Automated component inspection system provides fast product changeover for production flexibility

Citation

(2005), "Automated component inspection system provides fast product changeover for production flexibility", Assembly Automation, Vol. 25 No. 4. https://doi.org/10.1108/aa.2005.03325daf.004

Automated component inspection system provides fast product changeover for production flexibility

Automated component inspection system provides fast product changeover for production flexibility

Keywords: Inspection, Image sensors, Flexible manufacturing systems

1. 1.

   Innovative bowl feeder uses Festo Checkbox imaging system to maximise production flexibility.

2. 2.

   Ten minutes product changeover – compared with up to 8 h on other lines – enables insert manufacturer to embrace small batch size production strategy.

Specialist parts handling company RNA Automation has developed a machine based on the Festo Checkbox vision inspection system to verify the quality of small component parts A key benefit of the new machine is that it enables the inspection process to be switched very quickly from one type of component to another, with minimal disruption to production.

RNA Automation is a leading supplier of parts handling machinery for manufacturing applications. It specialises in the development of turnkey systems for orienting, feeding and conveying small components, to help parts manufacturers streamline their production processes (Plate 3). According to Andy Perks, Sales Manager for RNA Automation, “We already produce systems with integrated vision inspection facilities, but for this particular application we wanted a camera system that combined fast throughput capabilities with a high degree of product changeover flexibility. After surveying the market we realised that the Festo Checkbox system had exactly the right performance attributes. We were particularly impressed with its control software, which uses a learn mode to minimise programming and allows part changeovers to be accomplished very quickly and easily. As a consequence, we intend using Checkbox as the core technology for our latest-generation intelligent parts inspection machines”.

Plate 3 Tappex produces a wide range of brass and steel threaded inserts and fasteners, which are manufactured to very tight dimensional tolerances

The first user of the new machine is Tappex Thread inserts Ltd. This company designs and manufactures an exceptionally wide range of brass and steel threaded inserts and fasteners for use in plastics, structural foam, composite materials, wood and metal. These small components are manufactured to very tight dimensional tolerances, and Tappex has built up an enviable reputation for the quality and consistency of its products by applying rigorous process control and post-production inspection procedures.

The quality control department at Tappex's main UK manufacturing facility in Stratford-upon-Avon uses a combination of visual and automated inspection systems to verify that manufactured parts are within specification, depending upon the type of insert. The company wanted a new vision inspection system primarily for inspecting inserts that will be fitted by robotic assembly systems, as these tend to be particularly sensitive to tolerances and can jam if their feed components are not perfect. Until now, it has relied mainly on visual inspection and conventional measurement equipment for these parts, which is obviously time- consuming and can never be 100 per cent accurate. And although Tappex already uses automated vision inspection for some product lines, it can take up to 8 h to reconfigure the system to inspect a different part. As the company wanted to inspect some inserts in batch sizes as low as 10,000, perhaps switching parts up to three times a day, its existing system did not provide the flexibility needed for this application.

The new component inspection machine includes a vibratory bowl feeder, a Festo Checkbox vision system – comprising an integrated camera/conveyor and control unit – and a number of air jets and solenoid valves, all mounted on a worktop height plinth. The conveyor and inspection chamber – which contains the Checkbox line scanning camera and a laser target illuminator – are supplied to RNA Automation as a fully- assembled unit, with all control electronics housed in the separate enclosure.

The inserts to be inspected are loaded into the vibratory bowl feeder and progressively “climb” to the top along a spiral track; a baffle plate encourages longitudinal settlement. At the top of the bowl, an air jet blows any inserts that are still standing vertically onto their sides, and a gating gauge on the rim then ensures that all inserts are queued up end-to-end, with any that are out of line falling back into the bowl. At this stage, as it exits the bowl feeder, the front-most insert is pushed onto the Checkbox conveyor belt by the other inserts in the queue. The belt is driven at a constant speed that is higher than the feed rate of the bowl feeder, using a brushless DC servomotor and an encoder to provide positional feedback data to the control unit. As each insert lands on the belt, it accelerates away from the one immediately behind it, ensuring there is always a gap between components presented for inspection. For this application, the throughput is normally about 120/180 inserts per minute, although the conveyor belt's speed potential of up to 800 mm per second provides considerable scope for higher productivity applications.

The imaging system can check up to 12 separate parameters: length, height, circumference and cross-sectional area are measured to within 0.1 mm, and by counting the number of pixels to the right, left, top and bottom of the insert's centre point, the system can also verify shape conformance and other critical factors such as thread pitch and chamfer angles. After inspection, each insert is categorised as 100 per cent good or of unknown quality. It says much for the quality of Tappex's production processes that 99 per cent of inserts that “fail” inspection are not defective – they were either incorrectly oriented or too close to the camera for thorough inspection, or the inspection result was ambiguous which is typically caused by two small inserts being presented end-to-end without a gap between them.

The software that comes with the Checkbox includes a key tool known as CheckKon, which enables users to download different programs, edit inspection parameters and display an analysis of the most recently scanned insert, as well as providing a “learn” function that allows the system to be taught about new components through automated inspection rather than discrete programming. If the standard teach-in process is unable to resolve very small component details, a tool known as CheckQpti can be used to optimise the component recognition process.

Although the system has a facility for automatically returning any incorrectly oriented components to the bowl feeder, this is not currently used by Tappex, who prefer to return all “failing” parts to the bowl for second pass inspection at the end of a batch. The company also operates the system on a fail safe basis, in as much as all inserts exiting the inspection chamber are conveyed to the “reject” chute; only those that have passed ail quality checks are blown off the conveyor belt and directed to the packaging area, by a pulse of air from a nozzle located in the body of the conveyor The air jet is controlled by a solenoid valve driven by the control unit. As a point of interest, Festo had to develop special valves for Checkbox imaging applications; most conventional valves have a response time of around 12ms, which would be inadequate for controlling an air jet intended to accurately hit a small component travelling at up to 800 mm/s. The high speed valves have a response time of just 1 ms.

The system was installed at Tappex's manufacturing facility last year, and has performed flawlessly ever since. The company is extremely pleased with its performance, and particularly likes the fact that the system can be reconfigured to inspect a different type of insert simply by adjusting the air jet and gating gauge on the bowl feeder, and selecting a different inspection program on the control unit. Tappex has also found that the software supplied with the system is highly intuitive and easy to use; the entire changeover process can be accomplished in about 10min, and customers can be supplied with 100 per cent fully qualified parts.

For further information please contact: Nicoia Meadway, Festo Ltd, Technology House, 1 Fteetwood Park, Barley-Way, Fleet, Hampshire GU15 2QX, Tel.: 01252 775000; Fax: 01252 775001; web site: www.festo.com; E-mail: nicola-meadway@festo.com

Contact: RNA Automation Ltd, Hayward industrial Park, Tameside Drive, Castle Bromwich, Birmingham B35 7AG, Tel: 0121 749 2566; Fax: 0121 749 6217; web site: www.rna-uk.com; E-mail: enquiries@rna-uk.com