2012

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

altArticulated Robots – Articulated robots have a spherical work envelope. These arms offer the greatest level of flexibility due to their articulation and increased numbers of degrees of freedom (DOF). This is the largest segment of robots available on the market, and therefore offers a very wide range of solutions from tabletops to very large 1000-kilogram-plus solutions. Articulated robots are frequently applied to process-intensive applications where they can utilize their full articulation and dexterity such as welding, painting, dispensing, loading, assembly, and material handling.

Articulated robots are applied to a wide variety of solar applications. Examples include handling heavy silicon ingots that are also in an area where the robots might require industrial protection, and handling wafer cassettes where the orientation of the carrier might differ from pick to place utilizing the full dexterity of the robot. Handling glass, subassemblies, and assemblies where the products are introduced to the cell in a different configuration than they are presented to the system again take advantage of an articulated arm’s flexibility. Articulated robots permit the optimum introduction of product into a cell that may be in a vertical orientation to maximize floor space while the assembly process is most efficient in a horizontal orientation. Edge trimming and module assembly where tool change and other process considerations dictate the use of articulated arms is yet another use of this class of robots within the PV manufacturing process.

altDelta/Parallel Robots -- This kinematic solution provides a cylindrical work envelope and is most frequently applied to applications where the product again remains in the same plane from pick to place. The design utilizes a parallelogram and produces three purely translational degrees of freedom, driving the requirement to work within the same plane. Base-mounted motors and low-mass links allow for exceptionally fast accelerations and therefore greater throughput when compared to their peer groups. The robot is an overhead-mounted solution that maximizes its access but also minimizes footprint. These units are designed for high-speed handling of lightweight products, and offer lower maintenance due to the elimination of cable harnesses and cyclical loading.

Parallel robots are deployed into many solar cell processing steps. Again, they offer high-speed transfer of solar cells through manufacturer lines and a multitude of processes. Three examples are diffusion of process equipment, wet benches, and PECVD anti-reflective coating machines. In these applications, the tables and trays have large placement opportunities that could be equally serviced by a Cartesian; however, the parallel robot outperforms the Cartesian from a throughput standpoint.

Robot Comparison Example

Following is a comparison of the four robot categories when considering their use in an anti-reflective coating load/unload process. If we look at a Cartesian robot, it is optimized from a reach standpoint. However, the majority of solutions here would prove too slow and would require in excess of a single-head EOAT. This complication would drive the need for pre-alignment and further complications in pre-conditioning the product, and therefore may prove a Cartesian solution to be considered less flexible.

SCARA robots would give increased speeds and prove more flexible than a Cartesian. However, if we look at a traditional tabletop version, it would limit the workspace and therefore may not be optimal in reaching all points on the load and unload areas of this machine.

Articulated robots are too slow for loading/unloading with single-head EOAT, and a spherical work envelope isn’t ideal for covering pallet/matrix.

Therefore, a delta or parallel style robot might be optimal for a number of reasons. First, the overhead mount is ideal in reducing the footprint of the automation cell. And when we combine the benefits of the delta with vision, it provides a flexible solution that will meet the throughput requirements. As noted below, vision is an enabler not only for parallel linked robots, but also for all categories of robots.

Flexibility with Vision

Vision has become a highly adopted tool to improve the productivity of robot automation in all industries and all facets of placement. Vision systems offer tremendous flexibility for applications that don’t require fixtures or trays for part location. Vision-guidance is a feature that allows the vision system to take a picture and compute a part’s location and orientation, and guide the robot to the part using a computed robot-to-camera transformation obtained through an automated calibration process. It allows tremendous flexibility and cost savings because parts don’t have to be fixtured. Parts can be randomly presented to the robot without pre-orientation or alignment, or put into a tray, which also reduces cost.

These systems frequently incorporate line tracking, which enables the robot to pick these parts from a moving belt, further optimizing the production process. Robot-integrated vision allows inspection to be incorporated into the handling process. This puts the inspection or quality control process in parallel with handling, further reducing the overall cycle time and increasing throughput. Different part geometries only require vision re-training or the selection of a recipe instead of manual changes in fixtures and tooling. This increases the overall lifetime profit of the equipment by virtue of its optimization and improved throughput. Most robot manufacturers offer packages with multiple cameras and tracking solutions for integration into a single cell. This offers tremendous power and flexibility for solar manufacturing.

History has shown that automation has played a significant role in reducing manufacturing costs in many industries, and when the costs associated with higher quality and yields are considered, the benefits of automation offer an even more appealing value proposition.

This article was written by Rush LaSelle, Vice President and General Manager of Mobile Robots at Adept Technology, Pleasanton, CA. For more information, visit http://info.hotims.com/40430-121.