Given their small size, high production volumes and exacting precision requirements, these sensors are not assembled manually. Automation is the only way to go.

An important and challenging part of the assembly process is attaching the sensor to a carrier. The carrier helps to integrate the sensor into various systems, whether it’s for physical mounting, environmental protection, or network connectivity. 

The sensor is often attached to the carrier using a wave-soldering process. Ideally, the height of the solder wave should be consistent. However, molten solder, like any liquid, can be unpredictable. Slight variations in height are unavoidable, and that means the height of each carrier assembly as it passes over and through the wave must be adjusted on the fly.

This was the challenge faced by manufacturing conglomerate Erwin Quarder Systemtechnik GmbH & Co. in Espelkamp, Germany, about 60 miles west of Hanover. 

Founded in 1971 by engineer Erwin Quarder, the company began as a manufacturer of tools for stamping and injection molding. Over time, the company began adding complementary services. As long as we’re making the mold, management reasoned, why not make the parts, as well? And, if we’re making the parts, why not assemble them? The company’s automation division grew out of the need to make equipment to do just that.

For the automotive sensor, Erwin Quarder Systemtechnik designed and built a fully automated production system that begins with the molding of the parts and ends with finished sensors. The assembly line incorporates multiple processes, including insertion of the sensor onto a carrier, fluxing and soldering, test and inspection, and finally placing the finished assemblies into trays. 

Photo courtesy Denso Robotics

Robot Adjusts on the Fly

Six-axis robots from Denso Robotics are the workhorses of the system. For example, a Denso VS 6556G robot plays a key role in the wave-soldering process. The robot is equipped to carry a custom soldering fixture that holds four sensor assemblies. In a precise motion, the robot must pass the fixture over and through the solder wave.

The task is more difficult than it sounds. Although the height of the solder wave is set at 4 millimeters, the actual height of the wave can deviate by as much as 1 millimeter. As a result, if the height of the fixture remains constant, some assemblies could get too little solder and some too much.

To prevent that from happening, a sensor continually monitors the height of the solder wave and reports that value to the robot controller. This enables the robot to adjust to the position of the fixture on the fly so it’s always at the ideal height for soldering.

The soldering process must be as precise as possible, to prevent damaging the sensors or deforming the carriers. Once the soldering process has been completed—it takes 30 to 32 seconds per fixture—the robot places the fixture back on the assembly line for quality control. 

At the end of the line, a VS 060 robot picks and places the finished sensors into trays for shipping to an automotive OEM.

The robots are fully integrated into the system via a Profibus network. All figures for the soldering process are being transmitted as integer variables, including soldering angle, soldering height, duration, speed and time. The robots were programmed in WinCaps using PacScript. 

Linked by an external VPN connection, the Ethernet-based control can be accessed by engineers on a touch screen control panel. Here, engineers can individually adjust all parameters of the soldering process, such as speed, path, duration and angle. This is a big advantage when assembly of different sensor models is required. It enables engineers to quickly and easily modify the soldering process without having to go through the time and effort of re-programming the base settings.

Quarder has been using Denso robots since 2013. The company chose the VS 6556G due to its six axes of motion, since the soldering process requires mobility and flexibility. The robot’s 7-kilogram payload capacity was important, since a fully loaded fixture weighs approximately 2 kilograms. The robot’s 0.49-second cycle time and its repeatability of ±0.02 millimeter were crucial, as well. 

Working in a three-shift operation, the system assembles 10,800 sensors every 24 hours. The error rate of the soldering process is just 1 percent.

For more information on robots, visit www.densorobotics.com. For more information on assembly automation, visit www.quarder.de. 

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