile 6-DOF simulations have been built using these components.

The current MSTARS system is the culmination of work which began when Lewis first created a prototype 6-DOF simulation using VisSim. “We had been using another modelling system which simply was not meeting our objectives. After doing a detailed comparison of several outstanding products, my team decided to go with VisSim for MSTARS. It was a scary prospect to re-do our previous work, but we accomplished more in one year than we had in the previous three years.”

According to Lewis, numerous VisSim features were essential in building the 6-DOF system. “Embed blocks allowed us to build a truly reusable library of components,” said Lewis. “And path aliases tied to the embed blocks let us specify a complete simulation configuration, eliminating the use of lengthy file specifications.”

Lewis emphasised that this modular approach to system design not only saved valuable time during the design and debugging phases, but also allowed engineers to quickly test the effectiveness of new subsystem component designs. “Whenever we came up with a new design, we just changed a single name to swap the new component into the simulation.”

Reuse of legacy code written in Fortran and Ada was facilitated by VisSim‘s DLL capability, as was the creation of new models and special utilities. “This ability to reuse existing code and create special-purpose code via DLLs shaved months off our development schedule,” said Lewis. New DLLs are constantly being added, written in C++, FORTRAN, and Ada 95.

In large model design, the dynamics of the system generally demand multirate simulation. In the 6-DOF system, discrete transfer functions, unit delays, and automatic DLLs were used to achieve different update rates. “This allowed us to dramatically reduce computation time and speed up the simulation,” explained Lewis.

Within the Eglin AFB community, VisSim and the MSTARS modelling system have received favorable reviews.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

DuPont & EnTech Use VisSim/Real Time for Dynamic Process Control Simulation

Written by Hank Graeser (DuPont) and Andy Waite (EnTech)

In a joint effort, engineers from E. I. DuPont de Nemours and EnTech Control Engineering used Visual Solutions’ VisSim software, and its real-time add-on package VisSim/Real-Time, to develop a high-fidelity dynamic simulation model of DuPont’s non-woven sheet manufacturing facility in Richmond, Virginia.

The model consists of approximately 31,500 blocks and 250 differential equations and simulates roughly a half dozen interrelated processes. It is used by DuPont’s control and design engineers to verify process dynamics during product transitions; develop and tune control strategies; and explore possible design changes to enhance control performance. In addition, system operators train on the model to maintain proficiency and learn new procedures without impacting plant operations.

According to Hank Graeser, senior engineer at DuPont,”VisSim is a highly intuitive environment for developing large scale high-fidelity process models. The DuPont Spruance model, developed in VisSim, has saved the company an estimated one million dollars to date. We developed the model in a third of the time it would normally take using conventional methods. VisSim’s block diagram interface made it easy to document and maintain the model. Every time we use the model for control design and off-line tuning, DuPont saves significant dollars as plant down time is reduced. We also train our operators using the VisSim model.”

The Ideal Simulation Software

As DuPont engineers drew up the specifications for the model, EnTech engineers were tasked with finding the best simulation software with which to build it.

The sheer scope of the model, which included the entire DuPont facility 15 tanks; 20 sets of pumps, lines, and valves; refiners; headbox and drainage table; vacuum devices, dryer cylinders, and scanning sensors warranted a simulation software package capable of modelling and simulating large, multivariable dynamic processes with a high degree of fidelity.

The software had to be interactive and graphically oriented so that dynamic information could be presented in an intuitive manner. In addition, the block set had to include a complete selection of continuous, discrete, transfer function, Boolean, arithmetic, and I/O blocks.

Other key requirements included the capability to run in simulated time, real time, and continuous time; drive real-time analogue and digital I/O; stop and continue simulations; initialise all state variables; and extend the block set with custom blocks written in C, for enhanced speed and additional functionality.

Because system operators would also use the simulation model for training purposes, the ability to create realistic control panels with controller faceplates, dynamic tank levels, and built-in alarms was also important.

Based on these requirements, the simulation software that best met EnTech’s needs was VisSim and the VisSim/Real-Time companion software.

Model Design

According to DuPont and EnTech engineers, the DuPont model simulates the outputs of 80 sensors and transmitters and accepts input from 50 controller outputs. In addition, the model provides high integrity dynamics as “seen” through the eyes of the actual sensors and transmitters, with a time constant in the range of about 3 seconds. This means that the truly fast dynamics, such as that of incompressible fluid flow, which typically have time constants of 20 milliseconds, do not have to be solved rigorously. Instead, the equations associated with the pump curves, fluid flow, and control valve characteristic curves can be approximated by solving only the nonlinear algebraic equations.

These “algebraic loops” involve the on-line iteration from the last known flow and are solved using algebraic loop time constants of typically 1 second, which provides an adequate safety margin compared to the high-fidelity specification of 3 seconds.

In the resulting simulation, the time constant spread ranges from a fast value of 1 second to that of the mixing time constant for some tanks of 20 minutes. This time constant spread, even though quite large, means that the simulation avoids some of the pitfalls of “stiff systems of differential equations” which are very difficult to solve numerically.

The final simulation model is organised in a multi-layer format in which detailed simulation sub-elements collapse into “compound blocks.” There are 900 compound blocks, in about six layers, organised in an easy-to-follow, process-oriented layout.

Model Verification

In the testing phase, close to 200 real-time I/O channels were used to validate the model and control hardware. The simulated process runs ten times faster than the real process on a Pentium 100 MHz personal computer, at a simulation step size of 0.5 seconds.

Predicting The Future

The DuPont model is an excellent example of how a dynamic multi-variable process control model can be developed and utilised using VisSim and VisSim/Real-Time. Graeser and other DuPont engineers have observed a “close match” between model and actual plant data. Based on these results, they are confident that the DuPont model can be used as a “life-cycle” tool to faithfully predict the effects of future design decisions before modifications are actually made to the plant.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

VisSim modelling for the future

Simulation provides insight and saves training time at Surry Power Station.

A state-of-the-art, hands-on training program was developed at Surry Power Station to improve the skills of operators in the use of controller modules that operate steam generator power-operated relief valves. The steam generator controller modules operate automatically or manually to open or close relief valves that allow for safe venting of pressures that build up in the reactor’s three steam generators during shutdown.

“I developed computer-based simulations that allow operators to change controller settings, analyse the effects of the changes, then explore them mathematically,” said Hal Warren, senior instructor-Nuclear Training, Surry Power Station. “This helps them develop a better understanding of the effects generated by each change.”

Warren developed a second simulation that depicts how station equipment responds to certain types of emergency events. “It also explores operation of the atmospheric dump valves in automatic and manual modes, as well as common system failures that can occur and the actions that need to be taken by operators,” he said.

“The simulations can be used at an employee’s workstation or can be projected in a classroom environment to provide a rapid method for understanding complex process controller concepts.” Warren’s simulations were designed on a Pentium PC using VisSim modelling and simulation software. He said the feedback received from trainees indicated an improvement in the assimilation and retention of the training material, and instruction time was reduced from 10 hours to two hours.

“The simulations also provided us with a new method of troubleshooting systems and equipment without impacting station operations,” he added.

For his efforts, Warren was awarded a Training Excellence Award from the American Nuclear Society for achievement, excellence and innovation in nuclear training. The simulations were also recognised by the Institute of Nuclear Power Operations (INPO) during a 1995 plant evaluation.

The Training Center at the Surry VA power station is tasked with providing continuing education for its operating personnel in a formal classroom environment.

VisSim is a visual block-diagram based modelling and simulation applications environment that runs on Windows and UNIX/X platforms. Along with VisSim/Real-Time add-on software, it is an ideal tool for modelling controls and plant functions for the purpose of commissioning new processes and for training operators.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

Carrier Uses VisSim for HVAC Design

Carrier Corporation, a division of United Technologies Corporation, is one of the largest manufacturers and distributors of Heating, Ventilating, and Air Conditioning (HVAC) equipment worldwide. For more than five years, Carrier has been committed to using VisSim to model, simulate, and validate product designs ranging in scope from single zone air conditioners to hundred-ton chillers used in hospitals, university campuses, and office complexes.

Richard Kolk, senior staff engineer in controls and simulation, explains why and how Carrier uses VisSim:

“Due to its power, flexibility, ease of use, and low cost, VisSim has been Carrier’s choice for system modeling, simulation, data acquisition, and rapid prototyping for each of the past five years. VisSim’s power covers both scalar and vector block diagrams including such features as matrix operations, matrix output displays, expression blocks, and a model tree.

These features enable complex real world systems to be rapidly modelled, simulated, and debugged. Modelling of essential matrix-based control elements, such as state space controllers, observers, and Kalman filters becomes particularly easy with the new matrix operations.

Carrier uses VisSim to develop and test all of its electronic controls and depends on the resulting shortened development times to continually merge new technology into its products. Products which would have taken two to three years to develop in the past are now routinely completed using VisSim in less than one year.

A recent VisSim modelling effort conducted by Dr. Fred Cogswell, senior scientist at United Technologies Research Center, focused on the development of a reciprocating chiller model for simulating faults. The reciprocating chiller consisted of two refrigerant circuits, each with the following components:

  • One to four reciprocating compressors in parallel to compress the refrigerant vapour
  • A water-cooled or air-cooled condenser to remove heat from the high pressure refrigerant and condense it to liquid
  • A stepper motor controlled expansion valve to meter the refrigerant flow as it goes from high to low pressure
  • An evaporator to transfer heat from the chilled water to the refrigerant, thus boiling the refrigerant to vapor while providing cooling.

The model, which consisted of approximately 6,000 blocks, performed a dynamic simulation of the chiller system tracking the migration of refrigerant between components as well as the control interactions. It ran at an update time of 1 second in order to maintain stability between the components; however, on a Pentium computer it was capable of running many times faster than real time.

This reciprocating chiller model represents one of the many ways Carrier Corporation uses VisSim to significantly decrease its design cycle time.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

GM Delphi uses VisSim to Reduce Brake Control System Prototyping Time from two Months to two Days

In the past, it took up to two months of special machine shop work, circuit design, hand coded software development and in-car testing to determine whether a design was feasible for production. Now, with the combination of fast and powerful block diagram-based modeling and simulation software from Visual Solutions and highly reliable, noise-immune data acquisition cards from National Instruments, such testing can be done in two days or less.

GM Delphi configured a system of VisSim running on a lap top with two PCMCIA DAC Card 1200s, 16 analogue inputs, 4 analogue outputs and 16 digital I/Os. With their complex control system, they achieved closed loop sampling rates of over 200 Hertz running a 100 MHz Pentium laptop. VisSim/Real-Time is capable of closed loop sampling rates of up to 5000 Hertz depending upon the complexity of the closed loop system and the CPU speed.

A typical use of this setup is to test out electronic braking assist equipment. Both the closed loop control as well as data logging can easily be developed and configured with VisSim. Once the sensors and equipment under test are installed in the vehicle, it is a simple matter to mount the laptop in the passengers seat, secured with a standard 2″ nylon web tie-down, then plug in the ribbon cables to the DAQ Card 1200s, and turn on the laptop. Because it is difficult to view the laptop display during daylight driving, an LED display panel, driven by the digital I/O of the DAQ Card, is used for critical function monitoring. Five-minute runs with strip charts tracking user inputs, pedal pressures, accelerations, controller outputs are typical.

In over a year of use, VisSim has never failed during a real-time run. The system has proven robust under the harsh demands of vigorous brake testing, lack of good electrical ground, wide temperature and humidity variations common to Ohio, and general garage lab treatment.

We also use VisSim in lab bench situations such as automated performance testing of hydraulic valves. Using map blocks, it is easy to create time-based test sequences and correlate sensor outputs with command inputs. The wide array of plotting capability and data export makes it easy for data analysis. We feel that VisSim has been an important addition to the set of tools we use in automotive design and test.

Author: Gary Fulks, Senior Design Engineer at GM Delphi describes his use of VisSim & VisSim/RealTime

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone +44 (0) 203 695 7810, fax +44 (0) 203 695 7819, email info@alfasoft.com; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

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