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Should you turn to robots? Stirling Paatz of robot integrators, Barr & Paatz, considers the viability of paintshop automation.

Spray painting is regarded as one of the core applications for industrial robots and, in the early days, the technology was enthusiastically adopted by major automotive facilities, then their first-tier suppliers. At that time, the hostile nature of the sprayshop environment made it a prime candidate for flexible automation, which would remove human operators from the process altogether and consequently avoid some of the costly health & safety measures being implemented, at the same time making significant gains in quality and throughput.

With those early hydraulic robots, the technological focus was on robustness and reliability, looking to improve machine uptime and reduce maintenance requirements, and increasing numbers of automotive plants applied robotics for painting vehicle interiors and exteriors, as featured in many documentaries and commercials. By the mid-80's, the first electronic robots were introduced, bringing faster performance, increased flexibility and repeatability, and the 6-axis Articulated robot became accepted as the standard machine, offering the reality of 100% robotic paint application. A decade on, what was arguably the first application-specific 'painting robot' was introduced, with integrated paint process equipment such as colour changers on the arm and paint supply lines routed through the robot base.

[ILLUSTRATION OMITTED]

More recently, sales of industrial robots to the automotive market have tended to stagnate, with the latest figures even showing a decline in some car-making countries, but there are strong signs of growing demand from paintshops and industrial surface coatings users in the non-automotive sector, prompted by skilled labour shortages, higher quality standards, environmental regulation and the need to eliminate tedious, repetitive work. To a very considerable extent, this new generation of customers will benefit from the fact that the painting robot is now a mature, stable and highly refined product and that early development costs and technical challenges have largely been absorbed by the major machine manufacturers and those early adopters in the automotive industry.

In fact, with the price of robots falling and their relative performance increasing exponentially, it's estimated that a robot now costs less than a quarter of one bought in 1990, with similar functionality. What's more, the kinematics and features of advanced painting robots are now being combined with more compact designs and footprints, making them ideal for smaller paintshops and factories.

So, having accepted that the technology is available and the price tag is much more affordable, what factors should prompt you to consider automating your paintshop? Well, if you need to meet tight tolerances regarding film thickness and consistency of finish, then you're a candidate for robotics. Even if manual sprayers can satisfy most quality requirements, can they offer the repeatability and productivity that is increasingly demanded? Do you have competition from overseas, where laws to protect workers and the environment are less strictly applied? Is it difficult to recruit and retain skilled manual sprayers and do they have concerns about their working environment? Should any or all of these strike a chord, then robotics should be on the agenda.

Many coating contractors and industrial paint users believe that if component geometries are too complex and production batches too small, then robotics is not an option - but that is far from the case. Robots can be programmed to track the contours of the most complex components, maintaining optimum spraygun orientation and distance at all times. Parts that are manufactured and painted only once are not really suitable, but if they are painted regularly, even with major time gaps between jobs and relatively short production runs, then there's no problem. Preprogrammed software routines can be called up instantly from the robot controller menu, while efficient cartridge systems enable quick colour and paint changes without stopping production.

True, if yours is a low-volume job shop where no two painted parts are ever the same, robotics would not really be cost-effective. Otherwise, robots can handle a whole range of dissimilar parts at high throughput rates, even in small batches, and, basically, a robot can paint anything a manual sprayer can and will do so consistently, without ever tiring.

All of which brings us to the operational advantages that robot automation brings to the paintshop:

Improved quality--Drift-free trajectories and accurately controlled gun triggering provide specified film thicknesses and minimum levels of variation, with tolerances of [+ or -]0.2mm typical of robot applications, all of which contributes to enhanced quality, time and again.

Paint savings--Paint and solvent savings are in the region of 25-30%, when replacing manual spraying with robotics, as a result of increased transfer efficiency, improved trigger accuracy and keeping overspray and paint overlap to a minimum.

Increased throughput--While there is a limit to the speed at which paint and powder coatings can be applied, cycle times are considerably faster and modern robots are designed to operate for two or three 8-hour shifts a day without affecting efficiency.

Better safety--Although environmental legislation and water-borne paints have improved spraybooth conditions, robots still remove human workers from particulate-laden atmospheres and the genuine risk of RSI arising from routine, repetitive work.

Reduced rework--Robots can be programmed to apply various film thicknesses to different areas of the component, without runs or sags; even if programming errors did occur, the fault will be exactly the same each time, so technicians can easily identify the issue and take remedial action.

Operating economies--In addition to materials, further economies arise from less maintenance and cleanup, arising from reduced overspray, lower filtration costs and less emissions, while there are more savings to be gained from optimising airflow in an unmanned booth.

Equipped with the right applicator, robots can be used for applying a primer, undercoat, finish coat or clearcoat, using water-borne, solvent-based, powder, UV-cured and other coatings, in more or less exactly the same way as a manual sprayer, but without tiring or losing concentration. As to the technology, there are various robot kinematics or configurations available, the most common of which include straightforward Cartesian or Gantry types, high speed Delta robots and 4-axis SCARA machines and doubtless there are potential spray painting applications for each kind. Nevertheless, as mentioned earlier, the painting robot of choice is the Articulated or Jointed Arm robot, which has six axes or 'degrees of freedom' to control the location and orientation of the end-of-arm tooling and closely resembles the actions of the human arm and wrist.

[ILLUSTRATION OMITTED]

With a large, almost spherical working envelope, plus the capacity to reach over or around components and twist and tilt the applicator, the Articulated robot is ideal for even the most complex spray painting tasks and represents the standard configuration for dedicated painting robots. In addition to conventional floor installation, these robots can be fixed to a wall or inverted on the ceiling, saving valuable floorspace in the spraybooth and allowing the arm to access hard to reach areas; there is also the option of mounting the robot on one or more linear mechanical axes, to expand the working envelope and accommodate larger parts or track a moving conveyor in a continuous running system.

Specifying a robot for a particular paintshop is, quite frankly, a job best left to specialists like ourselves, since you need to take into account the available work area, the robot footprint, the reach required to perform identified tasks, the machine's accuracy and repeatability ratings, different wrist configurations and the target cycle time for completing a total process operation. Different manufacturers' capabilities and model range in the particular price/performance category will also have to be evaluated, together with their dedicated control software, integrated spraygun options and other ancillaries. In fact, employing advanced 3D robot simulation software, we can actually build complete robot configurations on screen, replicate the workpieces to be sprayed and run video sequences of the workcell in action, to verify that theoretical calculations would actually work in practice.

Typically, a painting robot would be rated as explosion-proof, feature a hollow arm/wrist design to enable cables and paint supply hoses to be routed internally, and be protected to IP67 to prevent the ingress of fluids and particulate, with the option of disposable covers to protect the manipulator from any overspray. Also, paint robots can be equipped with closed-loop control for paint and airflow adjustment, to ensure accurate fluid dispensing and uniform film build, and colour change valves mounted on the arm, to allow rapid paint changeovers.

In this field, payload is not a major consideration, since applicators are relatively lightweight, although other paint process equipment and supply hoses need to be included in any weight calculations. With regard to end-of-arm tooling, there is the usual range of automatic sprayguns, electrostatic guns, high speed bell atomisers and powder coating applicators, mirroring the choice of manual spray equipment, and here your expert knowledge needs to be brought into the equation, choosing from robot manufacturers' options lists or spraygun suppliers with whom you're already familiar, to suit your particular process.

There are, of course, other important aspects to consider: feeding mechanisms, such as index or continuous overhead conveyors for presenting the parts; fixtures or hooks for attaching the items to be sprayed; safety guards and interlocks for protecting people and processes; teaching pendants for lead-through programming; and HMIs (human machine interfaces) for touch-screen operation. But they are beyond the scope of this introductory article. Nevertheless, I hope that I have provided enough information to enable a serious consideration of robotics for your own paintshop. There is little doubt that where tight tolerances, optimum quality, improved throughput, operational savings and overall competitiveness are priorities, robotics technology should be on your must-have list.
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Title Annotation:ROBOTICS
Publication:Finishing
Date:Nov 1, 2009
Words:1579
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