Pick & Place is the term used for this classic application for small parts grippers. Picking up items and putting them elsewhere in the proper place is a standard task that occurs in many handling and assembly processes – but not only there. For instance, in modern, large-scale laboratories which analyse thousands of blood, DNS or active agent samples; these are dispensed on intricate pipetting plates at high speeds. These plates are grasped by small robots and conveyed to the respective next step of the analytical procedure. Another typical application area is the assembly of circuit boards for power electronics, used in electrical machinery or switching systems, for example. The SCHUNK grippers pick up the components and place their contacts in the intended sockets on the circuit board. They must firmly grasp an item but may not, of course, damage the workpiece. In addition to a precise, finely-tuned force, in most processes it is especially the speed that plays a role: rapid gripping increases the productivity.
In the case of industrial grippers, pneumatically actuated systems have dominated up to now. This is attributable to both tradition and practical aspects. Pneumatic actuators have a high power density, which means that they can deliver relatively high force with a compact mass. This force is available virtually without time delay. As soon as the control valve is opened, the supplied compressed air can immediately accomplish the desired lifting work – in this case the grasping.
Pneumatics require their own infrastructure
Fundamentally, pneumatic actuators only have two states though: open or closed, full-power or no force at all. An incremental control is only possible with substantial control-technology-related effort and expense. Along with the electrical contacts for the control unit, a pneumatic gripper additionally requires connections for the compressed air lines. Under cramped conditions, which are not uncommon in the processing of small parts, this can certainly present a problem.
The greatest disadvantage, though, is the compressed air system itself. It requires at least one compressor and an air purifier, its own supply network, and a complicated control system in order that consistent pressure is available continuously and at all points. Therefore, particularly in new facilities, the proprietors are increasingly more inclined to do without this additional infrastructure and rely entirely on electrically operated actuator systems.
Proactive motor power
Thanks to the new electrical small parts gripper EGP 40, this can now be done on a purely electrical basis and, in fact completely without any trade-offs in terms of performance. With 140 Newtons, it develops an even greater closing force than its pneumatic counterpart the MPG-plus 40 – also manufactured by SCHUNK. This powerful performance is delivered by a 4-pin Brushless DC-Servomotor of the BX4-series from FAULHABER. The motor has an optimised, exceptionally high-power density. In other words, it provides a maximum of torque and power with respect to its mass. The compact, rugged design can be economically and automatically manufactured.
Because the motor runs cogging-free, its torque output does not depend on the position. By the same token, thanks to its minimal rotating mass, it attains a very high dynamic response. Already when setting into motion or in the lower rpm range, the full torque is immediately available. That is particularly important for this application, because the gripper fingers often only move a very short distance. A desirable side effect of the top-quality motor technology is its low energy consumption.
With these features the FAULHABER motor has become an important technical platform for the development of these electrical small parts grippers. "The gripper is conceived for easy, uncomplicated handling and integration in customer applications. Previously, motors with such performance as this were simply too expensive for installation in this type of device", relates development engineer Matthias Quaas from SCHUNK. "This motor type is based on an inexpensive concept, which made it possible for us to consider using a bought-in electrical drive in the first place. Moreover, it was very important to us to be able to rely on a sturdy and well-proven technology. And, this motor had already proven its reliability and long service life in many applications."
Due to space reasons, however, the control electronics had to be adapted to the requirements of SCHUNK. In order to fit in the gripper, the shape of the circuit board and the arrangement of components had to be optimised. They received a customer-specific connection and an EMC protection circuit to protect against electromagnetic interference. Furthermore, the software was adapted to the function of the gripper. "From my point of view, FAULHABER is not a supplier but a development partner", Matthias Quaas emphasises.
"The cooperative efforts were exceedingly constructive and always solution-oriented – we got outstanding support here."
Today, with the EGP 40, SCHUNK can offer the most powerful mechatronic small parts grippers with integrated electronics available in the global market. Its housing design and electrical power connections correspond to those of the equivalent pneumatic product MPG-plus 40. The sensor system and control signals are also identical. This way users can switch from pneumatic to electrical operation with a minimum of expense and effort. Further strengths of the gripper include an excellent relationship between clamping time and lift, the extremely precise operation of the gripper fingers – attributable to a high-performance cross-roller guide – and the fourfold adjustable gripping force. That which is only possible for pneumatics with an elaborate control system is incomparably easy here: through an opening on the side of the housing, switch positions are selectable for determining how firmly the gripper should grasp.
With this, the gripping force can also be adapted to formable or delicate workpieces. Besides, in many manufacturing processes the speed of the gripper is also crucial. In this case there is also an EGP 40 in a speed version. Within it, the motor works with different gear reduction. Although it is not quite as strong, it achieves incredibly short cycle times and is even quicker than the pneumatic versions.