Intelligent assist devices is a new category of materials handling equipment led by a select band of companies such as Ingersoll-Rand Zimmerman, Gorbel, Tawi, Liftronic and Dematic. Essentially they are taking air balancers, either the concept or the actual 40 year old technology, and moving it forward with electronics to meet the needs of today’s market place. The market, in this context, primarily means the motor manufacturers Ford and General Motors which have taken the lead in encouraging research and development in the field. The products that are now being produced, however, are suitable for any application where lifting duties are repetitive, and not just for production line car assembly.
Air balancers were patented in 1959 by Zimmerman, a company subsequently acquired by Ingersoll-Rand. They enable a person, no matter how weak, to lift and place a heavy load with minimum effort. The development of IADs in the past three or four years, under the patronage of the motor industry, has moved the technology forward, adding electronics to combine the benefits of robotics with the brain and intuition of a human. With the new products, there is no build up of momentum or inertia as the load is moved.
There appear to be two general categories of IADs – those that have retained air power, and those that have moved on to electric power. In the latter category are Gorbel’s G-Force, an electro-servo controller device launched earlier this year, and a similar product from Tawi of Sweden. Ingersoll-Rand Zimmerman, however, has just brought out the first air balancer that has electronic controls – the Intelift. Dematic is also understood to be developing its own electro-pneumatic balancer design.
Fully electric IADs have the benefit of being very precise and are good for high-speed working. There is always a delay with air powered devices while the can, or cylinder, fills up with air and empties. Electric powered devices do not have this problem. They are more precise and respond significantly faster than air balancers to inputs.
But although lifters like the G-Force are quick and therefore hard to beat for repetitive movements, they are not wholly rated duty cycle because eventually the motor will burn out if pushed beyond the limit. Air power can be used unceasingly.
The use of electric over air, or rather the introduction of electronic intelligence, brings a new dimension to the basic air balancer. On the downside, being air powered, they still have the delay while the can fills and empties and so are not as quick as electric powered devices such as the G-Force. But the key advantage of the Intelift, when compared to fully electric competitors, is its lifting capacity. The smallest Intelift unit in the range has a maximum capacity of 150lb (68kg), while the biggest lifts up to 1,000lb (454kg). For fully electric balancers, the maximum capacity yet achieved is 150lb.
The Intelift originated from Ingersoll-Rand’s research and development department. The challenge was to provide a solution to situations where operators had to pick up several different weights with the same device, be able to control the position of the device when the part is in mid air, not drop parts accidentally, add weight to a part already lifted, and include intent sensors.
The Intelift incorporates a closed loop feedback system to enhance the motion capabilities of the balancer and provide certain innovative features.
The main application where the Intelift balancer comes into its own is when pouring. With other devices, as the container empties and the load on the end of the hook lightens, the container itself rises up. The Intelift is ‘self-balancing’ and, by continually reading the weight of the load and compensating, it holds the container in place as it empties its load. No adjustments are needed for different weights.
By setting the control panel, the micro-controller can operate in either position control or float mode. In position control configuration the feedback signal from the encoder is used to hold the load as steady as possible. This is achieved by reading the number of counts on the encoder wheel that occur as the load drifts away from its original position while dumping the load. In the float mode, the micro-controller maintains constant pressure in the balancer with a pressure sensor. This allows the operator to manually adjust the load vertically to a new position, for fine adjustments. The load then continues to float at the new position.
The Intelift also has what the marketers call a ‘smart drop’ feature. When the ‘clamp/unclamp’ button is held depressed, the load is lowered until only the weight of the end-effector is being supported. The clamp is then allowed to open and release the load. The controller monitors the pressure in the balancer and calculates a time-based control signal. This functions as a force control signal from the end-effector weight.
An ‘interlock’ feature prevents the device from releasing the load if the unclamp button is pressed before the load is fully supported. The Intelift can also be used with complex end effectors.
An optional feature called ‘part present’ enables clamping of loads in poor visibility. When used with vacuum cup devices, it reduces air consumption and the noise level.
An up control disable feature ensures loads are securely clamped before allowing them to be lifted.
The Intelift also has a three speed select feature, achieved by the use of valves. Ingersoll-Rand’s senior project engineer Warren Seith explains: “On the Intelift, the three speeds that can be selected by the operator are possible since the microprocessor calculates velocity using the encoder signal. It targets the selected speed and opens or closes valves as required to accelerate to, and maintain the selected speed. This algorithm provides accurate speed control regardless of weight.” Although this helps reduce the disadvantage of the momentary delays while air comes in and out, this can never be eliminated with air hoists.
Ingersoll-Rand marketing manager Umesh Cooduvalli acknowledges that there is always the constraint of the compressibility of air, but he says that the Intelift is as fast and precise as any pneumatic balancer can ever be. “We have reached the peak with air,” he says. “We cannot go any further.” But recognising that for many applications it is speed and precision that are the key issues, Ingersoll-Rand has now turned its attention to developing an electric balancer. The plan is to launch it in June 2001, but a prototype may be exhibited at the Promat show in Chicago next February. What will differentiate this product from the competition, says Cooduvalli, is that it will be able to handle loads up to 275lb.
