Robotics Tech Papers
Five Steps Towards More Picks Per Minute
by Josef Karbassi, Vice President Automation Division
PIAB USA, Inc. Posted 05/01/2014
So, how do you make sure that your vacuum-based materials handling system is as efficient as possible, and how can such a system be optimized to pick more items per minute? This step by step guide will hopefully help.
Step 1: Decentralize your vacuum system A decentralized vacuum system with several smaller pumps close to where the vacuum is needed is preferable to a centralized system using one centrally placed pump. In a centralized system, there will be great losses due to the long, tiny hoses, bends, fittings, valves and filters, and these losses have to be compensated for by using a larger vacuum pump. Such over-capacity is not necessary in a decentralized system, in which vacuum losses are eliminated. As a result, the energy consumption can be greatly reduced, often halved, if a centralized system is replaced by a decentralized system. The energy cost aside, the physical limitations of a centralized system will always present problems. It is important to remember that a vacuum system is different from a compressed air system, which is far less sensitive to losses. Just as high voltage is used for long distance transportation of electricity and then converted to low voltage as late as possible to minimize losses, compressed air should be converted to vacuum flow as late as possible in the system.
Step 2: Use a multistage ejector Faster air evacuation of the system will increase the production rate. High initial flow will result in immediate suction and quick pick-up. Choosing an efficient multistage ejector instead of a single stage ejector can reduce the evacuation time and help to substantially speed up cycle times. State-of-the- art multistage vacuum ejectors can reach required vacuum levels up to twice as fast as single stage ejectors, with the same energy consumption Multistage vacuum ejectors in the form of a nozzle cartridge with built-in flap valves and filters are made of light-weight materials and can easily be integrated directly into suction cup fittings or the boom structure of robot end effectors. Changing or cleaning the cartridge is quick and easy and requires no tools.
Step 3: Choose the correct suction cups The suction cup is a vital component of any vacuum-based materials handling system. The quality and material characteristics of the suction cup are crucial. Productivity can be increased if the correct cup is used for a specific job. The belief that one cup will suit all applications is a common misconception. On the contrary, cups need to be tailored to suit specific purposes.
For instance, a box made of corrugated cardboard will require a different suction cup from a flat, but perhaps slightly oily, The cup’s durability, wear and oil resistance are important factors to bear in mind. As the friction between the suction cup and the surface is of vital importance, suction cups with high capability to handle shear forces resulting from rapid acceleration and retardation should be used. The design of the suction cup/fitting and the hardness of the lip are crucial. Suction cups in polyurethane with a soft, high friction, flexible lip and a stable body are a good choice for increased productivity in many applications. The soft durable lip gives excellent sealing capacity and the stable body a firm grip. Polyurethane has better abrasion and tear resistance than rubber. In addition, it has higher load bearing capacity and exceptional elastic memory. metal sheet.
Step 4: Optimize the release function and vacuum level In order to operate at optimal speed the vacuum system needs to have a suitable and efficient release mechanism, so that boxes, parts or components are released quickly. A passive release mechanism simply acts as a door that is opened and closed. For very quick release, such “doors” need to be placed as close to the suction cup as possible. Some applications may require an active release mechanism that allows compressed air to blow through the suction cup. As the active system will use more energy, it is important to optimize this type of release mechanism. Less than one second rather than one or two seconds of compressed air may be sufficient. In most vacuum systems it is also worth using a vacuum controlled pressure regulator to automatically hit optimal vacuum level. Depending on the application, 70 percent vacuum may be too high and should perhaps be reduced to 40 percent to avoid double picks and to improve productivity.
Step 5: Let the right people do the work An efficient vacuum system is made up by more than good components. Even if you have acquired the best components on the market, these need to be put to work in an optimized system by competent engineers. And what’s more, once the system is up and running, it needs to be operated by personnel that understand and know how to use it.