The latest project from the partnership of TM Robotics, Toshiba Machine and systems integrator Evershed Robotics has demonstrated the speed and accuracy that can be gained by using robotics in the metal fabrication process.
The three companies have developed a system that machines lockable fasteners for car panels. It comprises four twin drill heads arranged on either side of a TM SR-504-HSP SCARA robot. Evershed Robotics designed the system so that one to four drills can be employed in a series, according to throughput requirements. At full output, the machine is capable of producing a finished fastener every four seconds.
Evershed Robotics Ltd designed the machine to a specification it was given by the end user. This was simply that the current range of fasteners being produced needed to be expanded, and that the existing machines didn’t have the capacity to achieve the targets that were being set. In fact, in some cases machines simply didn’t exist to produce the fasteners that were now required. Before the Evershed system was introduced, each fastener in the range was manufactured on a dedicated machine; this meant that the potential for failure and thus downtime was vastly greater. As a consequence, the new system has improved quality and reliability, but above all it has allowed a range of fasteners to be manufactured that simply couldn’t be produced previously.
The robot can handle up to 15 different fastener types, measuring between 9.5mm and 50mm in length. The fasteners are introduced to the drilling area from a vibratory feed bowl, via an escapement mechanism that presents them in approximate orientation. Working in conjunction with a recognition system, the TM SCARA robot picks the fastener up and then performs extremely fast, accurate, correctly orientated placements to any one of the free drill heads. Once the fasteners have been machined, they are automatically ejected into the output tray.
The robot controller is linked with the control of the feeder system and the drill heads via handshake, digital I/O signals. That is to say that the robot sends a signal, or a ‘handshake’ to the drill to say when it is out of the way and the next element of the process can begin.
Programming can be accomplished either off line or at a machine; alternatively, the robot can be programmed via a PC using SRPC software. The entire system can be reset in just five minutes and typical batch sizes are between 10,000 and 250,000.
With its very high-speed 4-axis capability, the TM SCARA ideally suits such pick and place functions. The robot’s SR7000series controller gives it the ability to track and then pick an object from a moving conveyor, or receive input from a recognition device. It can then quickly transfer it to the target position with repeatability accuracy of ±0.02mm.
Toshiba’s SCARA robots, distributed in the UK by TM Robotics, have arm reaches ranging between 424mm and 1054mm. Also in the SR series is the SR-654HSP, which has achieved record-breaking traversing rates of 600mm in 0.93 seconds, and even with a 5kg payload, the robot achieved the same distance in just 1.16 seconds. The reinforced arm can handle up to 20kg at half speed, or 10kg at full speed.
The SR700 robot controller is capable of simultaneously processing input and output signals during robot motion. Therefore no time is wasted waiting for signal processing to be completed. The controller uses absolute encoder feedback rather than incremental signals, thereby eliminating the need to implement a zero return on start up following a shut down.
There are options for PTP, short cut, linear interpolation and circular interpolation motion modes. With a total memory capacity of 6,400 points (12,800 steps), the controller also offers a multitask function, allowing a maximum of four tasks to be handled at any time. The mechanical movements of the SCARA robots are controlled using Toshiba’s own revolutionary digital servomotors, amplifiers and motion controllers.