GROB-Werke GmbH & Co. KG creates high-volume production systems for the electric vehicle (EV) market. Based in Mindelheim, Germany, the machine tool manufacturer recently completed a sophisticated system for making hairpins, which form the stator winding rims of electric motors. The complexity of this system, which was built for a U.S.-based EV maker, illustrates the advantages of a fully integrated, optimally scalable automation system.

A globally operating family business, GROB has been developing production equipment and machine tools for automotive OEMs and their suppliers for more than 95 years. The company’s portfolio includes machining centers, production systems, manual assembly stations and fully automated assembly lines. It also includes production systems for electric motors, batteries and fuel cells.

“We cover the entire production chain and offer customer-specific systems for the entire EV powertrain,” says Fabian Glöckler, head of the control technology department in GROB’s electromobility business unit.

The hallmarks of GROB’s EV applications, including the hairpin machine, are minimum cycle times and fast process sequences. The company meets these requirements with a variety of technologies from Beckhoff Automation, including PC-based controls, EtherCAT fieldbus technology, drives and the eXtended Transport System (XTS), a fast and flexible linear-motor transport system.


Powerful Controls Energize Manufacturing

Manufacturing EV motors is much different than production of internal combustion engines, according to Daniel Gugenberger, group leader of electrical design at GROB’s electromobility business unit.

“The classic assembly processes, such as bolting, press-fitting and manual assembly operations, have been automated to a large extent and would not be able to be performed by a machine operator with the required quality, precision and speed,” he says.

This is where PC-based control from Beckhoff has proven its worth, he adds, because detailed machine and process data are of crucial importance due to the high system throughput

“When a complete manufacturing process runs in two seconds, production monitoring and error analysis are possible only with analysis tools and high-speed cameras,” he says. “We very often use the TwinCAT Scope View software oscilloscope for this.”

Around 200 hairpins in approximately 50 different designs are required to build a stator winding. These are produced one after the other in the order required for placement in the pre-insertion nest. Inline error detection is therefore important.

“In the event of a material or geometry error, the corresponding hairpin must be produced once again and inserted into the system using automated feed so that it can be inserted at the correct position,” Glöckler explains. “With the large number of motion axes and hairpin variants, this means an enormous management task for the control technology, as a wide variety of parameters, bending angles and cam plates need to be calculated just in time.”

According to Martin Ellenrieder, group manager of function development in GROB’s electromobility business unit, production of EV components has placed new demands on control technology.

“Compared to systems for internal combustion engines, systems [for EV motors] are characterized by more sophisticated stations, reduced PLC cycle times, a higher proportion of drive technology in assembly, and sophisticated coupled movements.”

This is also evident in the hairpin machine, which is fully equipped with Beckhoff control and drive technology. In addition to four GROB spindles, the system includes 57 numerically controlled axes: 40 real axes, five virtual axes and 12 XYS movers that are operated as individual servo axes. In addition, there is an extensive number of I/O, consisting of EtherCAT and TwinSAFE terminals or box modules, with 270 digital inputs and 150 digital outputs.

Using a C6030 or C6032 ultra-compact Industrial PC (IPC) and TwinCAT 3 automation software as the control core, the machine achieves a high output rate based on a cycle time of just 2.3 seconds per hairpin. This is even more impressive due to the complexity of the machining process and the number of control tasks involved, such as wire feeding, bending, stripping and positioning. The control tasks include:

  • Wire supply from a coil to straight copper wire, with or without electrical testing of wire insulation: PC-based control for the “dancer,” which feeds the wire.
  • Stripping copper wires on the fly: axis positioning, cam plates and a flying saw.
  • Wire feed: coupling of axes to a second encoder; switch-over of the encoder, depending on the system’s operating status; and switching of axes via interfaces for special operating modes, such as travel with or without wire.
  • Wire inspection: transport and positioning.
  • Press-fitting and cutting: cam plates, as well as compensation of material displacement during the pressing or cutting process via dynamic coupling factors of the virtual gear functionalities.
  • 2D bending: dynamic cam plates generated by hairpin parameters that are coupled using dynamic coupling factors of the virtual gear functionalities.
  • 3D bending: dynamic cam plates generated by hairpin parameters that are coupled to the XTS movers by dynamic coupling factors of the virtual gear functionalities.
  • Pre-insertion of the hairpins: cam plates or coordinated motion.
  • Variety of infeed variants and positioning movements of the pre-insertion nest and clamping finger: coupling of virtual and real axes.


Proven Automation and Innovative HMI

As early as 2004, GROB began to implement Beckhoff technology on its machinery, such as test stands. Then, in 2017, the company automated its first assembly line with PC-based control. “The main reasons for [using Beckhoff technology were the demands for] short control cycle times and high system flexibility for future applications,” says Ellenrieder. “[In addition, we needed] numerous interfaces to different bus systems, extensive motion functions and deep diagnostic capabilities.

“TwinCAT offers as an advantage, a special openness—for example, with the integration of Matlab, which helped especially in the development process for the systems,” he adds. “Process engineers could thus easily integrate simulations into test facilities. Further advantages include automatic code generation from the CAD system through to the HMI; the simple integration of motion control software blocks developed in-house; and the integration of version control, bug tracking and software testing. In addition, the flexibility of TwinCAT makes standardization in software development much easier for us.”

Beckhoff’s ultra-compact industrial PC, the C6030 (or the C6032, if more interfaces are required), is used in connection with a CP3918 multi-touch control panel with customer-specific push-button extensions. “The PC provides sufficient computing power to reliably achieve our target of a 4-millisecond PLC cycle time,” says Glöckler. “As an added benefit, it has a compact design and variable mounting options.”

For convenient and error-free machine operation, Grob relies on Beckhoff’s TwinCAT HMI. “Close cooperation with Beckhoff…was important at the beginning to implement such a large HMI project,” says Glöckler. “This worked very well, for example, with the automatic coupling between HMI and PLC and the implementation of multiple languages. It resulted in an HMI tailored to our requirements with a focus on intuitive usability, clear parameter display and exceptional diagnostic depth. The result is a uniform and innovative operating concept for all of our systems.”


Sophisticated Motion

The numerous rotary axes are implemented with AX5000 servo drives, EL72xx and EP72xx compact drives and AM8000 servomotors. Ellenrieder sees a particular advantage in motors and drives with Beckhoff’s One Cable Technology (OCT).

“OCT results in significantly less cabling effort and minimizes potential sources of errors,” he says. “Other important factors when using the AX5000 are the covered encoder interfaces and the safe motion functions of the AX5805 TwinSAFE option card.”

Ellenrieder also likes the rich set of functions within TwinCAT, such as TwinCAT NC point-to-point, NC camming and NC flying saw.

The rotary motion axes are supplemented by an XTS linear-motor transport system. An oval, 3-meter-long track system with 12 movers transfers individual hairpins to a linear portal for the final insertion process. According to Gugenberger, the XTS offers application advantages, particularly flexibility for adding new functions.

“In addition to classic transport tasks, we use the XTS for flexible positioning at different processing steps, such as the bending and camera stations. We benefit from the system’s compact design as well as its modularity, which makes it easy to integrate different stations,” he explains. “The transport system yields further advantages through flexible distance control according to the component status (no component, first bend, second bend); the reduction of cycle times; and the decoupling of individual processes so that, for example, varying process times do not directly affect the machine as a whole.”

According to Ellenrieder, TwinSAFE has also proven itself as a safety technology and offers a high degree of flexibility in safety applications. In addition to the drive-based safety technology, the EL6910 TwinSAFE Logic module provides a dedicated safety controller in an I/O terminal format. In complete production lines, the distributed safety devices of individual machines and systems communicate with each other via the EtherCAT Automation Protocol (EAP).

“This safety communication across control system boundaries is a very important aspect of our machine safety,” Ellenrieder says. “GROB’s customers use a large number of systems that are interlinked.”

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