working in a vacuum9 October 2018
Vacuum lifting can provide a solution for certain loads. Julian Champkin reports.
Hooks are useful for lifting loads. For certain applications, vacuum lifters can be better. Their image is of a system that is primarily associated with glazing. Glazing robots, essentially mini-cranes with an articulated arm carrying one or several vacuum pads and manipulated by an operator standing behind or beside it, are becoming ubiquitous. The smooth surface of glass is ideal for sealing the vacuum within the rubber suction pad, and for preserving it once the vacuum pump has been turned off. Glass loads are light enough for the vacuum to support; and the fragile nature of glass makes other solutions, such as slings below hooks, liable to damage or break the load. Hence the widespread use of vacuum lifting for glass.
The glass vacuum lifter is becoming ever more sophisticated. The Hydraulica 2000 from GGR, for example, can lift the pane, rotate it in two axial directions, position it, and, when the glass has been secured, release it; and all this if necessary by remote wireless control.
Glass, however, is not the only thing that can be lifted. Anything that is not too porous, and whose surface is not too rough, can be a candidate, especially in a manufacturing or fabricating environment. Plywood panels are a typical example, but again they are light, and vacuum loads are far from limited to the lightweight. The Vacuum Lifting Company’s TT16000 can lift loads as heavy as 16t, and this despite being battery powered. The Rutherford Appleton laboratory near Didcot, Oxfordshire uses one, with a radiocontrolled valve, to lift 200mm-thick steel slabs to construct nuclear accelerator shielding. In Varna, Bulgaria, twin 10t batterypowered Vacuum Lifting Company units lift 20t steel plates. At the other end of the size scale, small portable units are used on paving slabs and kerb stones. One great advantage of vacuum lifting is that the load need offer no edges to form a grip.
Thus polished stone paving slabs can be grasped, and lifted from the floor, by either a hand-held vacuum lifter, or by portable units such as the Vacuum Lifting Company’s Archback Mini below the hook of a small hoist.
Vacuum lifter technology includes easy and quick pad changeover systems to different pad sizes and layouts to suit the product. An audio-visual alarm can warn of any vacuum failure.
Curved surfaces, such as pipes, are not difficult to manage: multiple suction pads on an adjustable frame are used and it is simply a matter of arranging the frame to give the pads a snug fit. Nor need the loads they be absolutely smooth and non-porous. It obviously helps if they are; but cardboard and even plastic and paper sacks can be lifted by suction.
The explosive growth of internet shopping has created large warehouses with a need for automated picking and handling of packages of any different sizes and weights. It is a demand that the Piab company Vaculex are meeting with their TP handling system, which eliminates the need for heavy lifting. A vacuum cup on the end of a lifter, with a hand controller just above the cup, can grip cardboard boxes or parcels up to 65kg and be guided by the operator for loading, stacking on pallets, or onto or off a production line.
Those are low-value, high-volume applications where speed, and often automated sorting are paramount. Another area of vacuum lifting is for high-value, highspecification components where provision for lifting hooks would be a serous impediment. For more than 30 years the French company Acimex has been designing vacuum lifters for handling aircraft components. Bombardier, British Airways, and Dassault have been among their customers. These automatic handling devices can fasten onto wings or fuselage sections without damaging or deforming them; 5t capacities are common.
Such loads of course are of extreme value. A fall would be catastophic. Two separate vacuum circuits therefore provide optimum safety. The Vacuum Lifting Company is also in this field, with a 30m 22-pad wingskin lifter used on the Airbus. Each pad has individual status monitoring and feedback for maximum safety. The same company’s HTS5LB similarly is a dual circuit ultra high specification battery powered lifter for items of extremely high value. It has 90-degree tilting capability and has been used to lift curved nuclear submarine farings.
Nor is porosity a bar. The FLEXR lifter from Woods Powrgrip is marketed as capable of lifting porous material such as concrete and particleboard in production or fabrication environments.
Slippage is a factor to consider. A vacuum does not have to be inadequate for a load to escape: friction is all that prevents a load from sliding sideways off the vacuum cups.
Suction cups can be made of alternativeformulation rubber compounds to address these and other issues. Different compounds excel in different areas, of slippage resistance, resistance to marking the load, abrasion and other factors. Thus Woods Powrgrip offers, among other options, cups made of an oilresistant rubber (oil can attack normal rubbers); a low-marking rubber, for light-coloured material; of UV-resistant rubber for outdoor use; and heat-resistant rubbers for removing glass from temping ovens—Powrgrip warn that these, being less flexible, have less lift than standard rubber. They have a rubber that can handle painted and silk-screened glass without leaving marks; and more flexible cups for gripping textured surfaces. Cups of different materials, or sizes, can be exchanged on the mounting framework as suits the load.
Vacuum supply can be by battery, or AC power, or, in a production facility, via centralised vacuum lines. “Vacuum lifters are getting intelligent,” says Barry Wood, Woods Powrgrip sales director. “So operators need not be expert in detail. Diagnostic screens now tell you what you need to know, when you need to know it. They give information such as when the battery charge is bad, or when the battery itself is bad; it is a heads-up on maintenance and safety. Digital readouts can give more sophisticated information on the battery, on when the pump is running or not running and so on. There have been small increments in the technology over the years, but smart technology has been the big jump.”
Flexible, non-rigid loads might seem insurmountable for vacuum lifting. Not so. Paper and plastic sacks, as used, for example, in the chemicals industry, are now well within the capabilities. “When handling chemicals, operators must be particularly careful that no tears or holes form in the sacks, allowing substances to leak out,” says Schmalz, who have been making vacuum lifters for three decades. Schmalz divide their offerings into two categories: ‘Vacumaster’ which is a vacuum gripping device mounted on a conventional chain hoist, and their ‘Jumbo’ tube lifter system— essentially a gripping head and a lifter as an integrated unit in which the vacuum itself lifts as well as grasps the load. Vaculex, mentioned above, uses a similar technology. In the case of the Jumbo, it consists of a vacuum generator, a lifting tube, an operating valve and a vacuum gripper. The gripper hangs from the end of a flexible airtight tube, which itself hangs from an overhead mount and is connected to the vacuum generator. In operation, the vacuum generator continually evacuates air from the system. The pressure difference draws the workpiece up against the vacuum gripper thus holding it and forming a seal. Once the workpiece has sealed off the end of the lifting tube the continued evacuation of air causes the lift tube to contract. This is what raises the workpiece. The operator can bleed air into the system though a trigger mechanism just above the gripper; this causes the lift tube to expand, lowering the load. In this way lift height, says Schmalz, can be precisely controlled. When the trigger valve is opened completely, air pressure inside the lift tube becomes atmospheric and the load is released.
The tube lifter, says Schmalz, enables operators to lift loads ergonomically and safely, and with high cycle rates. The JumboFlex allows lighter goods up to 50kg to be moved. The larger JumboSprint can handle up to 300kg with a maximum lift of 2,100mm. The one-finger control makes lifting, lowering and releasing the load extremely intuitive, they say, fits comfortably in the hand, and allows the operator to work for a long period of time without fatigue. It comes with a quick-change system for replacing the vacuum gripper to suit the load. And workpieces need not be gripped from the top; if the vacuum gripper is applied to the side of the piece it automatically swings on its tube when it is lifted so that the gripped side is uppermost.
A radio remote control to the vacuum generator can switch it off easily when not in use, which Schmalz says can offer 40% in potential energy savings. The suction cups are resistant to salts, vapours and chemicals; and the JumboSprintEx is ATEX certified for operation in explosion protection zones. Conductive parts are connected for potential equalization to eliminate sparks; the lift tube is made form a conductive material for the same reason; and the vacuum generator can be driven by compressed air. Lifting of bags, barrels and cardboard boxes in explosive environments therefore becomes possible.