Automaker changes gears without changing grippers
When a major automaker sought a new strategy for automated transmission operations, an original equipment manufacturer put electric grippers at the cutting edge to eliminate costly changeovers.
To meet the imperatives of global manufacturing agility, one of the world’s largest automakers recently tapped Moore Controls, Dexter, Mich., to provide a new material handling system to serve automated transmission manufacturing, to transport workpieces through various manufacturing cells, starting with turning steel blanks into finished gears for further assembly.
In meeting the need to handle several parts without mix-ups or errors, and to do so without costly downtime associated with changeovers, Moore designed an innovative, cost-effective solution that incorporates servo-based electric grippers to achieve the flexibility and accuracy that would have been much more costly and highly impractical using any other method.
Challenge of flexibility
“Traditional gear-handling systems focused on long runs of a single part,” said Steve Moore, president of Moore Controls. “Changeover was time consuming, labor intensive, and impacted overall throughput. The demands of today’s global marketplace require the automaker to seek a system with the flexibility to handle a greater number of parts, but without the extra tooling and changeover time of a traditional hard automation system.”
The new-generation solution needed to be adaptable to diverse applications across production lines as well as various plant installations worldwide, where levels of automation and manual labor vary. Therefore, an early goal was to employ off-the-shelf products and systems that could be maintained globally.
While several technologies and components would be part of the full system, finding the right grippers was an immediate, critical challenge. The grippers needed to be multi-purpose for picking and transporting multiple parts. The gripping system had to verify that the right part was being used. The grippers had to handle 10 sizes of gears measuring between 30 mm and 50 mm, with variances between them as low as 0.5 mm. To achieve high productivity, the traditional solution of changing grippers to handle each new gear size was not an option; one gripping solution had to do it all.
Electric grippers end changeovers
To meet the most critical challenge of picking and measuring the right part, Moore selected a gripper model from the automaker’s preferred supplier. The parallel, two-fingered grippers use a 24 V dc motor with an encoder designed for electrical controls.
The grippers are variously mounted on gantries, robots, and modular frames that can be adapted for each manufacturing cell. A minimum of two gripper assemblies is used for each modular cell, and some units have up to five grippers; a full material handling line of integrated, automated stations uses hundreds of grippers. (See more below about Moore’s flexible automation system.)
In the most common application involving these stations, or what Moore calls “flexible automation cells,” the grippers are mounted to standard pneumatic components: ISO cylinders for horizontal and vertical part rotation; valve terminals; and air-preparation components. Two sets of grippers are mounted on the pneumatic cylinders. They are oriented 90 degrees from one another so that as one gripper clamps down on a gear’s outside diameter (O.D.), the other swivels into place, ready to pick the next gear for more constant, productive operation. As the grippers clamp onto the O.D. of each gear, they precisely measure the diameter of the gear, and reject any that are the wrong size and may have been introduced during loading by manual operators.
To measure and identify each gear based on encoder feedback, the grippers use electric controls with servomotors and ball screws managed by programmable logic controllers (PLCs). This is accomplished at each cell by a motor controller that communicates directly to a PLC via Profibus network using the ProfiSafe machine safety protocol. The PLC calculates the absolute position of the gripper fingers and sends direct commands to grip and measure each part.
This control strategy has the technical benefit of not relying on analog signals or digital proximity sensors for feedback. Specifically, this strategy provides full, closed-loop servo control and actual encoder feedback delivering “infinite positioning possibilities.” The overall solution, a hybrid of electromechanical grippers supported by pneumatic components, is unified in its use of standard control components. In addition to the above, these components also include a modular I/O system, designed for fieldbus networking with electrical and pneumatic controls, and an I/O valve terminal interface.
Moore Controls’ application of electric grippers in tandem with pneumatics in unified control architectures:
- Integrates well with other equipment as well as manual operations
- Provides quality control, defect rejection, and productivity through precise measurement and control through integration with the grippers
- Eliminates the risk of human error in a semi-automated environment to prevent potentially costly equipment damage and downtime
- Provides unparalleled flexibility, eliminating a major source of downtime. One set of grippers now handles 10 gears due to the travel of the fingers, the design geometry, and the controls strategy’s capabilities
- Builds on the strengths and efficiencies of electric and pneumatic actuation and control.
In the area of flexibility, the overall solution contrasts starkly with a conventional gripper strategy that would have consumed an hour or more to change gripper fingers at each cell, across all cells, each time a different gear was to be manufactured.
“The flexibility of the system, from its inherent design to the specific components chosen, provides a lower cost automation solution than the automaker was accustomed to in their gear manufacturing process,” Moore said. A side benefit of Moore Controls’ first use of electric grippers is that the OEM’s team gained additional exposure to new control strategies, which “may open up new ideas for other applications, other types of machines that we design and build. For me, that’s important; it broadens the horizons for our engineers.”
Global shipments begin
During 2012, Moore Controls completed designs on 59 flexible automation cells. Eighteen are for a facility in France, which provides transmissions for the European market. The remaining 41 are bound for China, where a facility is being expanded to produce all of the customer’s transmissions for the Asia-Pacific market.
The first two units shipped to France in August 2012 and are now being integrated into a new line. China will get its first shipment in the first quarter of 2013. All 59 automated cells are targeted for completion by the second quarter of 2013.
The automaker has been satisfied with results, according to a distributor involved. Moore added that the project has led to “quite a bit” of growth and exposed his company to a broader network of machine tool builders that may lead to further new business opportunities.
Flexible automation system
Working in partnership with the automaker, Moore Controls developed a flexible automation system design based on modular cells that can be assembled into lines at each designated plant. The design consists of a frame onto which specific mechanical, pneumatic, and electrical components are mounted to load and unload parts in each step in the gear manufacturing process.
The system accommodates a mix of automated and manual operations, from integration with pallet conveyors to automated tooling.
Typically, operators load workpieces from trays onto sword-like rods or “skewers.” These are, in turn, loaded onto pallet conveyors to create in-feed part buffers. The skewers, fitted into 300 mm x 500 mm aluminum plates, travel into the automated cell. There, grippers pick and position each workpiece into an automatic machining cell using either a two-axis pick-and-place gantry or six-axis robot. Exiting parts are placed into buffers on the pallet conveyor skewers.
Operators then manually place the machined workpieces back onto the conveyor for the next machining process. The first process is hobbing, where gear teeth are cut from the O.D. of a steel blank. This is followed by subsequent processes (and flexible automation cells) for grinding, honing of the inside diameter, and more than a half-dozen additional actions through to the completion of finished gears.
– Bryan Morehouse is automotive industry project engineer, Festo. Edited by Mark T. Hoske, content manager, CFE Media, Control Engineering, Plant Engineering, and Consulting-Specifying Engineer, firstname.lastname@example.org.
- Automotive material handling applies automation
- Servo-based electric grippers provide flexibility, accuracy
- Machine safety communication protocol helps
What new automation technologies can be applied in your next flexible automation cell?
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