Servo pneumatic gripper offers more flexibility at lower cost

Dean Palmer takes a look at the latest intelligent, servo pneumatic gripper for industrial robots, that improves handling flexibility at a lower cost than its electric counterparts

An intelligent, servo pneumatic precision gripper has been developed for automated assembly and handling robots that offers excellent flexibility and performance at a much lower price, while its compact, integrated design ensures sustained environmental compatibility through reduced energy consumption. The HGPP-12 gripper from Festo consists of an extruded aluminium housing incorporating the cylinder bore to accommodate two pneumatic pistons. The force generated by the linear motion is translated into the gripper jaw movement via these pneumatic pistons, which act directly on the gripper jaws that are installed in the housing by using pressed-in straight pins. To synchronise the piston movement, a gearwheel is located in the centre of the housing, which is positioned horizontally to the cylinder bore and meshes with both pistons. And, to ensure a backlash-free guideway for the gripper jaws, guide elements are fitted in the housing and pre-tensioned using socket head screws. According to Festo, modifications were necessary in the initial development phase. These involved increasing the standard gripper jaw stroke from 2.5mm to 10mm per jaw and eliminating the mechanical forced coupling to enable free positioning of the individual gripper jaws. Grippers for industrial robots are normally used to connect the workpiece and handling object for the duration of the handling or assembly process. Because of the diversity of applications for grippers, there has been a multitude of products developed over the last ten years or so. Most designs available today are equipped with coupled, non-controllable gripper jaws which are only able to open or close. Other electrically-actuated grippers are relatively expensive, large and heavy and offer limited sustained holding forces subject to pronounced increases in temperature. The development of intelligent gripper technologies has helped to improve the flexibility of such systems, but market acceptance has been limited due to the high degree of complexity of such devices and the attendant costs. Hence, Festo's new HGPP-12 gripper which does appear to boast the best overall cost-performance-flexibility ratio on the market. Preliminary research on the HGPP-12 revealed that the most suitable proportional actuators for such a compact drive device were Festo's 0.6mm diameter, 3/2 piezo valves with rocker technology. Continuous displacement of the valve's bending element (step response time is around 1ms) can be achieved by using appropriate control technology, thereby achieving highly dynamic servo functionality. By coupling two modules deployed as 2/2 valves with valve connection '3' blocked (one module for ventilation, one for evacuation), a leakage-free 3/3 valve can be produced which is ideal for control tasks. Subordinate pressure control is affected by using three pressure sensors that detect pressure in each cylinder chamber. Position detection is carried out by means of a Hall Effect sensor from the standard gripper in order to enable integrated position detection by tapping the analogue, amplified sensor voltage. Following a calibration process, the signal quality and accuracy is more than adequate for positioning of the produced gripper. Steve Sands, UK MD at Festo, told Eureka: "The gripper guarantees autonomous, mobile deployment as a result of the complete integration of all electronic control and power supply elements."