In most assemblies that are joined with threaded fasteners, the cost of the fasteners is not as important as the cost of installing them. Automation is one way to control that cost.

Recently, an appliance manufacturer in Poland wanted to increase throughput and quality on the line that assembles doors for washing machines. Specifically, the process of installing screws to secure a glass window in the door had become a bottleneck. Engineers wanted to automate the process. 

Qbig, a systems integrator in Lodz, Poland, got the job. “Assisting people with robotics for a monotonous and tiring job such as screwdriving allows resources to be freed up and an employee to be used in more valuable task,” says Bartosz Luczak, co-owner of Qbig. “Robots increase the productivity of the plant by reducing the screwdriving cycle time.”

Automating the screwdriving process freed up skilled labor to perform other tasks. Photo courtesy Kuka

The appliance manufacturer placed a high priority on cycle time. This was quite a challenge during the design phase of the screwdriving project. Qbig engineers considered several options.

One option would be to fixture multiple autofeed screwdriving spindles together and mount them to a linear slide. The door would stop below the screwdriving station; the slide would come down, and all the fasteners would be installed simultaneously. This option was ultimately rejected for its relative lack of flexibility.

Another option would be to mount a single autofeed screwdriver to a robot. The door would stop at the screwdriving station, and the robot would install each screw one at a time. This option was more flexible, but stopping the door meant the station couldn’t meet the cycle time requirement.

It was then that Qbig engineers came up with a unique way to shave a few seconds off the cycle time: screwdriving “on the fly.” The door would still stop at the station, at least initially. However, as the last fastener is being driven, the door begins moving out of the station, freeing up space and allowing the next door to enter, stop and position itself, so the robot can begin installing screws immediately, without having to wait.

For a conveyor-tracking application, a six-axis robot was the best option. Photo courtesy Kuka

For this design, a six-axis robot was the best option. Qbig engineers chose the KR Agilus robot from Kuka to do the job. The KR Agilus is a compact six-axis robot for particularly high working speeds. Maximum payload ranges from 6 to 11 kilograms, and maximum reach ranges from 706 to 1,101 millimeters. Positional repeatability ranges from ±0.02 to ±0.03 millimeter.

The robot can be mounted to the floor, ceiling or wall. It is ideal for confined spaces thanks to its integrated energy supply and control technology. Safe robot functionality enables innovative automation concepts. The robot is protected against electrostatic discharge, and variants are available for clean rooms; hygienic or wet environments; and potentially explosive environments.

Thanks to its lifetime lubrication, the robot never needs a change of lubricant in the gear units and has minimal maintenance requirements. 

For screwdriving on the fly to work, Qbig engineers needed a way to precisely determine and control the position of the moving components to ensure the fastener is installed correctly. Kuka’s ConveyorTech software solved that problem. The software coordinates interaction between the robot and conveyor. The software automatically adjusts the robot’s movements to the linear motion of the assembly line.

ConveyorTech software automatically adjusts the robot’s movements to the linear motion of the assembly line. Photo courtesy Kuka

The software is simple to program and fast to commission. The software makes it possible to work parallel to the progress of the conveyor. The software works with belt conveyors or with automated guided vehicles. It also offers the option of multiple tracking. Up to five conveyors can be monitored without difficulty. Both linear and circular conveyors can be monitored in mixed operation. In addition, up to 1,024 components per conveyor can be managed in memory.

“We didn’t realize that there was such an application as ConveyorTech,” says Luczak. “We knew that it was possible to track and control packages on the line, for example, but we were not sure if this tracking was accurate enough to be used with a screwdriving application. At first, we had doubts, but in the end the software solved our problem.”

Thanks to conveyor tracking and robotic screwdriving, Qbig was able to meet the appliance manufacturer’s cycle time requirement.

For more information on robotics, read these articles:
Robots Automate Tough Automotive Assembly Project
Vision-Guided Robots Process Hydraulic Components
Kuka Introduces New High-Payload SCARA