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Floating a vision of levitating production systems

30 April, 2019

In tomorrow’s factories, workpieces will be transported flexibly between workstations on magnetically levitated carriers. This vision of the future was demonstrated at a recent German exhibition by two rival automation companies who believe that their technologies will help manufacturers to achieve “batch size one”. Contributing editor Tony Sacks reports.

The past few years have seen the arrival of several linear motion systems designed to transport items along production lines. The ability to move items individually along lines to stations where processes are performed upon them is seen as a key technology to achieving the Industry 4.0 goal of producing items in “batch size one”. The idea is that every item rolling off a production line could be different, and tailored to the precise requirements of a specific customer.

The various linear transport systems are designed to allow bespoke production to be achieved at high speeds. Instead of hundreds or thousands of identical products moving along inflexible conveyor lines and having identical processes performed on them, the new breed of linear systems allow items to be carried on platforms (known as carriers, movers or shuttles) that can follow individual paths taking the item to those processes specified by the end-customer. In some cases, they can bypass processes that are not required for that item.

Smart Machines & Factories looked at some of the contenders last June. They each adopt slightly different approaches to their design and capabilities and some are tailored to specific types of application.

What most of these systems have in common is that their carriages run along tracks on rollers, usually propelled by some form of linear motor. But at the recent SPS IPC Drives automation exhibition in Germany, two new ideas emerged – both of which rely on carriers that “float” electromagnetically rather than running along fixed tracks. The two systems were being demonstrated on neighbouring stands by Beckhoff and Bosch Rexroth.

Superficially, at least, the systems have much in common. They are designed to offer a lot more flexibility in movement than fixed-rail systems. So, for example, they can be programmed to move anywhere in a two-dimensional (X-Y) planar area. Some movement is also possible in the vertical (Z) direction, with the carriers being able to move a few millimetres up and down. They can also rotate, which could be a useful capability for presenting items to production processes at precise angles. And, finally, they can even be tilted slightly – a facility that could be used, for example, to prevent liquids from spilling when they are being transported at high speeds in open containers.

The two systems operate on slightly different principles, although their developers are not revealing the full details at this stage. In both cases, the carriers float above an array of “tiles” containing some of the technology that enables them to levitate.

Announcing Beckhoff’s technology – called XPlanar – managing director Hans Beckhoff hailed it as a “motion revolution” and compared it to a “magic carpet”. The carriers, known as “movers”, float above square tiles measuring 240 x 240mm, and can travel at speeds of up to 4m/s. They can accelerate at rates of up to 2 g and are claimed to be able to position the items they are carrying with a repeatability of 50µm.

At the SPS show, Beckhoff demonstrated four sizes of mover, ranging from a 95 x 95mm version that can carry loads of up to 0.4kg, to a 275 x 275mm version that can handle up to 6kg. The movers can be linked together to transport heavier loads. They can even travel vertically up and down walls or be hung upside-down from ceilings. The movers are passive, containing no electronics or mechanics.

Beckhoff’s movers can “fly” at height of 1–5mm above the tiles, can tilt by up to five degrees, and can rotate by up to 15 degrees (or 360 degrees if they are above a special type of tile). They can move freely and individually, allowing production line flows to be divided or logjams to be avoided. The contact-free technology avoids wear and contamination by friction particles.

In a standby mode, each tile draws around 13W. During operation, the power requirement varies depending on factors such as the load on a mover, whether it is moving and its height above the tiles. For example, a mover “flying” 2mm above the tiles without a load would draw 115W.

The sealed, watertight and chemical-resistant movers contain permanent magnets and are propelled by 3D travelling magnetic fields that are generated in the tiles which house flat coils as well as the electronics needed to detect and control the movers. The tiles are linked to a PC-based controller running Beckhoff’s TwinCat software via a 1Gbit/s version of EtherCat that Beckhoff also launched at the show. The controller synchronises the motion of the movers and ensures that they do not collide. It also optimises their paths automatically and can control a group together to handle heavier loads.

Beckhoff believes that the scalable XPlanar technology (which is based on a system called Xbot, originally developed by a Canadian firm called Planar Motor) will open up new avenues in machine design, offering machine-builders unprecedented levels of flexibility and simplicity. For example, in some applications the technology will be able to replace robots or inflexible mechanical devices.

As well as being assembled in rectangular arrays, the XPlanar tiles can also be arranged as linear tracks. Extra tiles can be added to create waiting zones, or fast-track lanes than allow overtaking to avoid congestion. The movers can travel in any direction across a tile.

Beckhoff envisages the system being used in automated packaging, assembly, sorting and order-picking processes. There is a choice of surfaces – easy-to-clean glass, hygienic stainless-steel, or plastic film – making it attractive for use in cleanrooms, in the pharmaceutical and food industries, and in vacuum applications. Because the system is free from fiction, it should not generate particles or dust.

Rexroth’s rival system is at an earlier stage of development than Beckhoff’s. At SPS, the technology did not yet have a name. Rexroth claims to have developed the system entirely in-house at its corporate research centre, where it has been working on the project for two years. The patented technology can currently carry loads of up to 1.5kg, which the company plans to increase to 3kg, with a target of eventually raising the payload capacity to around 20kg. The movers can travel at speeds of up to 4m/s, and the positioning accuracy is claimed to be 100µm during transport, and 2µm when stopped for processing.

As well as magnets, Rexroth’s movers contain a battery-powered measurement system. They operate at a variable height of up to 20mm above the 240 x 240mm tiles, and can rotate “endlessly” through 360 degrees above any tile. Rexroth says that its system will not generate any heat, even when carrying maximum loads and operating with extended levitation times. Also, there are no significant electric or magnetic fields on the tops of the movers.

The Rexroth system is still at the laboratory stage, but the company is hoping to start pilot installations later this year, before bringing the system to the market in about two years’ time. It expects typical uses to include micro-assembly, semiconductor production, packaging and cleanroom applications.

Beckhoff believes that its levitating transport system with its “six degrees of freedom” will open up new avenues in machine design. It says that the movers will enable flexible, precise and highly dynamic positioning, and will simplify the design of machines and plants.

Initially, Beckhoff is offering a starter kit in two versions to provide an introduction to the technology. The kits will contain all of the necessary components, including pre-assembled planar tiles installed in a frame. The electrical components and an industrial PC are installed in a control cabinet. The kits contain differing numbers and sizes of tiles.

If Beckhoff and Rexroth are correct, then the factory of the future could look very different with scores of movers whizzing around silently and independently carrying their loads from one processing workstation to the next.

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