Many design points go into electric vehicle (EV) battery assembly cells that ensure high reliability and repeatability, optimum overall equipment effectiveness, maximum throughput, and Industry 4.0 concepts of digitalization. Examining an EV battery degassing automated cell that is widely installed across the industry exemplifies many of these design features.
Forming refers to the initial charging and discharging process for cylindrical, prismatic, and pouch types of EV battery cells. The charging process generates gas within each battery cell. Gas must be extracted from the sealed battery cells without losing electrolyte.
From the forming racks, battery cells move to an automated degassing system. Vacuum grippers typically lift the battery cells out of trays and onto the degassing system. A cantilevered handling system picks and places the battery cells into and out of a degassing chamber. These last two operations are pick and place, a method common throughout the EV battery cell production process.
Inside the chamber, pneumatic cylinders move hollow lances that pierce the battery cells and, using vacuum, evacuate the gas until the electrolyte enters the lance. The system then switches from vacuum to positive pressure and blows the electrolyte back into the battery cell. The production unit seals the battery, which is typically done by thermal or ultrasonic welding. Degassed battery cells are picked and placed out of the degassing chamber and put back into trays. Trays packed with battery cells move to the next production stage.
The automated degassing cell features both pneumatic and electric motion. Why use both electric and pneumatic? Each type of motion has its strengths, with pneumatics being the more economical and simpler of the two. Pneumatics lowers the total cost of the automated system and simplifies aspects of the system, allowing faster commissioning, installation, and troubleshooting.
Design Considerations for Degassing Cells
Electric actuators provide a more reliable means of synchronizing the motion of the plates used for sealing the battery cells. Synchronized motion ensures there are no alignment issues from one plate arriving before the other. This level of control makes the accuracy and timing of electric actuators the optimal solution for this aspect of the operation. OEM designers identify where simpler and less expensive motion is best and where electric precision is mandatory to create the most cost-effective system for the end user.
While hundreds of degassing cells are operating today, designers are required to design each for its specific application, type of cell, environment, and production requirement. In their design considerations, correct sizing of electric and pneumatic components is essential for achieving two goals — cost effectiveness and meeting functional requirements.
Over-engineering through incorrect sizing amplifies complexity, increases commissioning time, and creates troubleshooting challenges. Look for engineering productivity tools from suppliers that harmonize all the components; for example, drive, motor, and actuator, or cylinder, switch, fittings, and tubing. These tools not only speed up design but also size the system correctly.
The battery degassing cell’s cantilever handling system is based on spindle axes. These axes ensure dynamic and safe loading and unloading of the degassing chambers. The cantilever design, which is situated directly over the work envelope, minimizes cell footprint. Cartesian pick and place systems rarely require guarding; the elimination of guarding also reduces footprint.
A Cartesian system is ideal because most battery cell handling is pick and place in the X, Y, and Z axes, exactly what the Cartesian system is designed for. These pick and place systems deliver high accuracy over the entire work envelope, an advantage compared to six-axis robots, which lose accuracy at the periphery. Cartesian pick and place systems are also less expensive than articulated robots.
During the degassing process, a pinch valve evacuates the process chamber. Pinch valves are compact, durable, energy-efficient, easy to maintain, and flexible. While a pinch valve might not be the first valve that springs to mind for controlling air flow, they offer a cost, size, and functionality alternative to other valves, such as diaphragm or ball valves. The point is to identify the optimum component, which may not be the obvious first choice. Lean on suppliers to suggest these kinds of not-so-apparent solutions.
Decentralized I/O System
The degassing cell features a decentralized I/O system. Decentralized I/O integrates all I/O and IO-Link devices, such as sensors and valve terminals, into the communication network of the plant, creating seamless communication from the workpiece to the cloud.
Decentralized I/O is flexible, compact, lightweight, and provides real-time capability and is essential for the deterministic behavior of the equipment. Decentralized I/O offers a simple structure that supports the digital factory and provides high scalability where additional I/O points are easily added.
Without decentralized I/O and IO-Link master, end users would find it more difficult to scale and increase I/O points after the initial design. If the control architecture is not decided on from the start of the design, consider standardizing on an I/O architecture that can easily shift between platforms. This added flexibility will result in the I/O schematic and physical layout not having to change. The only change will be the interface module that connects to the PLC. Additionally, if the control platform is not set, choose motor controllers that support multiple protocols.
The degassing cell includes a soft adaptable gripper for picking and placing battery cells into and out of the degassing chamber. Gripper conformance to the workpiece means the battery cell is secured without excessive force. In this regard, designers commonly use vacuum for pouch and cylindrical cells. Vacuum generation should be very close to the suction cup to increase efficiency by using less vacuum and lower energy consumption. A pressure sensor integrated into the vacuum generator can verify if the cell is still being held after the move. Depending on the cell, magnetic grippers are sometimes an efficient option.
The design engineer must consider what happens during an emergency stop situation to ensure the battery cells are not dropped. Built-in gripping redundancy is a must. Vacuum grippers are often paired with a mechanical fail-safe positioned below the battery cell, for example, a finger clamp.
The wonderful thing about battery cell handling is that all the technology for motion, control, and communication is both available and proven. OEMs using these key considerations can design and deliver fast-to-commission, reliable, and supremely efficient systems.
This article was written by Lawrence Lin, EV Batteries Business Development Manager, and Jarod Garbe, Automotive Industry Segment Manager, both at Festo (Islandia, NY). For more information, visit here .