SEW-EURODRIVE Offers Contactless Energy and Data Transfer System

Although robotic systems are sometimes limited by constraints in automation and drive technology, this issue can be easily minimized. Application-specific automation from a single source enable machine builders to develop new, commercially beneficial solutions for customers. To demonstrate, consider the case of a gantry robot that uses contactless energy and data transfer instead of fixed wiring runs and cable carriers.

Gantry robots are a tried-and-tested solution for intralogistics material flows within a machine or application. They are commonly used to detect products automatically, grip them securely and quickly, and take them to their destination. This type of robot is useful in many industries, and can be used for a wide range of product sizes and weights, and distances to be covered. Oftentimes, the lengths of power and communication cables and cable carriers limit the flexibility and adaptability of an existing machine to a new production scenario. Adding contactless energy and data transfer opens up new production scenarios, and has largely consigned cables to the past.

Less noise, enhanced dynamics, greater flexibility

The illustrated solution demonstrates contactless energy and data transfer combined with intelligent software and reliable mechatronics to create a fully integrated solution. What immediately catches the eye about this gantry is the drive concept used to move the gantry robots on the rail: contactless energy transfer. As a result, multiple robots can move freely on the same horizontal stretch, greatly increasing the flexibility of this gantry robot application. This regularly leads to overlapping sections between robots– ultimately offering a great deal of freedom in terms of machine design and operations. Logistics processes of this kind would not be as easy to implement with cable carriers, because of the additional area that carriers use along the entire distance of the system. In addition, cable carriers generate noise, are subject to wear, increase inertia, and have an overall negative impact on both dynamics and energy efficiency due to the friction they generate. Another benefit of contactless energy and communication transfer is that there are no longer any restrictions regarding installation space, cable breakage or limited cycle rates – issues all associated with cable carriers and moving cables. The clever innovation is made possible by a contactless inductive energy transfer system, including a decentralized power supply module. Depending on the design, this module delivers a transmission power of between 5 and 11 hp.

What is exciting about this logistics solution is that throughout the entire load cycle, the robot consumes less than 0.7 hp via the pick-up – even though the horizontal axis alone requires more than 5 hp of acceleration power during acceleration. The short-term energy requirements are met by the energy storage unit, a double-layer capacitor package that takes care of the primary energy supply to the robot with a DC link voltage of 100 V. The typical travel profiles of a gantry robot, which involve alternating acceleration and braking phases, led to the idea of retaining the regenerative energy generated during braking within the process instead of dissipating it via resistors. The energy storage unit absorbs this braking energy and additionally functions as a booster when the gantry's drives accelerate at 20 ft/s2. The design is so effective that the contactless energy transfer and storage solution only has to compensate for the system's mechanical efficiency losses, which amount to around 0.7 Hp. Unlike the familiar DC link connection of multi-axis applications, which is located in the central control cabinet, each unit is enabled to store energy independently. This makes it easy and convenient to scale this type of system.

Cable-free communication

The robot gantry's contactless energy transfer system, which eliminates the need for restrictive cables, also extends to the communication processes. In this context, an EtherCAT data light barrier transfers the interpolated position setpoints from the central motion controller to the four servo inverters in the moving housing box at 1 ms intervals. A motion controller calculates the complex robot motion control – and can do so for up to four robots at once. Motion control involves performing calculations to prevent collisions and coordinating the robots to achieve a productive overall system. If a machine in a production network requires double the material flow output, the gantry system gives users the option to move a robot from another section on a flexible basis. Handling units that draw their power with cables, in contrast, are tied to their section. As a result, the associated resources become movable and systems as a whole are more flexible and productive. Entirely new machine concepts can be created based on this approach. The demands placed on communication are correspondingly high as well.

Optical real-time communication

The automation provider opted to use the real-time Ethernet protocol EtherCAT in the gantry – once again dispensing with cables by implementing an optical connection to the mobile units. The drive data can be delivered to the robots via data light barriers. Having separate motion controllers in each robot is a thing of the past: one does the job for running the whole robotic system. With each cycle taking 1 ms, the optical system has practically no latency periods when transmitting the interpolated position setpoints to the inverters or feeding back the relevant actual values.

Communication for the functional safety technology works in the same way. For this application, a central safety controller for all robots and the machine as a whole was selected. This safety controller communicates directly with the MOVI-C automation controller via EtherCAT using the EtherCAT FSoE (Fail Safe over EtherCAT) protocol. This setup enables both controllers to share data with ease, simplifies programming considerably, and offers excellent conditions for diagnostics and debugging thanks to its high information density.

Solutions in a nutshell

The seamless integration of the FSoE safety master and the EtherCAT data light barrier are integrated into a comprehensive automation solution including motors, electronics and visualization. Clearly, working with a skilled automation provider can streamline the development process and the newest drive technology innovations and trends can be considered. In this context, standardized interfaces play just as important a role as prepared software modules or application-specific function modules.