New sensors help control robots for improved productivity
April 19, 2013 by Schunk
Complex tasks such as assembling, deburring and polishing can now be undertaken by robots, which traditionally were manually done in the past.
Sensors are playing key roles in many manual jobs that are now being undertaken by robots. Force-moment sensors, for example, are able to precisely identify process parameters and transmit them to the control unit. If the robot path is readjusted in real time on the basis of this data, constant forces and exactly reproducible results can be achieved. Modern, standardized sensor solutions are compact, can completely merge with the actuator and are easy to operate.
Sensors have a hidden potential
The currently most versatile force-moment sensor for industrial automation measures forces and moments in all six degrees of freedom. The sixth axis is equipped with an interface for robot control, whereby connection is considerably simplified. The high-precision sensor disposes of a high-speed data output with up to 7000 Hz, five possible communication protocols (Ethernet, Ethernet/IP, DeviceNet, Profinet, and a CAN-Bus interface), remote control via LAN, a configuration via web interface, and a unique interface compatibility is offered for many applications. It can be used for product tests, robot assemblies,
machining tasks such as grinding and polishing, robot surgery, and for applications in the fields of rehabilitation, neurology, and others. Since the sensor also allows highly dynamic control concepts, it can also be used for automating difficult assembly, machining, and finishing tasks, which have in the past, either done by hand, or with complex special machines.
Tactile sensors belong in the top class of modern sensors. They allow site-resolved monitoring of the gripping force and surface. This way, it is possible to identify objects and to grip sensitively at the same time. With tactile sensors, fragile parts with different geometries can be reliably and safely handled. Moreover, it is possible to position and join changing objects. In the future, tactile sensors will particularly play an increasing role in the field of service robotics. They transform gripper hands into sensitive helpers, and can also be effectively used in complex and disordered surroundings.
Accessories for grinding, polishing and deburring
Robot accessories are particularly available for undefined processing methods such as grinding, polishing, brushing and deburring, are process-reliable, and the use of sensors is not necessary. They compensate tool wear and inaccuracies in workpiece positioning, as well as deviations of the robot arm from its given path. Thus the quality of the machining result is improved, and programming time can be reduced by up to 75 per cent. Deburring spindles imitate the manual deburring process as accurately as possible. They are working at speeds of up to 65.000 rpm. Their spindle and motor system is flexibly seated on a self-aligning bearing. Several small pneumatic pistons ensure that the spindles can compensate up to nine millimeters in radial or axial direction, and therefore the compressed air motor can move relative to the housing, and compensates deviations between the tool path and the actual workpiece contour. A uniform result is always achieved, even if parts are irregularly shaped. The rigidity of the deburring spindle can be controlled via a separate air connection, and clean chamfering edges are ensured at every installation position.
Compensation units ensure that the required flexibility between effector and robot arm during joining, assembling, or insertion by the robot is ensured. They help to avoid system disturbances and damages, and are increasing process reliability. Flexibility in two directions is defined via springs with adjusting screws; in three directions via elastomer elements. Since the units do without pneumatic elements, they are very flat and excellently suitable for applications in confined spaces. Smoothly running roller guides even compensate low compensation forces without stick-slip effects. Spring-actuated resetting pistons ensure a high repeat accuracy.
Automated tool change
Even for changing grippers, tools and other effectors, the fitting robot accessory can reduce manual works or even replace them. While a trained operator needs between ten and thirty minutes for manually retrofitting a pneumatic effector, a quick-change system settles the same operation in ten to thirty seconds, whereby the mere locking and unlocking operation is done in milliseconds. The use of the speedy changing systems makes sense if systems are regularly adapted to new products and product variants, where various effectors are necessary for handling or machining, or where downtimes due to maintenance work of components and tools need to be minimized. As a general rule, they consist of two components: A quick-change head which is mounted at the robot arm, and a quick-change adapter which is connected with the tool. During tool change both parts are automatically or manually coupled and at the same time all the electric, pneumatic, and hydraulic feed-throughs are connected with each other. This ideally happens pneumatically via a patented self-retaining locking system, and is controlled via integrated sensors. Since the orientation of the effector is already defined by the quick-change system, no time is lost for its readjustment.
When choosing a quick-change system, users and system integrators should take care of a possibly low weight-force ratio, short changing times, and exactly dimensioned energy transmission modules. Modular systems are particularly economic, if various electronics and fluid modules can be combined with each other depending on the application. If locking and unlocking is carried out without force, it would be ideal if a so-called no-touch locking system is used, which also ensures safe locking if there is a clearance of a few millimeters between head and adapter. Heavy-duty changing systems are suitable for handling of heavy workpieces, and work with heavy grippers, vacuum spiders, hydraulically, pneumatically or electrically driven machining spindles, applications with rivets, welding tongues, or bolt welding with automatic material feeding. Moreover, they can be used in the automotive industry, where assembly or press bonding is common. Due to their high performance, they can be also used for setup of flexible production lines, where light and heavy workpiece are alternately machined.
Quick-change systems are particularly valuable if they are equipped with a uniform mounting flange on all four outer surfaces. They offer more space for modules and feed-throughs, and they supply coupled effectors pneumatically, hydraulically or electrically. There is one exception, the signal module, which is coupled and decoupled via the quick-change system, but the remaining three sides can be randomly equipped.
The Schunk program on robot accessories also offers high power modules, self-sealing fluid modules, bus transmission modules, and servo modules. On request, they can be customer-specifically adapted. The variety of electronic modules offered by the family-owned company for controlling the actuators and sensors is also second to none. It comprises modules for Profibus, CAN, RS232, and Ethernet TCP/IP, too. To learn more, visit the Schunk website at http://www.ca.schunk.com.