Powerlink Speeds Design of Tube-bending Production Cell

Called Uni-vercell, Unison’s machine (Jacksonville, FL) packs a complete end-to-end loading/end-forming/bending and vision inspection process in the space typically required for a standalone tube-bending machine. The machine exploits an articulated robot arm to manage all intervening movements and transfers.  The arm eliminates the conventional carriage of a tube-bending machine, and improves precision because it retains the part for the duration of the process — eliminating a lot of hardware in the process.

Unison’s Uni-vercell is an end-to-end loading/end-forming/bending and vision inspection machine.  It uses an articulated robot arm to manage all intervening movements and transfers.  The arm eliminates the conventional carriage of a tube-bending machine, eliminating a lot of hardware.

The Powerlink system, which is based on the NextMove e100 machine controller from Baldor Electric Co., Ft. Smith, Ark., handles the tube-bending and end-forming processes, as well as general operational control of the cell.  This controller manages four MicroFlex e100 servo motor drives which control the tube bending head’s clamp, pressure die and bend arm axes, plus the actuation of the end forming tool for flaring and compressing functions.  In addition, the controller manages all of the cell’s I/O plus the link to the front end user interface.

A compact footprint was a key design objective for the new cell, and Unison believes the simple daisy-chained nature of the high speed network reduced the electrical system’s size — and the wiring and system building tasks — by probably 50% compared with conventional analog motion control.

For this project, the 100 Mbps network has the bandwidth to dynamically control each motor’s position and torque parameters, which lets the robot arm create smooth and accurate bends.  The network also made it easy to deploy all the local I/O required for the cell.  Some I/O resides directly on the controller.  Other I/O is located on the distributed servo drives. The cost of this remote I/O was reduced as the Powerlink standard is compatible with the CANopen profile, allowing the use of readily available CANopen I/O modules.

This cell is designed for the repetitive production of mass volume parts such as automotive fuel, water or hydraulic components.  There is no front end user interface on the system.  It resides on a laptop connected to the cell’s NextMove e100 controller.  Unison also expects the cell concept to appeal to more general metalworking fabrication companies who manufacture in smaller batches, where a local man-machine interface will be required.  Using a standard Powerlink gateway device, the cell can be connected to a PC or conventional Ethernet network easily.  Another expansion possibility is more motion control axes, for more complex end forming for example, or labeling and marking. 

Most conventional motion controllers handle only a discrete number of axes. With Powerlink, the number of axes — and other network-located functions such as I/O — is almost unlimited.  This flexibility allows Unison to quickly adapt the machine for future applications.

Ethernet-compatible Powerlink motion and machine control hardware controls four axes of
motion plus the I/O needed for the continuous process operation.  It handles the tube-bending and end-forming processes, as well as general operational control of the cell.

The versatile machine control development system called Mint was another reason Unison chose Powerlink.  This high level language is similar in style to BASIC, but with advanced structured programming features, multitasking support, and a large library of ‘keywords’ that provide ready-to-use code for common motion control functions.  Using Mint, Unison engineers wrote the software for the entire cell in two weeks.  

The Uni-vercell can fabricate parts to an overall accuracy of 0.1 mm.  Although the cell handles repetitive volume applications, the flexibility of the robot arm allows it to be configured easily for batch production as well.  In addition, there is no drift in its motions.

The machine typically consumes around 1.5 kW of energy as measured using an example part with three bends and one end form, including stacking at the end of the process, and 100% inspection. Thus, daily electricity running costs are around 7 Euros.

The machine also delivers other technical advantages, including greater control over the bending process.  Fine adjustments to torque levels or movement profiles can be made, for example, to tailor bend quality.  Complicated shapes that might be difficult to make on a conventional hydraulic machine are easily produced because the machine can make intervening adjustments or moves between stages, to avoid a collision for instance. 

To program bends and end forms requires only the input of data such as position, angle, rotation and torque, and the machine sets up automatically.  All of the robot’s intervening movements can be programmed by simply positioning the arm manually and capturing the data.  Using these simple techniques, a complete cell program can easily be produced in less than an hour.