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By Dan Hebert, PE, Senior Technical Editor
There are many different ways to test and verify that your machine and its automation system will perform as intended prior to final fabrication, installation and commissioning. Each test method has advantages and disadvantages, and different machine builders employ disparate testing methodologies depending on particular circumstances.
The main testing methods are software emulation, hardware simulation, prototyping and beta testing at a customer site. Many machine builders mix and match these test methods and also employ different testing protocols for different machines.
Software emulation just tests out the controller and HMI software programs. This entails writing a program to test the basic on/off and dynamic operation of the machine. Dynamic operations such as control of movements either are not simulated or are simulated in a simple form without detailed analysis.
Hardware simulation starts with a detailed and accurate software-based model of a machine’s hardware including dynamic operations, clearances and interactions among moving parts. A good hardware simulation takes lots of time and effort to develop but in the best case can simulate virtually the entire operation of the machine and even parts of the customer’s factory.
Test Methods from
1. Software emulation
Prototyping involves building all or part of a machine and its automation system. Prototype machines are tested in the shop to ensure correct operation. This is a step up in time and expense from hardware simulation. But many feel prototyping achieves better results than simulation.
A customer-site beta test requires installing a completed machine at a customer site and then testing the machine in actual production with all or part of a customer’s manufacturing line. This is the most expensive type of testing and requires a compliant customer, but there is no better way to verify machine operation.
We’ll examine some of the pros and cons of each test method, starting with the simplest and progressing to the most complex.
Software emulation is the most basic form of testing and is often sufficient for standard machines that have been in production for some length of time. “We use a combination of prototype parts and software emulation for machine testing,” says Paul Brancaleone, principal controls engineer at plastics processing equipment builder Gloucester Engineering in Gloucester, Mass. “Before software actually makes it to a machine, we simulate and test the response and sequences. We build debugging code into our programs using our source assembly language,” adds Brancaleone.
Software emulation is most useful for standard machines, but many machine builders find that these machines work well enough to skip the step and go straight to shop test. “We carry out a factory acceptance test on each machine with the customer before it leaves our manufacturing facility,” explains Ken Carter, general manager and president of EDL Packaging Engineers in Green Bay, Wis. EDL makes end-of-line packaging machinery.
“Emulation software for the PLC program might be useful, but I am not sure how much time it would save. It is fairly easy to modify the PLC program during the shop test if there are errors and if modifications are required,” adds Carter.
Another machine builder seconds Carter’s point. “We only spend 80 hours or less to program a machine prior to shop setup, so software emulation isn't necessary for us,” claims Wayne Kornelsen, supervisor of controls engineering at Priority One Packing in Waterloo, Ontario, Canada, a maker of palletizing equipment.
“If we needed to develop a new machine from scratch, we would need something that could simulate cycle times and both pneumatic- and drive-driven motion. One thing our company could use is a low cost simulation package for cycle time and throughput estimating. We have looked at Arena from Rockwell Automation and Simul8 from Simulat8 for this, but they are fairly expensive.”An example of this was an expander turbine start-up Maverick did a few years back. “When we got to the site the PLC’s ControlLogix program was incomplete and obviously untested,” says Gellner. “ We were not responsible for the PLC programming, but because of the propensity of the expander to upset the process, which could result in explosions, we set up a SoftLogix controller, loaded the PLC program, added some very extensive loop-back code, connected it to the HMI and shook out the wrinkles before we put it online.” Explosion avoided.
System integrator Maverick Technologies in St. Louis uses software emulation to shake the programming wrinkles before they go live. Read about Maverick's experiences in Integrator Uses Simulation to Close Design Loop.
For new and very complex machines, it is often necessary to move up from software emulation to a more demanding test protocol and hardware simulation requires lots of up-front time and effort because it’s necessary to build an accurate software model of the machine.
Simulating harsh operating conditions in the shop often requires a combination of hardware and software tools. “Simulation allows us to dynamically test our control panels for such things as fatigue, heat dissipation and vibration and shock,” relates Lee Hilpert, vice president of manufacturing and engineering at Kem-Tron Technologies in Stafford, Texas.
Kem-Tron makes shakers, centrifuges, de-watering units, de-silters, de-sanders and associated automated controls. These machines are deployed under tough operating conditions in oil drilling applications.
“We use SolidWorks and CosmosWorks for design and finite analysis respectively. We first use SolidWorks to model the control panel. Once this is complete we apply variable test parameters such as heat load, operation cycles and vibration using CosmosWorks,” explains Hilpert. He points to a new hazardous area centrifuge control panel as a good example of this. “We first modeled the enclosure and its heat-generating devices using heat coefficients, heat loads from the devices and expected ambient conditions,” he says. “We then ran a steady-state analysis to verify that we could dissipate heat without exceeding the specified temperature delta. Our equipment often experiences vibration during operation, so we have to ensure that control panel mountings and vibration isolators are designed correctly. We check that vibration will not cause a fatigue failure, and we also verify that we can withstand a single cycle shock load by dropping the unit from a specified level. Lastly, we use motion simulation to verify that we can fully open doors for maintenance access,” concludes Hilpert.
For the motion simulation Hilpert uses CosmosWorks. “Once the device to be tested is fully modeled, we apply motion constraints that define how the part to be analyzed can move in space,” he continues. “For instance, if it is a door, then we would apply a series of constraints that would allow it to rotate around an axis defined by the axis of the door hinge pin. We can then open and close the door by just selecting it and using the mouse to move it or by defining the amount of free rotation in degrees. With this we can see if the door will open fully without hitting such things as handrails or other obstructions that could interfere. If the door, due to limitations of design, does come in contact with an obstruction such as a handrail, we can make sure that it does not hit a light or button on the front of the control panel.”
Hilpert thinks SolidWorks is very easy to use compared to other Solid Model/FAE software. “If you check some of the user groups, you’ll see that most engineers will concur with that opinion,” he says.
Hardware simulation often is required when the final intended machine operations can’t be easily duplicated during shop test. Hydraulic machines that must generate tons of force to handle very heavy loads are a good example.
Hawkeye Pipe in Mediapolis, Iowa, manufactures machines that pour segments of concrete pipe (Figure 1). They use a Delta Computer Systems’ simulator to generate sample points for moves, and they watch the simulator graph out the target and actual positions of the motion arm.
“The huge advantage of using the Delta motion controller is its simulation and graphing capability,” states Hawkeye engineer Ben Schmidgall. “Using our old system, I had no way of monitoring the motion, so there was no way to tell if the system was tuned precisely. Now, I know when the system is well tuned without having to perform often dangerous or expensive tests on real equipment.”
Complex Machines Benefit From Hardware Simulation
When a machine builder is putting together a complex machine with interactions among multiple moving parts, hardware simulation can be invaluable.
“We always make software simulations of our hardware,” says Dick Sidell, vice president and CTO for Micro Component Technology in Northboro, Mass., a manufacturer of strip test handlers and laser marking handlers for semiconductor applications (Figure 2).“Our simulators expose our control system to the same sensors, controls and motors as expected in the final product. We then develop, debug, and test the control software and user interfaces by connecting them to the simulated hardware.” MCT codes the software simulation of the hardware, the controller program and the HMI program using Microsoft Visual Studio .NET 2005 with a combination of C++ and C3 with both managed and unmanaged code.
Interestingly, MCT writes the controller and the simulator code in a double-blind experiment fashion. “The hardware simulator and the controller software are different programs, often coded by different people,” reveals Sidell. “Double blind coding ensures that the simulator is designed around the hardware and not per the controller program.”
During test, says Sidell, MCT normally has two windows open on one development computer. One window represents the view of the hardware. It also displays the current states of digital inputs to the hardware—digital outputs from the controller; digital outputs from the hardware —digital inputs to the controller; and the current positions of all axes of motion—typically about 13 servo axes. The other window is the HMI for the controller.
“Our methodology takes a lot of work but pays great dividends,” says Sidell. “We can develop the controller while the hardware is still being designed and built. When we make mistakes in the controller, nothing gets broken. Multiple developers can work simultaneously without requiring duplication of hardware.”
MCT also uses its simulations for offline training after the hardware has been deployed. When trouble reports or feature requests come back from the field, they use the simulation instead of the actual hardware to correct the problems or add the features.
MCT does software development in various sites in the U.S. and abroad, and they manufacture in Southeast Asia. “Our software developers rarely see the hardware, and with our resource limitations we can’t afford to keep hardware available to engineers for development, so we use simulators,” continues Sidell.
“It is often quite tedious and maybe risky to get the hardware to the state in which a problem can be studied. With simulation, we can often get to the same state quite rapidly and we can repeat the situation many times without consuming materials,” concludes Sidell.
For a new and complex machine with demanding requirements, prototyping can be the best solution. “We generally don’t use virtual design in our development cycles, but rather use levels of prototyping,” relates John Klauser, principal electrical engineer at Speedline Technologies in Franklin, Mass. Speedline makes stencil printers, dispensers and ovens for printed circuit board assembly. The complexity in these machines is found in the four to 18 axes of motion that use extensive machine vision to align boards and perform process inspection. The control system is centered on an XP PC using custom software and has distributed controls at each modular subassembly.
“We build one or two prototypes, maybe three alpha machines and then a number of beta machines,” says Klauser. “The beta machines are installed at customer sites for detailed evaluation. While prototypes may use some mock-up assemblies, alpha and beta machines will be configured to the notion that we have for the final machine at that time.”
A third machine builder also uses prototyping, but in this case modules are built and tested first as opposed to entire machines. The GL&V Paper Group in Lenox, Mass., manufactures winders used for winding and cutting all sorts of paper.
GL&V subdivides its winders into modules including three drive systems for large motors up to 1,000 hp and five drive systems for smaller motors up to 100 hp. Other modules include a cutting system with up to 48 automatically positioned slitters, a spreading system, a core feeding system, a core cutting system and a roll handling system.
“Our key for designing, engineering and testing efficient control systems is modularization,” explains Volker Klocke, Ing, senior controls project engineer with GL&V. “We specify the functionality of each module and define the interface among the modules. This approach allows testing of individual modules and of the communications prior to machine assembly. If all the modules and communications are correct, the machine in its entirety will work as designed,” concludes Klocke.
Customer-Site Beta Testing
The ultimate test is to install and operate a machine at a customer beta site. This is the most expensive and time-consuming test method, so it is used only for new and complex machines.
“We use hardware simulation, prototyping and beta site testing to verify machine operation,” says Reggie Doddy, software engineer at Cincinnati Milacron in Cincinnati. Cincinnati Milacron makes plastics machinery including injection molding machines, extruders and blow molders.
Machine builders who use a customer beta site want to test their machines as thoroughly as possible before shipment. For a new computer-based control system that Cincinnati Milacron introduced in a plastics machinery application, they built a machine simulator to test the control system hardware and software. “The simulators had the same computer controls we used to run the machines,” says Doddy. “We added additional wiring to simulate the running conditions on the machine. The controls are from B&R Automation and we used their Automation Studio software to write the software for the simulators. Automation Studio works well and is easy to use. It allows you to use C, ladder logic or structured text to run the machine application. We're using C in our application. For the HMI software, we're using Automation Studio's Visual Components software. It's similar to Visual Basic. You can drag and drop objects to create screens. You can modify the objects by changing the properties of the objects.”
They then tested the control system on two test machines in their lab. Finally, they shipped one of the machines to a customer site less than an hour’s drive from their plant so they could respond quickly to any issues.
According to Doddy, their comprehensive approach to testing allowed them to correct most machine automation issues in the shop and expedited resolution of remaining problems found in the field. “Certain problems cannot be identified until the machine is running at a customer site. However, you have a better chance of identifying and resolving these issues quickly if you are not buried in other problems,” relates Doddy.
Doddy has several reasons why he thinks shop and customer site tests are needed even when simulation is employed. “Any simulation is only as good as the assumptions made,” he says. “If the simulation assumptions are faulty they won’t point out your problems, and you can spend a lot of time with minimal benefit.”
Prototyping and testing can be done in any number of manners or in any combination, but what works for you? Which tools are you using for simulation? Do you test in the shop or at the customer site? Sound off at ControlDesign.com/virtual.
Simulation Simplifies Material Movement
HK Systems in New Berlin, Wis., is an automated material handling and supply chain software solutions provider. HK Systems manufactures automated storage and retrieval systems, automated guided vehicles, conveyors and sortation equipment (Figure 3). It relies on a variety of machine and system test methods.
“We use software emulation, prototyping at our manufacturing facilities and beta testing at customer facilities,” says Curtis Doane, HK Systems technology manager for controls. “For individual machines, testing takes place in the factory. We’ll run storage and retrieval machines and automated guided vehicles on the test track before shipping to the site.
In some instances, the customer requests that the entire system be set up and run at our factory prior to installation. Although it’s costly, many customers see this as a way to reduce production downtime.”
HK Systems uses the AutoMod simulation software package, which is specialized for the material handling industry. “Compared to other discrete event simulation software, AutoMod requires a higher level user,” says Doane. “Its complexity is due in part to the source code interface required for modeling complex material handling systems. In addition, its load-based structure is not common among other simulation packages. Although it would not be considered easy to use, it is an industry standard for simulating complex material handling systems.”
During the proposal phases, simulation models are used prior to the engineering design to determine the function of the system and any issues with throughput. The software and controls logic most often is run against an emulation model that simulates the real world I/O to and from the PLC and allows complete checkout of the logic.
In some instances, especially for modernization projects, simulation or testing of the machine is not possible because upgrades are being performed on production equipment. In those cases, we rely on our expertise to ensure solid solutions.”
3D CAD Saves Weeks of Design
NC Electronics in Port Orford, Ore., designs, builds, and manufactures the Omniturn CNC family of turning machines. Richlin Machinery markets Omniturn machines east of the Mississippi and adds automation to these machines on a custom basis.
“We determine if the machine/automation combination will work using hardware simulation first, then in-house prototyping and, on rare occasions, beta testing in a customer facility,” says George Welch, president of NC Electronics.
“Most applications have similarities, and we use previously developed hardware and techniques as much as possible. The run-off for a particular application is done as thoroughly as possible in-house. Trying to correct a problem in a customer facility can be a nightmare because there is no on-site machining capability in case a component needs to be modified.”
NC Electronics makes extensive use of AutoCad Inventor, SolidWorks and TurboCad to check form, fit and function.
Richlin Machinery uses Inventor to develop and digitally construct automated loading systems for their turning machines. “With 2D CAD, it used to take us a at least a few days, sometimes a few weeks, to generate a rough layout of a machine,” relates Jeff Richlin, president of Richlin Machinery in Farmingdale, N.Y. “With a rough 2D layout and an experienced designer, we generated a rough quotation, always padded to anticipate issues during construction and run-off. With 3D representations of components we can digitally build a working model of our machine and automation process within days or even hours, and these models truly embody real world results (Figure 4).”
With 3D CAD, adds Richlin, an experienced machine designer can use the digital model of the machine to generate an automated bill of material, so a preliminary quotation is created almost automatically. “The conceptual model is sent to our potential customer,” he says. “If need be, we also use Inventor Studio to automate the model and generate visual confirmation.”
|Virtual design and prototyping are a controls engineer's best friend. Find out how the Control Intelligence Agency is leveraging that expertise. Watch the "CIA Virtual Brigade Briefing Trailer".|