Silicon solutions powering the Robotic Future
Clemens Müller is Director Business Development Robotics at Infineon and outlines how compact power solutions will change industrial robotics.
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The world of manufacturing is changing, driven by closely coupled, internetworked robotic solutions and Industry 4.0 initiatives. Sequential processing of goods, conveyor belt-style, is being disregarded in favor of more flexible autonomous production islands, with self-powered robots delivering the work-in-progress to, and collecting it upon completion from, robotic work stations. Simultaneously, industry is being encouraged to use power more efficiently. This is measured at plant level, requiring that individual subsystems, such as robots, their drives, charging systems of mobile autonomous robots, and power distribution and delivery, need to contribute their part.
Industry 4.0 cannot improve power efficiency alone
Silicon solutions for power systems and drives continue to improve in efficiency, even when staying with well-established silicon-based technologies. This, coupled with the resulting significant reduction of heat loss, and packaging of ever decreasing dimension, enables robotic systems designers to consider completely new ways of designing their products.
The control systems of a typical industrial robot place the power and control system external to the arm of the robot, requiring that power is delivered to its actuators via cables threaded through the body of the robot itself. The effector attached to the robot then requires its own additional wiring harness linked back to its power and control system. But, together with actuators and transmissions, power and signaling cables are the robotic subsystems with the highest likelihood of failure.
This could be improved in the future by fitting the drive solutions directly to the actuators. This would enable a single cable harness to be used for power distribution to all the actuators. A further consideration could be to use this power harness for communications, utilizing power-line communication technologies, thus saving further wiring and another potential source of failure. With such an optimized cabling harness in place, the possibility opens up to provide power and control to whichever effector is being attached to the robotic arm.
Such high levels of integration are made possible by the compact and efficient discrete MOSFET power switches that are available today. Supporting voltages up to 650 V and power under 5 kW in increasingly small packages, the CoolMOS family of superjunction MOSFETs are one example. Available in a TO-Leadless (TOLL) package, with a 30% smaller footprint when compared to a typical D2PAK packaged device, its grooved leads leave it easy to visually inspect during production. This also leave designers with just a 1 nH package inductance to consider, alongside the impressive 33 mΩ RDS(on).
Integrated gate drivers simplify circuit designs
Compact motor inverter gate drivers are also demanded that can also keep the bill-of-materials (BOM) count low. The 2EDL family of EiceDRIVER devices complement both discrete MOSFETs and IGBTs in half-bridge applications. Based upon silicon-on-insulator (SOI) technology, these devices are inherently resistant to transient voltages. As there are no parasitic thyristor structures present in the device, it is protected from temperature and voltage dependent latch up.
They also feature a range of innovative capabilities that would otherwise require several discrete semiconductors together with complex microcontroller programming algorithms or features. For example, integrated filters suppress unwanted, EMI-induced short pulses at the inputs, while filters in the supply monitoring circuitry handle voltages spikes for high-side and low-side undervoltage lockout. When used together with IGBTs, an asymmetric undervoltage lockout is implemented. Deadtime is also handled automatically, while an interlock function stops simultaneous activation of the two outputs.
Infrastructure investment benefits from Industry 4.0
Whilst the conveyor belt approach to manufacturing delivered many efficiencies in production, today’s demands for product customization and differentiation in a crowded market requires a more flexible approach. Increasingly, autonomous guided vehicles (AGV) are being used to shuttle work-in-progress to work stations that can apply their unique work step. Their ability to move around requires them to have their own power source, typically batteries, which need be charged. During times of low activity, or when energy is low, AGVs can reattach themselves to a charging point until ready to undertake their duties again.
To stem the huge energy demands required during production line start-up, and to cover periods of power loss, uninterruptable power supplies (UPS) are an integral element of any manufacturing facility. But, with masses of energy storage available in the batteries of the AGVs, it is perfectly reasonable to assume that these devices could be used to complement the UPS needs of the factory in the future. Industry 4.0 and internetworked systems provide the key here to an additional potential saving in infrastructure investment.
SiC-based diodes deliver efficiency improvements
To enable this approach, AGVs will not only need to be capable of charging from AC outlets, but also generating AC to inject back into the electrical network. This can be achieved using a combination of a bi-directional, zero-voltage switching (ZVS) phase shift full bridge (PSFB) DC-DC convertor, coupled with a totem pole continuous-conduction mode (CCM) power factor correction (PFC) solution. Here, as before, low-losses are essential to ensure optimal efficiency. Silicon carbide (SiC) is providing opportunities to achieve these savings when compared to more traditional silicon solutions. SiC is ideally suited to high-voltage, high-power and high-temperature applications due to its remarkable electronics properties. These include a wider band gap, larger critical electric field, and higher thermal conductivity than silicon-based semiconductors.
Such devices offer extremely fast turn-on times, making them ideally suited for the high switching speeds employed in PFC circuits. In turn, dynamic losses can drop considerably in typical topologies. The CoolSiC family of Schottky diodes are one such example of a product to be considered. With no reverse recovery charge, these devices offer low turn-off losses. When coupled with MOSFET or IGBT switches they lead to a reduction in turn-on loss. Their increased efficiency also results in lower thermal losses. As a result, designers can increase power density, leading to smaller volume power solutions and reduced cooling requirements.
Industry 4.0 is, at last, starting to become more tangible in the world of manufacturing. Networked robots, feedback from sensors, and data from autonomous manufacturing islands can all be monitored and coordinated from a central system. Such networks even allow individual system elements to communicate with one another to make autonomous decisions. However, enhancements in power delivery and distribution, as well as power savings, will not come from improved connectivity alone.
New architectures for robots, utilizing compact, energy efficient silicon solutions, will provide energy savings along with improved reliability, as cable harnesses reduce in complexity and weight. The stand-by power provided by on-site UPS systems can also be newly dimensioned, especially if the mobile battery power of AGVs can be coordinated to participate in the power delivery mix. AGVs will also be capable of longer working times and shorter charging times, thanks to more efficient silicon and silicon-carbide power solutions, as well as resulting from the weight and size reductions these devices make possible.
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