Precision Robotics and Automation: Hexapods Advance Production Processes

There are two methods of constructing multi-axis positioning systems: serial kinematics and parallel kinematics. Stacked serial kinematic systems are easy to design and control. However, there are a number of drawbacks compared to the more powerful and elegant group of parallel kinematic machines.

Parallel Kinematics and Their Advantages

Each actuator in a serial-kinematic multi-axis system is assigned to exactly one degree of freedom. When position sensors are integrated, they are also each assigned to one drive and only measure the motion on the corresponding positioning axis. Any undesirable motion in the other five degrees of freedom, which for example, occur as a result of guiding errors of the individual axes, cannot be detected or compensated. Contrary, in a Hexapod, all actuators directly drive the same platform. The accumulation of drive train and guiding errors – common with stacked systems – does not occur with well-designed parallel kinematics.

For example, unlike with serial kinematics, if you want to move a platform in just one axis, the controller has to change the individual lengths of each strut – some will extend and some will contract. The required coordinate transformations and path calculations need a powerful controller capable of running 100’s of thousands of operations per second, because there is no linear dependence on the current coordinates. The stiffest mechanical designs are based on cardanic joints with an offset between the axes, making the math even more complex.

An essential feature of the Hexapod system allows the adaptation of both the position and the alignment of the reference coordinate system and the pivot point by simple software commands.

To adapt the trajectory perfectly to the requirements of the application, work and tool coordinate systems can be defined referring to the position of the workpiece or tool. This function saves valuable time in industrial automation and photonics alignment tasks.

Hexapods can carry loads up to 2 tons at any orientation and if required, be mounted upside down. Because the maximum permissible load of a Hexapod system depends on various parameters, such as the mounting position, the center of gravity of the load and the current position, suitable simulation programs are supplied that enable convenient set-up. They also allow easy determination of workspace and motion limits depending on the selected center of rotation or the current position.

Fast Motion and Scanning

Motion simulators make high demands on motion dynamics. They repeatedly perform defined motion cycles, for example, for quality assurance and function monitoring of products in mobile use. Typical examples for this include inspection systems for acceleration or gyroscopic sensors, like those used in smartphones, cell phones, and cameras for detecting changes in position. They are tested by means of a specified motion pattern.