Precision Gripper System for Small Parts
Getting a Grip on Precision
A new small parts gripper from SCHUNK functions with micro brushless DC servo motors – and without compressed air.
A small gripping system that is both quick and powerful – up to now, that was often only possible with pneumatics. With compressed air, large amounts of pressure can be conveyed virtually without any time lag. However, a compressed air supply requires a complex infrastructure, and having to provide it for every production step can be difficult and expensive. Fortunately, this is no longer necessary – thanks to the mechatronics-based EGP 40 from SCHUNK. The new gripper from the leading expert for work-holding technology and gripper systems easily achieves the same performance of its pneumatic counterparts. The drive that makes this performance possible is a small brushless DC motor from FAULHABER and MICROMO.
This classic application for grippers of small parts is typically referred to as "Pick & Place". Picking up items and putting them elsewhere in a desired position or place is a standard task that occurs in many handling and assembly processes, but this task is also found in a myriad of other applications and industries. For instance, modern large-scale laboratories responsible for analyzing thousands of blood, DNS or active agent samples also benefit from pick and place automation. The lab specimen samples are dispensed on intricate pipetting plates at high speeds. The pipetting 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. The SCHUNK grippers pick up the components and precisely place the contacts in the intended sockets on the circuit board. The grippers must firmly grasp an item but must not damage the workpiece. In addition to using precise and finely-tuned force, most processes also require challenging and fast speeds: rapid gripping generally leads to higher productivity.
In the case of industrial grippers, pneumatically actuated systems have dominated until 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, and with almost no 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.
Despite the previously mentioned strengths and performance of pneumatically actuated systems, an obvious weakness should also be recognized and considered: pneumatic systems require a supportive infrastructure. Fundamentally, pneumatic actuators only have two states: open or closed, delivering full power or zero force. 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, not uncommon in the processing of small parts, this can certainly present additional challenges. 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 to ensure consistent pressure is available continuously and at all points. With all of these added obstacles, it makes sense 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, without compromising on 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 the 2232 BX4, a 4-pole brushless DC servo motor of the FAULAHBER BX4 series. The motor has an optimized, exceptionally high power density, providing 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. When setting into motion or in the lower rpm range, the full torque is immediately available. This capability is particularly important for this application, because the gripper fingers often only need to move a very minimal distance. A desirable side effect of the top quality motor technology is its low energy consumption.
With these features the FAULHABER brushless DC servo 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, brushless DC motors with such impressive performance 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 other applications."
Developing Customized Solutions and Service
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 optimized. 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 and MICROMO are not just suppliers, but development partners", Matthias Quaas emphasizes.
"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 allows the users to 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 high 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.
For more applications similar to this one, visit the Robotics and Industrial Automation applications page. To learn more about innovative designs and motion solutions from MICROMO and FAULHABER, contact a member of our team, today.