2012

Solar Cell Manufacturing and Robot Automation: Right Fit, Right Robot

Major Robot Types

Robot kinematics can be divided into four major categories: Cartesian, SCARA, Articulated, and Delta/Parallel.

altCartesian -- The Cartesian kinematic solution is highly configurable as the platform includes everything from a single degree of freedom or unidirectional travel, to numerous axes of motion. Given the simplicity of this kinematic, adjusting strokes or lengths and configuration are relatively easy when compared to this model’s counterparts. Multiple drive trains exist that are optimized to provide high throughput or precise motion as characterized by whether the drive might be a ball screw or a belt-driven mechanism. Platforms exist that accommodate small-part assembly to extremely large part transfer such as overhead cranes that might be observed in a manufacturing facility.

Cartesian solutions have numerous applications within the PV industry. They can be applied to both small and large workspaces. Cartesians are typically called upon to serve applications where the substrate remains in the same plane. This is to say that if you were to pick a product off of a table or a conveyor, it does not need to be flipped or change its configuration other than a rotation in the same plane as the table or conveyor (X-Y plane). An example of a job using a small Cartesian might be dispensing sealing material on the flange of a junction box. The sorting and placement of solar cells in a large rectangle is also an optimal application for a Cartesian solution. Solar cell sorting into multiple stacks in a large work area and processes such as stringing up and layup within a large cubic area where robots are required to reach with good repeatability are optimum applications for Cartesian.

SCARA -- SCARA stands for Selective Compliance Assembly Robot Arm. It offers a cylindrical work envelope and this category of robot typically provides higher speeds for picking, placing, and handling processes when compared to Cartesian and articulated robotic solutions. They also deliver greater repeatability by offering positional capabilities that are superior in many cases to articulated arms. This class of robot is used for lighter payloads in the sub-10-kilogram category for applications such as assembly, packaging, and material handling.

Within solar manufacturing processes, these robots are best suited for high-speed and high-repeatability handling of cells in smaller workspaces. Where the workspace is constrained sufficiently, the SCARA is an excellent selection. For example, junction box handling and assembly of panels are good applications for this robot group. Stringing is a process that, with its increasingly tight tolerances, is unmanageable with manual labor. As wafers migrate to thicknesses of 150 micron and thinner, the propensity for damage is greatest when labor is applied. As wafer thicknesses decrease over time as forecasted, the thermal expansion of the silicon will also become an issue while soldering. So it’s going to become increasingly important to maintain yields in stringing by controlling and automating the soldering operations, even in low-cost labor markets, through the use of mechanisms such as SCARA robots.