Mitsubishi RV-6S six-axis robot feeds CNC milling machine

Robotics and industrial automation are commonly associated with capital-intensive, large-volume manufacturing, as well as high-speed repetitive processes and advanced products. Yet Brass Products, a name redolent of traditional engineering and craftsmanship, employs a comprehensive level of automation at its three-man operation near Ashford, Kent. Furthermore, in what owner Duncan Rye describes as "the most high-tech garden shed you will find," robotics specialist Barr & Paatz has just installed and commissioned one of the latest generation of Mitsubishi six-axis articulated robots for feeding a CNC milling machine, a previously tedious and potentially hazardous manual operation.

Developed specifically for handling low payloads up to 6kg, and aimed particularly at small and medium-scale enterprises, the Mitsubishi RV-6S has a precision repeatability of +/-0.02mm and working speeds of up to 9500mm/s, enabling it to complete the '12-inch test' in less than one second. Its slim, compact construction, space-saving robot controller and working radius of 695mm make this machine excellent for applications where there is restricted floorspace, such as Brass Products' 193sq-ft 'shed'.

Total reliability

Installed by Barr & Paatz, it is has impressed Duncan Rye with its 100 per cent reliability and its ability to perform pick-and-place tasks perfectly, time and time again; so much so that, with a move to rather more spacious premises scheduled shortly, he is considering another longer-arm RV-6SL, for operating in conjunction with a high-performance CNC drilling centre.

Duncan Rye says: "The installation cost is not even the equivalent of an average salary, so the robot will pay for itself within the next couple of years. Besides, it does not get bored, does not take tea breaks and does not make mistakes. In fact, it has not made a single error since the day it was installed."

Interior designers and architects, looking to enhance antique Victorian, 1920s and 1930s radiators without sacrificing performance, specify Duncan's period-style valves, such as at Islington Library, where Brass Products' fittings were the only ones suitable for the original iron pipes. With list prices starting from 150, these are clearly premium products at premium prices; even so, Duncan Rye has difficulty keeping pace with demand.

A self-taught engineer, Duncan established Brass Products around eight years ago and, from the outset, decided to invest in automation. To date, in excess of 150,000 has been spent to achieve the precision required, reduce manpower costs and deliver the extremely high standard of finish that makes his products in such demand. With only three employees, including himself, Duncan annually produces 3500 pairs of valves, complete with solid walnut handwheels, with every one polished and assembled by hand.

The application

Barr & Paatz, which specialises in process automation and is an official Mitsubishi robot integrator, was invited to recommend, configure and commission an industrial robot to replicate a labour-intensive manual routine. Brass nuts, machined and threaded from hexagonal bar stock, are loaded into a CNC milling machine by the Mitsubishi robot, which picks unfinished nuts individually from a tray, feeds them into the machine, then rotates them 60 degrees at a time until every face has been skimmed to produce a high surface finish, before returning them to the tray.

Barr & Paatz despatched its Senior Robot Engineer, Steve Gould, to Brass Products' premises in order to study the application and make recommendations based on the required throughput and geometry of the available workspace. The extremely limited operating envelope, and the need to replicate the motion of a human hand, dictated a six-axis robot configuration, with its rotating wrist joint and capacity to twist and tilt workpieces; taking into account the high-speed process, small installation footprint and modest payload, Barr & Paatz specified one of the newly-available Mitsubishi RV Series robots, which has six degrees of freedom. Exploiting its engineering heritage, Brass Products itself sourced appropriate end-of-arm tooling and manufactured the gripper fingers that hold the brass nuts, while Barr & Paatz provided specialist on-site training.

Because space is at a premium, the parts tray currently holds only sufficient stock for a 30-minute work cycle, although the robot/machine combination still manages to produce one month's supply in just three days, adapting easily to different sized nuts. The lightweight robot is mounted on an overhead gantry and, between batches, is simply swung aside to allow routine machining work.

With spacious new 2000sq-ft premises already earmarked nearby, Duncan will soon have room to handle larger batches, with a consequent increase in throughput. An additional RV-6SL robot, with a working radius of 900mm, will then be teamed with the latest Robodrill, to facilitate a second fully-automated machining system.