So you have invested in a robotic system or automated machine to boost the speed and efficiency of your processes. But do you know that the key to accurate and thus cost-effective automation is having the right positioner which matches the capabilities of the robot? Having an incompatible positioner can decrease yield and your production speed.
Requirements for robotic positioners
Positioners used by humans are not optimised for robotic use. While a human operator can tolerate more gear backlash, or subconsciously compensate for variation during work, these same considerations which give automated processes their speed also demand the work pieces to be precisely positioned, time after time.
Positioners and orienters provide this ordered and repeatable environment, with very fine tolerances for creep and backlash. Additionally positioners need to be able to stand up to the repeated forces caused by the speed of movement within the automated workstation.
Related to speed requirements are the load capacities of positioners – robust positioners are capable of manipulating larger workpieces quickly, while retaining pin-point accuracy.
Some positioners come with counter bearings, which help support increased precision even under high speed and high loads. Dynamic motors and high-precision gear units which support short turning times also allow for improved speed and accuracy.
The interfaces between the positioner and the workstation also need to be considered. For point-to-point positioning (open-loop), positioners may include multiple-stop mechanical or solid-state limit switches on its axes. For closed-loop positioning with feedback to controls, DC servo-drives may be integrated into the positioner.
Such controls are also essential because some workstations require the use of two or more positioners, each of which does various tasks, and needs to be coordinated with the others. Integrating multiple positioners into one system allows increased efficiency, since loading and unloading times can be reduced.
Modern positioners may include software controls and sensors which can automatically compensate for factors like load weight and balance, gravity, inertia and friction for improved speed and accuracy.
Types of positioners
Positioner technology is constantly evolving, with many novel form factors catering to different automated applications of varying precision. For example, in the nano-technology space, six-axis robotic parallel positioners with simultaneous operation of the six actuators allow sub-micron or nanometer-precise motion patterns in 6D vectors.
While increasing the number of axes means improved dimensional control of work pieces, it also means increasing complexity during the commissioning and calibration phases, and an increased investment into the solution, so choosing the right positioner type for your needs is critical.
Headstock and tailstock positioners rotate long work pieces around a horizontal centreline. These can be used to turn long and complex work pieces to allow the robot to more easily access the required areas. Three-axis variants provide two rotational axes and one main sweep axis.
The systems are usually made up of a powered headstock frame with a rotation motor, a table which holds the work piece, and the unpowered tailstock frame. Their heights and speed can be adjustable using the control system. They are ideally suited to welding, flame cutting, flame-spray and cladding operations.
Ferris wheel positioners allow the robot to weld on one side of the table, while the operator or another robot loads and unloads parts from the other. The continuous operation allowed by this sort of positioner decreases downtime.
Turntable positioners rotate a workpiece around a vertical axis, and are used for welding, flame cutting, flame-spray, grinding, X-ray or drill presses. Some turntables include a barrier which runs through the middle. The robot operates on one side of the barrier while the operators load and unload pieces on the other side for uninterrupted work.
Two-axis variants of the turntable provide tilt as well as rotation, and are also called drop-centre and tilt-rotate positioners. Five- or six-axis types provide additional degrees of freedom, in accordance to application needs.
In addition to moving and positioning work pieces, robotic transporters can be used to move the robot around the work piece. These are typically used in applications where the work piece exceeds the maximum work envelope radius of the robot. Transporters can be cost-effective because they reduce the number of robots required for larger works.
When choosing robotic transporters, consider the dimensions and configuration of the job at hand, the way parts flow into the work cell, the supporting structures needed for the robot, and safety issues to do with the interaction between workers and machinery.
Linear floor tracks: robots are mounted on a carriage, which moves along tracks lined on the floor. This is a flexible and cost-efficient solution, but requires a lot of floor space.
Wall-mounted tracks: allows robots to work from overhead, but requires additional support structures, which can increase cost.
Linear gantries: suspending the robot overhead, this approach allows additional axes to improve the reach of the robot. These can be expensive due to the overhead structures required as well as additional control systems.
Radial gantries: another overhead robot transporter approach. Uses a rotary base, with the robot attached to a fixed length boom. Radial gantries can be used in addition to positioners to improve flexibility.
Many robotic and automated systems come as a turnkey solution. Be sure to talk to your vendor about your specific application needs, and consider possible expansion options, in order to choose the right positioners or robot transporters to enable the precision and cost-savings associated with automation.