This application looks at how Contrinex’s tiny Ø3mm inductive sensors, available from PLUS Automation, ensure a robot gripper can reliably pick up fragile silicon wafers without damaging them.

A photovoltaic cell manufacturing plant handles a large number of fragile silicon wafers using a high level of automation. One such automation is the use of compact two-finger robot edge-grippers to transport trays of silicon wafers between operations. To avoid impacts on the wafer’s surfaces, process engineers require reliable confirmation that the gripper’s jaws are fully open before the gripper descends to pick up a tray. 

Customer application

A typical photovoltaic solar panel consists of an array of 100+ silicon wafers, so their manufacturing involves handling and placing a very large number of thin and fragile silicon wafers. The high levels of cleanliness, high volumes and repetitive nature of the assembly lead to extensive, fast-moving automation.

In the panel assembly area, robotic systems handle the silicon wafers, position them on the panel, assemble and wire the panel and present it for automated testing. The silicon wafers are transported to the panel assembly area in trays which are picked up by compact two-finger robot edge-grippers. These grippers were prone to damaging the wafer’s surface if the gripper malfunctioned or was inaccurate.

Analysis showed that open/close errors accounted for a significant proportion of the gripper malfunctions which led to scrap being produced. The primary issue was that on occasion the jaws only partially opened causing the fingers to impact and damage the surface of the wafers. A cost-effective solution was therefore required to prevent the robot from attempting the pick operation if the jaws were not fully open.

Customer solution

Contrinex offers a very large choice of inductive sensors, perhaps the largest in the industry and at one end of the size criteria are their tiny Ø3mm inductive proximity sensors. Despite their diminutive size, they offer the high performance and reliability Contrinex is renowned for, with for example a 1mm sensing range, a V2A stainless-steel housing with an LED indicator, up to 3,000Hz switching and IO-Link connectivity included in a sensor which is only 22mm long.

Two of these inductive sensors are mounted above the two top faces of the gripper fingers to sense their presence when the jaws are in the fully open position. This verification of the jaws being open eliminates the risk of scrap being caused by partially open jaws impacting the wafers.

These miniature inductive sensors are popular with robot and gripper OEMs and system integrators because of their small size, high performance and reliability, which offers a fit-and-forget solution. Even including a 2m long robust PUR sheathed cable, the whole sensor weighs only 25 grams, with the cable contributing the majority of the weight. Therefore, fitting them to small grippers adds only a very small (Ø3mm x 22mm) sensor with a small additional mass.

Contrinex offers a variety of shapes and sizes of miniature inductive sensors, for example as small as Ø3mm, M4 and cubic 5x5mm.