At parts assembly production sites, where parts are picked from stock, it is almost inevitable that picking mistakes will occur. As parts become more complex and their component types increase, the problem of picking mistakes grows. With Mitsubishi Electric’s Guided Operator Solutions, such mistakes can be easily eliminated, helping to reduce waste, improve quality and boost productivity.

A Lean Strategy in Human Mistake Prevention – POKA YOKE

Poka Yoke is the Japanese term used for mistake prevention. Statistically, it has been found that human error when picking parts is one of the most significant causes of mistakes in assembly operations. Typical problems include picking the wrong parts with a similar shape or name, picking and assembling parts out of sequence, or simply missing a part of a sequence.

While product inspection can prevent faulty goods being shipped to customers, it does little to prevent those defects from being introduced into the product in the first place. While for some companies a certain level of waste or rework will be accepted, for others there will be the desire to eliminate mistakes earlier in the production process before the real value has been added to the product.

To solve these issues Mitsubishi Electric have developed their integrated Guided Operator Solutions, based on the principles of Poka Yoke, a Japanese term that translates generally as ‘mistake prevention’. Poka Yoke is a method of eliminating mistakes in a manufacturing or logistics operation at the source before they can occur.

Tangible Benefits

The costly impact of quality issues is largely recognised for manufacturing companies that engage in assembly tasks. Mitsubishi Electric’s Guided Operator Solutions not only significantly reduce the risk of these quality issues occurring but they also can be deployed in a diverse range of industry sectors where the benefits can be identified by both managers and operators.

In a typical application, where personnel are required to pick a number of different parts or products from bins in sequence, the chances of the worker correctly picking the parts with 100 % reliability every time are small. At the very least, a significant proportion of the production time will be taken up by looking for the right part and ensuring that it is indeed the correct part number. In the worst case, a mistake introduced into the product will go unnoticed until further up the production line – if at all.

However, with the Mitsubishi Electric Guided Operator Solutions in place, the automation system guides the worker to the correct parts bin, perhaps by simply lighting an indicator next to the correct picking location, or by opening a shutter and requiring an operator acknowledgement of the successful pick of the correct part. Picking becomes not only inherently more reliable and mistake- free but also much faster, so both quality and overall productivity improve.

Totally Integrated Solution

Simple

The design of the Guided Operator Solutions has been based on simplistic concepts. Terminals are easily installed on pipe racking and connected via a dedicated cable that avoids the need to run multiple cables back to the main controller, significantly saving on wiring costs.

Intuitive connectors also enable fast installation of networks without the need to cut or strip the wires. Terminals are quickly set up with an address writer and using a dedicated software they can be directly mapped to the controller. This allows the applications to be easily configured, programmed and maintained.

Versatile

The sheer variety of the terminals available makes Mitsubishi Electric’s solution suitable for almost any application. For example, photoelectric sensors provide options for applications where high picking speed is a necessity. Alternatively, for more cost-sensitive applications an array of a push button and lever type feedback actuators can be provided.

Terminals with opening/closing doors provide a physical barrier to selecting the wrong part, a highly effective method to eliminate mistakes. Additionally, some devices are fitted with a display to identify how many pieces should be picked from any bin, again increasing operator effectiveness.

Integrated

Often assembly tasks must fit into the wider operational environment of the plant. This is essential to avoid the issues of over and under production. It is also important to consider the resource planning for parts used in the picking operations.

To permit connectivity to multiple picking applications within the plant dedicated bridges connect stations over CC-Link and CC-Link IE networks. High-speed data communication enables synchronisation of tasks, but also allows assembly cells to be distributed according to the needs of the production site. Furthermore, direct integration of MES technology permits the Guided Operator Solutions to be connected to high-level organisational systems so that output and resource planning are controlled in real time.

Expandable

At the heart of the Guided Operator, Solutions are Mitsubishi Electric controllers with dedicated masters communicating with the network of terminals. Depending on the complexity of the application, simple control can be provided using FX series PLCs or for more advanced applications the L series or Q series PLCs can be configured.

Through connecting other devices to the controller such as barcode scanners, electric screwdrivers or vision systems, Guided Operator Solutions can be tuned to the exact needs of the operator. Further enhancements can be achieved through the selection of Mitsubishi Electric’s intuitive GOT HMIs to display work instructions or alternatively drive and robotic technology can be integrated into the manufacturing cell.

Typical Applications

Guided Operator Solutions, sometimes known as pick-to-light solutions, were originally deployed in the automotive sector. However, with Mitsubishi Electric’s wide array of ergonomically designed terminals, it is possible to deploy these solutions in many other industry areas that include; logistics, semiconductor and life science sectors.

Picking

Picking is a key area where production efficiency can be improved and where product quality can be enhanced. Guided Operator Solutions significantly reduce overall man-hours, eliminate mistakes in parts picking, and also reduce operator fatigue.

Parts Replenishment

Parts replenishment is another area where mistakes can occur, and these can have knock-on effects on quality control in assembly. Guided Operator Solutions identify exactly where parts need to be replenished and ensure that correct parts are added to the bin.

Production Cell

The ‘cell production’ model for assembly is becoming common at plants focused on ‘high mix, low volume’ production, with a single operator responsible for the complete assembly of a product. Guided Operator Solutions can eliminate mistakes at source reducing the risk of re-work on the product.

Kitting

Kitting out a tray with components for a subsequent manufacturing process requires an operator to pick a number of parts from a number of different bins, following detailed work instructions for components and quantities. Guided Operator Solutions ensure the right components are added to the kit box in the right quantities, saving time and reducing mistakes.