Upside-down design and automation resolve age-old precision grinding challenges
As automation technology enables machinery to advance into ever-greater precision in ever-smaller product runs, automated manufacturing of "lot size one" is increasingly in demand. "Centerless grinding" technology, a special technique for precision grinding of cylindrical machine parts, is one example where these manufacturers’ demands can be at their greatest. Based in Beamsville, Ontario, Canada, Echo Hill Automation has more than 20 years of experience in grinding technologies, rapidly moving past the time when machining of precision parts required tremendous manual skills to manufacture components to very demanding specifications.
Today, many precision parts are first worked on in primary machining processes, such as with a lathe; then they are finished to a precise size with a grinder. Centerless grinding machines, such as those from Echo Hill, use high-performance grinding wheels to finish components at the highest levels of tolerance required to the micron level. Centerless grinding applications run the gamut from automotive component manufacturing to the machining of aerospace parts, with the highest tolerance demands imaginable.
Automated grinding challenges
Most grinders on the market can only grind one part at a time with acceptable quality and efficiency. Because of variations in fixturing (holding of parts), there must also be updates to the grinding profiles for all parts to be precisely machined. Until recently, most of these updates were manually entered, with a computer aided manufacturing (CAM) profile or a computer numerical control (CNC) dresser. Machine operators had to type in micron-level increments just to grind parts to the correct size and precision.
Another notable shortfall in centerless grinding industry-wide has been in the gauging of parts. To address this and create a competitive advantage, Echo Hill has spent considerable research and development (R&D) effort to improve the gauging technology on the company’s machinery. "Complicating matters, customers often have a wide range of different parts so they demand short production runs and frequent product changeovers," said Harry Schellenberg, president, Echo Hill Automation. These demands required Echo Hill to make its centerless grinding systems even more flexible to accommodate innumerable part sizes and dimensions.
Grinding machine performs a spectacular 180
Over the years, tolerances have become much tighter for machined parts to increase reliability during end use. Also, manufacturers today typically demand "zero defect" production, which puts more demand on machine builders to eliminate production defects and waste. Today, highly specialized machinists are fewer and farther between, which puts more responsibility on machine builders and the automation system to craft high-precision parts without defects.
Grinding heads for these types of machines weigh upwards of 1000 lb, so with repeated movement, intense wear points could develop in the sliding mechanisms and ball screw that drive machine components back and forth. In addition to mechanical wear and tear, grinding applications are notoriously dirty as grime and fluids from machining processes are difficult to manage. In many machines, coolant is sprayed continuously on ball screw housings and sliding mechanisms. Over time, these factors make it increasingly difficult to meet tight tolerances even with highly precise grinders.
In 2009, after years of intensive R&D efforts in all areas of machine and controls design, Echo Hill arrived at its innovative solution to these challenges in its new Tactic 8 machine with an 8-in.-wide grinding wheel. The Tactic 8 design flips the moving equipment "upside down" by using highly precise linear motors mounted at the top of the machine. Instead of having the spindle carriage underneath the grinding wheels, Echo Hill instead mounts them above the grinding wheels. Echo Hill has coined this patented new way of thinking, "Powered From Above."
Minimizing wear and tear, the linear motors’ magnetic attraction counteracts the weight of the slides, essentially neutralizing the weight on the recirculating roller slide mechanisms, which dramatically increases their life. The equipment and mechanisms also are kept clean because they are suspended above the process. Gravity prevents contact from most grime and coolant used in grinding.
Streamlined control architecture
In addition to mechanical advancements, the new Tactic 8 from Echo Hill also successfully reduced the number of different control platforms used to increase overall efficiency.
Echo Hill initially looked at new automation in 2008 for "control of robots used to load parts into the grinding machines," Harry Schellenberg said. "Up to that point, we had separate controllers for the machine, robots, and another to control gauge data-this required complex communication among all controllers. Echo Hill found a competitive advantage by designing a platform that could handle the robotics, gauging, and machine automation in one controller, one software platform, and one network, representing a turnkey package for us."
To achieve this, Echo Hill uses an industrial PC (IPC) equipped with a 2nd Generation Intel Core i3 processor (2.2 GHz, 2 cores) that runs a unified software platform for full machine control, including robotic and measurement systems. The IPC is completely solid-state with no rotating parts by using CFast [a CompactFlash variant for serial ATA bus] cards for the boot and storage media. In addition, an external heat sink on the IPC safely dissipates heat out of the side of the control cabinet, eliminating the need for a fan. Connected to the IPC on the other side of the pole-mounted control cabinet is an economy control panel for machine visualization.
For human machine interface (HMI) software, Echo Hill uses a different vendor.
"Running the HMI software on the same … IPC that runs our automation software is a significant improvement as well," said Dan Schellenberg, vice president and controls expert at Echo Hill Automation (and Harry Schellenberg’s brother and business partner). "Prior to standardizing on PC-based control, we used a hardware PLC and a separate ‘white box’ PC that ran the HMI. Communication between these two systems added complexity and reduced the overall performance of the control system. However, these problems are in the past."
There were numerous benefits of using the IPC as the robot controller, including reductions in cost, panel space, and system complexity. Echo Hill controls the grinding cell, each with three robots per cell, with IPC running the unified control software.
"Implementing all robot coordination … while handling 3 axes of interpolated motion for our grinding wheels with one controller and one software represents a game-changing system with fewer obstacles to implement leading-edge performance," Dan Schellenberg said. "Also, by running G code in a PC-based control platform to perform complex motion, I can more easily rewrite the programs when the parameters change. We have the flexibility to use multiple programming languages, from standard to highly specialized ones, depending on which is best suited for a particular task in one standard, unified programming environment. Simpler motion control elements are frequently handled using … function block libraries, which saves programming time."
Another software solution is used to read and write part parameters in a standard format. "This is especially helpful because in some Echo Hill applications, there may be as many as 4,000 part parameters that continuously change during production," Dan Schellenberg said. "This gives us much more flexibility to transfer parameters from machine to machine."
In addition to the highest possible precision, Echo Hill implements complete inspection of parts from the start of grinding to the final processes. With better gauge data, Echo Hill can more easily correct dressing patterns during production with the closed loop system, creating the possibility for automatic changes at micron and sub-micron levels. The machine also successfully runs four parts at a time without sacrificing efficiency.
"Within a few minutes, our customers can simultaneously grind four parts that are all ‘on the mean’—which is the pinnacle of grinding," Dan Schellenberg said. "Our customers noticed this right away-it was possible to replace four competitor machines with just one Echo Hill machine."
Industrial Ethernet (the EtherCAT protocol) is used extensively for machine networking, and a wide range of EtherCAT I/O is deployed for complete data acquisition, temperature monitoring, and vibration analysis on the grinding machines. The 2-channel digital input terminals have oversampling capabilities built in so they can acquire the fast binary control signals from the process level and transmit them, in an electrically isolated form, to the controller. The time base of the terminals can be synchronized precisely with other EtherCAT devices via distributed clocks. This procedure enables the temporal resolution of the digital input signals to be increased to "n" times the bus cycle time.
To best ensure the safety of machine operators and plant personnel, Safety over EtherCAT functionality enables comprehensive machine safety for the Tactic 8. Rather than having to run a separate set of cables to a dedicated safety controller with its own software and network, TwinSAFE integrates safety technology into the standard EtherCAT I/O system. This has made it easier and more cost-effective for Echo Hill to ensure machine operator safety during part loading and maintenance.
EtherCAT is also used to connect the automation equipment to the vision system. Echo Hill transmits data with length and diameter parameters to the vision system over EtherCAT so that it is easier to reconfigure the machine during changeover. The new gauging system in the Tactic 8 can handle the widest possible variety of parts with incredibly tight tolerances, down to 6 microns. The newly designed machines in the field have processed more than 100 million high-precision parts for numerous Echo Hill customers.
Gauging a series of successes
While the ability to machine four parts at a time is perhaps the biggest selling point for Echo Hill, the additional measurement functionality has been a big contributor to the success of the Tactic 8. After transitioning to EtherCAT and I/O terminal technology for our gauging systems, "Echo Hill successfully hit 4,000 scans per second, leaving the previous 1,000 scan limit far behind," Harry Schellenberg said.
The high performance of EtherCAT-enabled oversampling and distributed clocks is really what pushes the Tactic 8 into advanced automation territory, in addition to the full control of the robot via the main machine controller, Harry Schellenberg said.
While the new Tactic 8 system has enabled Echo Hill to quadruple the throughput of conventional grinding technology, it did not cause the controls cost to increase.
"In fact, running the kinematic systems on a central IPC that also handles all our other machine functions helped us reduce overall controller cost by over 50%," Dan Schellenberg added. "We went from four hardware controllers to just one using the PC- and EtherCAT-based system…. This has also made a dramatic impact toward reducing our cabinet space, overall machine footprint, and system complexity."
The hardware savings alone are impressive, but they are joined by savings in programming time due to the centralized control architecture.
"In the past, Echo Hill utilized servo drives with built-in intelligence," Dan Schellenberg recalled. "When we had to make programming changes, we had to perform the updates at each drive. Today, we can do all our motion software updates in one reliable spot on the IPCs. We’ve gone from days’ worth of drives commissioning time on our machine down to hours."
Faster changeovers, less wear
These benefits are not limited to Echo Hill; they also spread to the company’s end-user customers. A large percentage of Echo Hill’s high-volume applications involve grinding parts that go into automotive transmissions. This is the case for one of its customers, a transmission original equipment manufacturer (OEM) that uses Echo Hill machines to make a wide range of high-precision auto parts in very low volumes, Dan Schellenberg said.
"This requires constant changes to machine parameters to grind the different parts. The grinding wheel must then be changed, which is typically a time-consuming process. Tactic 8 changeovers can happen very quickly by changing positions on the blade to run a completely different part with minimal downtime. As evidence, their changeover time was reduced by an impressive 50% and wear and tear on the grinding equipment was also minimized," Dan Schellenberg said.
So while a master mechanical craftsman may be fairly difficult to locate today, Echo Hill Automation has the centerless grinding machinery available to expertly make one perfect, custom part just as easily as it handles high-volume production.
– Shane Novacek is marketing communication manager, Beckhoff Automation. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, email@example.com.
www.controleng.com/archives under August has more information and 7 more photos with the posted version of this article.
- Machinery redesign increases throughput more than four times.
- Controller costs and changeover time were decreased more than half with less machine wear.
- Drive commissioning fell from two days to hours.
Is it time for a machine redesign using advanced automation?
See a 44-second YouTube video from Echo Hill, showing a Tactic 8 machine in action.