By Don Talend
Simulation of machine performance impacts various facets of industrial automation, from mechanical and electrical to controls engineering. To the controls engineer, simulation could be described as virtual prototyping that reduces a products time to market and bridges the gap between production throughput and product quality.
From the viewpoint of an interdisciplinary product design and production team, simulation often can penetrate the information silos that typically have existed between functional areas of mechanical, electrical and controls engineering. Simulation tools have a collaborative capability since anyone on the team can determine the impact of design or control changes on the manufacturing process.
Simulation tools give controls engineers opportunities to get involved in the product design process from its origin and to test machinery virtually so it becomes operational faster.
One mission-critical application uses simulation to test the interconnection of wind energy systems to municipal power grids. Energy To Quality, a wind energy electrical services company in Madrid, Spain, tests wind farms with a mobile voltage-dip generator controlled by National Instruments LabView and a PXI/SCXI system. PXI is PCI extensions for instrumentation, a PC-based platform for measurement and automation systems that operates on the PCI bus standard. The PXI/SCXI system uses high-voltage input modules to measure secondary voltages at 110 Vac while controlling relays connected to tripping coils. The program creates electrical shorts to simulate faults prior to grid interconnection. and communicates results to a remote computer. The testing procedure allows operators to know immediately if the wind turbine complies with the requirements, enabling new wind farms to come online quickly without causing outages.
Trompeter Enterprises, Sterling Heights, Mich., an automation controls engineering firm specializing in automaking, uses Delmia Robotics, a manufacturing process simulation tool from Dassualt Systemes, to determine the positioning of welding and assembly tooling in its robotic simulations (Figure 1). A lot of times youre developing the tooling and you find out you cant get a weld done in a tight space, notes Matt Trompeter, president. Without developing it in simulation first, youre not going to find out until you get out on the floor. Trompeter says positioning problems in a process often result in the carmaker requesting a tooling change by the machine builder.
Figure 1: This digital prototyping tool allows automobile subassembly manufacturers to identify difficult-to-access areas for a robot or human before production begins on the shop floor.
Trompeter also uses the Delmia Quest advanced simulation tool to simulate various manufacturing scenarios with varying inputs such as facility layout, resource allocation and alternate scheduling scenarios in order to determine production throughput. It ties together robotic simulation for the robot and the simulations you get with the cycle times, combined with operator schedules and machine downtimes and gives you real throughput, he says.
Integrating Mechanical, Electrical and Controls
To Brian MacCleery, senior product manager, industrial and embedded design for design, deployment and embedded application developer National Instruments, Austin, Texas, simulation represents the biggest advancement yet in the concept of mechatronicsthe convergence of mechanical, electrical and controls engineering for more productive systems and higher-quality products. The catalyst for real progress in mechatronics, he says, is actually the replacement of mechanical controls with electronic controls.
For example, you have domains such as motion control that was almost completely controlled by the mechanical engineering team when it was gears and cams, he says. Now, the performance depends on how the PID controller is tuned, you have high-frequency drive circuits that pulse current through the motor at 20 kHz, and motion trajectories that have a huge impact on the mechanical system and the stresses, strains and torques it experiences.
Craig Therrien, product manager for 3-D CAD developer SolidWorks, explains that simulation via virtual prototyping represents an evolutionary step forward from traditional physical prototyping. By the time a physical prototype is available so the controls engineer can finalize the machine to manufacture the product under the traditional design approach, youre making panic-type fixes, adding weight to dampen vibration, slowing the throughput of your machine down so youre not having too much deflection, says Therrien. Youre doing things you really dont want to do. Youre doing a lot of extra work at the end that should have been taken care of at the front of the design.
The cause of this last-minute chaos, argues Therrien, is those information silos. Typically, you see a divide between controls people and mechanical systems designers, he notes. Usually theyll meet once at the start of the project and then they kind of go their own way. A lot of times near the end, the machine designers throw their designs at the controls guys and say, Make it work.
In recent years, NI has worked with SolidWorks to use and co-develop several simulation tools to eliminate machine and product design problems early in the development process. MacCleery recently wrote a white paper detailing the use of these tools, which will be used in a machine design guide NI is publishing. These simulation tools are designed to facilitate a system-level approach to development known as graphical system design.