Posted to News on 11th Feb 2012, 08:51
Compact pneumatic grippers 'set new performance standard'
Festo is launching a new range of DHxS pneumatic grippers, which the company claims will set a new performance standard. These are described as high-performance replacements for Festo's current generation HGx series of standard grippers. The DHxS range includes parallel, three-point, radial and angular models, each offering a wide choice of sizes and stroke lengths to ensure that the right function and capacity are available to meet the demands of diverse applications. All the new grippers are characterised by compact dimensions, optimised gripping retention force and high reliability. They are suitable for handling and assembly systems that demand cost-effective, lightweight end-effectors.
Pneumatic-mechanical grippers have a simple task to perform: reliable operation with fast cycle times. However, to create products that achieve this, manufacturers have to balance conflicting criteria such as the needs for low weight, high gripping forces, minimal dimensions and improved performance, while at the same time striving to lower production costs. Festo says it has successfully met all these challenges with the DHxS series of grippers.
The four different styles of gripper in the range share a number of novel design attributes, aimed specifically at maximising performance and minimising cost. All the grippers are available with double-acting piston drives, as well as an optional spring-assisted safety mechanism that ensures the gripper jaws will continue to hold their position in the event of a loss of air pressure. This option obviates the need for complex and costly additional safety circuits. The grippers are also effectively overload-proof; an integrated fixed flow restrictor acts as a safety buffer, protecting the unit against overloading during high-speed motion of the gripper jaws and preventing damage due to excessively high speeds.
Greater grip
Festo's designers have increased the gripping force of the parallel grippers while retaining the same external dimensions of the older series by utilising an oval piston instead of the twin smaller pistons employed by the previous series and by most competitive products on the market. This new design produces considerably more gripping force - on average, as much as 40 per cent higher - thereby enabling machine builders to use a smaller, lighter gripper for the same task, with a commensurate reduction in the size and weight of the axis carrying the gripper. This has a significant cost benefit for multi-axis handling systems, where the size of each axis depends on the load it has to move.
For maximum applications flexibility, the DHPS parallel grippers are available in six sizes, spanning bore sizes from 6 to 35mm with individual jaw strokes from 2 to 12.5mm. The largest model can produce a total gripping force of up to 970N.
The new parallel and three-point grippers employ an innovative T-slot guidance system and cam mechanism that enables the jaws to accommodate much higher torque moments, leading to improved reliability and a reduced risk of jaw breakage under extreme load. For example, the parallel grippers can, on average, accommodate 130 per cent more torque than previous-generation models - and for the three-point grippers, this figure rises to 280 per cent.
Improved repeatability
Festo has radically modified the lever mechanism that transfers the force generated by the linear motion of the piston rod to the low-backlash gripper jaws, resulting in improved repeatability. Typically the repeatability of the new grippers' jaw positioning accuracy is only 20 microns, compared to 40 microns previously. Furthermore, because the levers are directly in mesh with the gripper jaws, there is no need for additional synchronisation.
The significant improvements in gripper performance and accuracy are reinforced by enhancements to the standard of mounting interface. All four types of gripper are fitted with mounting hole centring sleeves to facilitate fast and accurate location, and the parallel and three-finger models are also equipped with centring sleeves in the gripper jaws.
Position sensing
All the new DHxs grippers are equipped with an integral magnet on their pistons, and their bodies have T-slots for easy mounting of sensors. Festo offers two types of proximity sensors: one detects the presence of the internal magnet; the other mounts inside the same slot but features an 'outward-looking' sensor to detect a flag on the fingers of radial and angular grippers.
For more demanding applications, Festo offers the SMAT-8M position transmitter. This also mounts in the gripper's sensor slot and detects the internal magnet. However, it produces a 0-10V analogue output that is directly proportional to piston movement over a 0-40mm range and provides exceptionally precise feedback, with a repetition accuracy of +/-25 microns. Weighing just 10g, the transmitter is suitable for applications where the total weight of the gripper module needs to be kept as low as possible. The analogue output can be fed direct to a PLC without the need for signal conditioning circuits, and can be used to determine the size of object an being gripped or the quality of grip, as well as indicating gripper movement.
Festo's new DHxS grippers are suitable for mid-performance handling tasks. The company produces an extensive range of gripper products, including models optimised for light weight, harsh environments and heavy-duty applications. Choosing the optimum gripper for a particular application is a demanding task, so Festo has developed a powerful gripper selector tool to aid users in the decision-making process. The free online software takes into account the size, weight and forces acting on the gripper, as well as the environmental conditions, and incorporates Festo's extensive gripper technology knowledge-base to help users achieve 'right first time' results easily and quickly.
Follow the link for more information about Festo grippers.
