Creating a robot for small parts handling calls for a machine design that is both highly dynamic and extremely precise. With the Galileo Sphere, the Italian Mechatronic System Company has built a robot that combines the advantages of linear and direct drives in one system. The curved linear motor at the bottom (Teta 2) enables full rotation of the robot, while the second linear motor (Teta 1) lets the robot arm pivot by more than 68°. The actual arm (Z1, Z2) is made up of two iron-free linear motors, each moving one carbon rod on which the wrist joint (Teta 3) is attached to the gripper. The gripper consists of a vacuum sucker that can be rotated around its axis using a compact motor, an arrangement allowing five degrees of freedom.
The main feature of direct drives is the elimination of the kinematic chain between motor and load. This offers several advantages, such as low tolerances and friction losses as well as increased reliability at lower costs. Some systems for handling robots, based on parallel kinematic arrangements, can move parts with up to 2 kg in a cylindrical work area of approximately 1 m in diameter and 25 cm in height. The prototype for the Galileo Sphere involves a work area with a diameter of 1.87 meters and a height of 45 cm, which results in a potential working volume of nearly 1,000 liters for moving parts with up to 6 kg at a rate of 80 cycles/min. These characteristics make the robot suitable for applications in the areas of assembly, material handling, packaging, and sorting. Parallel kinematic arrangements, also known as a “Stewart platform” or hexapod, feature a high level of dynamic capability and rigidity, which leads to a high degree of positioning and repeat precision. However, the disadvantage of this type of system is a limited working area and high complexity. The Galileo Sphere combines the dynamic properties of parallel kinematic arrangements with the wide scope of anthropomorphic robots.
Galileo’s configuration was chosen based on three main ideas: A polar system provides a large work area and is well suited for the use of curved linear motors; these motors use an optical linear encoder with a precision rating of 1μm; this sensor is also the factor that determines maximum motor size as well as its precision. A corresponding control solution, the ACOPOSmulti drive system from B&R Industrial Automation Corp., Roswell, Ga., was chosen for the power and performance of the robot’s specialized motors. An automation PC handles central control and visualization. Data exchange with the drives and to the necessary input and output modules occurs via Powerlink in a cycle time of 400μs. Integrated safety technology ensures operator safety during commissioning, maintenance, and operation.
Control software flexibility was also important to the robot’s design. B&R’s integrated software concept provided the platform required: Functions for controlling the robot’s movements work in unison with PLC functions such as gripper control. This makes it possible to perform movement sequences and switching functions quickly and to process working cycles as fast as possible.
An open interface for kinematic transformation functions makes it possible to combine a robot with a path controller without having to change core components on your own. The path controller is provided with a new transformation module in the form of a software library that is used in path design, dynamic calculation, and path interpolation. For more information, visit www.br-automation.com.