High performance grippers from Festo
17 January 2012
Festo has introduced a range of pneumatically-operated grippers that are set to become high performance replacements for the company’s current generation HGx series of standard grippers. The new DHxS range includes parallel, three-point, radial and angular models, each offering a wide choice of sizes and stroke lengths. All the new grippers are characterised by compact dimensions, optimised gripping retention force and high reliability.
The four different styles of gripper in the new 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 pneumatic pressure loss. 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.
Festo has 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 older series and by most competitive products on the market. This new design produces considerably more gripping force – on average, as much as 40% higher – 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 upon the load it has to move.
For maximum applications flexibility, the DHPS parallel grippers are available in six sizes, spanning piston diameters 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 much-reduced risk of jaw breakage under extreme load. For example, the parallel grippers can on average accommodate 130% more torque than previous-generation models, and for the three-point grippers this figure rises to 280% more than previous models.
Festo has modified the lever mechanism that transfers the force generated by the linear motion of the piston rod to the low-backlash gripper jaws radically, resulting in much higher levels of repeatability. Typically, the repeatability of the new grippers’ jaw positioning accuracy is 100 percent better, at only 20 microns, compared to the 40 micron figure previously. Furthermore, because the levers are directly in mesh with the gripper jaws, there is no need for additional synchronisation.
The significant improvements to gripper performance and accuracy are reinforced by enhancements to the standard of mounting interface. All four types of gripper are fitted with mounting hole centering sleeves to facilitate fast and accurate location, and the parallel and three-finger models are also equipped with centering sleeves in the gripper jaws.
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, which can detect a flag on the fingers of radial and angular grippers, to provide confirmation of jaw movements.
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 to 10 V analogue output which is directly proportional to piston movement over a 0 to 40 mm range, and provides exceptionally precise feedback, with a repetition accuracy of plus or minus 25 microns.
Weighing just 10g, the transmitter is ideal 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 need for signal conditioning circuits, and can be used to determine the size of object being gripped or the quality of grip, as well as indicating gripper movement.
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