JASON PALMER, DELTA COMPUTER SYSTEMS INC. 2017-01-25 17:48:57
MOTION CONTROLLER AND A PC Combined to cut costs in tensile test system retrofit. Sunnen Products Company of St. Louis, Missouri is a manufacturer of honing machines used by a wide array of OEMs including those in the aerospace, automotive, oil and gas and refrigeration industries to smooth and finish the insides of cylinders and pipes. To ensure that their machines will function reliably, Sunnen R&D personnel continually test the metals they use for both strength and durability. “We use tensile strength testing equipment to help us understand the physical properties of the materials that we use in our machines,” said Peter Kwentus, Sunnen engineer. PROBLEMS WITH OLD PLATFORM The company’s original tensile test platform was installed in the 1970s. It contained a PC based control system with paper plotter and a DV drive connected to a DC DV servo motor. The servo motor was connected to ball screws which caused a platen to move vertically to apply a stretching force to the specimen under test (see Figure 1). The test system used the load cell reading coupled with an encoder on the ball screw to plot the stress-strain curve which showed how the sample reacted to the stress, ultimately being pulled apart. Recently, the control system failed. The original OEM who provided the test platform came in to the Sunnen lab and decided it could not be fixed. “The old controller included a PC with a mix of sensor cards,” said Peter Kwentus. “The sensor cards were failing and the PC was a very old Windows machine, making the entire system un-supportable.” Sunnen’s upper management did not have funding for a complete replacement, so Kwentus looked into retrofitting just the control system, because the frame was still good. “I was able to re-use nearly all of the basic components of this machine, such as the power supply, mechanical power transmission and DC motor,” said Kwentus. The Sunnen engineer added a new off the shelf DC drive from AMC, new MTS linear position sensor, new load cell amplifier, and an electronic motion controller, the RMC75EMA1- AP2-D8 (shown in Figure 2), provided by Delta Computer Systems Inc. of Battle Ground, Washington. “We use Delta motion controllers in some of our honing machines, and I felt that an RMC could do the job in revamping our test platform,” said Kwentus. NEW SOLUTION: BEST OF BOTH WORLDS In the process, the Sunnen engineer discovered that combining a PC with a motion controller gives the best of both worlds: the PC software platform provides an easyto- use design platform supported by a wealth of software, and the motion controller provides very precise motion and the ability to acquire data in real-time. “With special software to link up the two environments, a very powerful, yet economical test and data acquisition platform is created,” said Kwentus. That critical software link in the case is Delta Computer Systems’ RMCLink, a download package that enables direct communication with any of Delta’s RMC family of motion controllers. The package includes a COM Component, .Net Assembly, and C++ Wrapper Class which all support serial RS-232 and Ethernet communications, and includes an extensive help file, full examples, and code snippets. RMCLink provides full functionality to read and write registers, read bits, and issue commands to all RMC controllers from any programming language. In Sunnen’s Test System Retrofit, the RMCLink COM Component was used in conjunction with Microsoft Excel and its embedded VBA to pull data directly out of the motion controller and drop it into a spreadsheet for analysis and display (see Figure 3). “RMCLink software gets the data out of the controller and puts it wherever you want it to go,” said Kwentus. “This was my first time using RMCLink software and I found it very easy to get the link up and going.” Delta’s support of the VBA programming environment also allowed control buttons to be added to the spreadsheet for platform Jog Up and Jog Down functions to get the test specimen loaded. A start cycle pushbutton on the same spreadsheet starts the test. Once the test is complete, the spreadsheet uploads the plot data from the RMC, and develops a plot of stress vs. strain. The data that is analyzed and reported also includes the starting position when force was encountered, the max stretch distance when the metal failed, and the highest force that was seen. After the test operation is complete, the data is analyzed, and a stress vs. strain curve is developed from the position, force, stretch amount, and the dimension of the test specimen: Stress = Actual Force/(Thickness* width of test piece) Strain =(Actual Position - Starting Position)/(length of test piece) An export button was added to save the data to a new .csv file for emailing and archiving. “Besides being able to use the RMC’s ease of motion and force control, the coolest part was that all operator intervention was done using Microsoft Excel as the HMI,” said Kwentus. PROGRAMMING THE MOTION The typical test cycle incorporates the following motion steps which were programmed using Delta’s RMCTools software (The software is provided free with the company’s motion controllers): • Retract the platen at fixed velocity. • Monitor the force reading. • Once the force reading exceeds a small amount (like 100 lbs), start recording data of position and load force. • Continue saving data and retracting at the fixed velocity until the force gets below 100 lbs. (which signifies that the metal broke) • Immediately stop the motion and the data collection. “It is important to stop as quickly as possible, because we do not want the machine to fly away once the metal breaks,” said Kwentus. TUNING THE DESIGN As with any closed-loop motion control application, programming the motion steps is followed by tuning the response of the control algorithm for smooth operation. “Tuning the motor was a breeze using RMC Tools’ Tuning Wizard,” said Kwentus. “After following the easy to use wizard prompts, I had the motor’s operation tuned and moving smoothly within minutes!” SAVING TIME AND MONEY Upgrading the physical aspects of the machine was a very smooth process. “The value of the Delta is ease of use and the ability to get a rich data set,” said Kwentus. “It took me about a day to take out the old electrical components and then half a day to get the load cells calibrated and working properly and then just about two hours to program and tune the Delta. The engineering time involved in making the upgrade was very low, and because of the Controller’s easy to use RMCLink interface, we didn’t need to buy a special control screen or any additional data acquisition hardware. All told, the Delta solution saved about two thirds of what the cost would have been if we had bought a new test platform from the original manufacturer.” Jason Palmer is with Delta Computer Systems Inc. Delta Computer Systems Inc. http://deltamotion.com/products/ software/rmclink.php
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