Manufacturers often assume that only large operations with deep pockets can benefit from robotics. In reality, small-and medium-sized businesses can benefit significantly from adding a robot or two to their operation. With the aid of the Siemens SIMATIC S7-1200F fail-safe programmable logic controller (PLC), organizations can integrate robots into their line to enhance product quality and manufacturing efficiency while maintaining operator safety. Here, we discuss how a factory integrator used the PLC to help one of its clients in the metal construction industry add a robotic cell for product handling. The system repositions the product in a way that reduces shipping costs. The system is fast, simple, safe, and effective.
Tailored to customer requirements
The manufacturer fabricates welded wire frame racks. Because of the shape, the racks have very low packing density unless they are properly oriented. To address this concern, the integrator developed a special lifting fixture and gripper solution designed to capture and manipulate the racks.
During fabrication, a rack pullout pushes the finished wire frame rack from the welding machine directly under the special gripper of the industrial robot (see figure 1). This gripper holds and lifts the wire frame, then flips it over. Next, the gripper transfers the rack to a second gripper attached to a lifting fixture, and then returns to the removal position. Meanwhile, the lifting fixture lowers and positions the gripper with the wire frame to a calculated location above the stack.
The next wire frame is placed on the stack by the industrial robot itself, without being turned over beforehand. This creates a stack of racks in alternating orientations, with the longitudinal wires of the rack always on one level, reducing the stacking height. As a result, more wire frames will fit on the truck, reducing transport costs for the customer.
Previously for this type of project, the integrator would have used an older, standard (non-failsafe) PLC, combined with safety relays or a dedicated safety controller. This architecture would certainly get the job done, but safety relays consume space, and add complexity and points of failure. Today, the integrator uses the SIMATIC S7-1200F for smaller projects and the SIMATIC S7-1500F for larger projects. Each of the two PLCs integrate safety functionality, making them capable of executing both safety and non-safety tasks.
The integrated safety approach provides a number of benefits. Eliminating the safety relays reduces size, wiring, and points of failure. Machine integration and commissioning become faster. The PLCs also provide a scalable solution. If the SIMATIC S7-1200F is not sufficient, the integrator can go to the SIMATIC S7-1500F without leaving the TIA Portal. Software modules OEMs develop for one controller can be used on the other. OEMs can also create software libraries for reuse. Less time spent on software development means faster completion of the project.
One of the big advantages of these PLCs is that the controllers feature built-in industrial Ethernet via PROFINET and PROFIsafe. All communication between the robot and the welding machine go through the SIMATIC S7-1200F and the integrated industrial Ethernet layer.
For the rack-stacking application, sensing gripper position is particularly important. The SIMATIC S7-1200F enabled the integrator to control and monitor all components in the robot cell such as the end position sensors for tracking the gripper position independent of the robot program. The system uses SIMATIC ET 200SP input and output modules on each gripper. The modules collect the signals from the end-position sensors. At that point, they transmit the data through the PROFINET cable.
In addition to standard communication over PROFINET, the integrator uses PROFIsafe for safety-related communication. Safety communications no longer requires a complex wiring scheme, which speeds commissioning.
The robot is linked to the welding machine in terms of safety, with an emergency stop system and shared protection areas. The robot can invoke the Safe Operation function, which means that its actions can be limited to certain areas. The operator can also use the controller to block or enable specific traverse paths depending on signaled states of the welding machine. This makes defining safety areas for robots and operators very flexible.
All information on the safety functions, including emergency stop and safety doors as well as end position sensors, is directly available in the controller and visualized on a SIMATIC KTP700 Basic Panel. Built-in diagnostics equip the unit to capture and present data without any additional programming. The design enables the end user to quickly diagnose faults all the way down to the channel fault. The operator also selects the recipes on the panel, depending on the type of wire frame or stack. Recipes are then communicated to the robot via the controller just like the signals from the welding machine or gripper sensors.
Manufacturers don’t need to be enormous in order to take advantage of the improved product quality and productivity delivered by robots. With integrated safety functionality, the SIMATIC S7-1200F controller is designed to make integration between robot and the rest of the manufacturing line faster, easier, and more reliable. It offers built-in diagnostics and a framework for software reuse designed to speed development software development and reduce cost. Projects become easier for system integrators and less expensive for the end-user, making robotics available for even small and mid-sized organizations.Have an Inquiry for Siemens about this article? Click Here >>