CASE STUDY

Vision system and Cartesian robot reduce parts failure in automotive plant

TMR156TM Robotics in conjunction with its Spanish key integrator Masser Robotica SA has provided Dinalot, a Spanish manufacturer of automotive parts, with a Cartesian robot cell to improve production. The robot has reduced component rejection on a high-speed line that manufactures metal disks for use in vehicle fuel injection systems.

The Cartesian robot works in conjunction with a machine vision system in a quality assurance role. There are five versions of the metal disks, which incorporate six tapped and countersunk holes. Before the process was automated, an operator checked the diameters of the holes and their positions relative to a central notch.

This time consuming process involved selective sampling and, as a result, allowed some non-compliant parts to pass through. “Any process where only a portion of a batch is checked inevitably produces errors,” explained Nigel Smith of TM Robotics. “By checking component parts with an automated vision system, the user can drastically reduce such errors.”

The new system uses two vision sensors mounted on the robot arm and a rack mounted PC. The computer controls the sensors and robot, and displays the inspection images and measurement results.

Another monitoring and control option, not used in this application, would have been the TS1000 controller. It features a built-in PLC that makes it easy for the robot to interface with peripheral devices, rendering the robotic cell a tool for complete system control. The controller features a built in PLC to simplify and increase the speed of data transfer.  Designated the Tcmini, the PLC can control external I/Os (21 inputs and 17 outputs) and I/Os (five inputs and four outputs) and panel I/Os (two inputs and two outputs). Data transfer between the robot and PLC is performed through the robot controller interface relay. Additional I/O extension is offered as an option via serial communication. An I/O module (64 inputs and 64 outputs) can be connected using the RS-485 port at up to 400m away, by using just one cable. The range of control options further increase the versatility of the Cartesian robot range.

In the Dinalot application, the parts arrive at the inspection station after passing through a cleaning bath. Each part is picked up by the robot arm and placed on a surface backlit by LEDs. The first vision sensor locates the positioning notch and the arm moves it to the correct point above the part. The sensor then calculates the position of each hole relative to the notch (to an accuracy of ±0.01 degrees), and measures their diameters (to an accuracy of ±0.02mm).

The second sensor inspects the inside of each hole to check the number of threads and measure the width of the grooves. Parts that pass these tests are placed on a stacking device, while failed parts are sent to a discard container. The Cartesian robot also palletises the inspected parts, further improving productivity.

Smith believes that the Cartesian robot’s simplicity is its strength, “No matter how expert engineers may be in their own machines and processes, few are motion specialists.” He continues, “To develop even relatively simple motion and manipulation systems requires hundreds of man-years of experience.  Yet attempts to package such motion systems have usually resulted in compromise that undermines machine functionality or requires levels of integration expertise that exceed those available.

“The idea behind the system is to enable engineers to take linear axes, bolt them together in hundreds of different configurations, and create complicated work handling and process robots easily. I see this as a breakthrough for machine builders. The modular system provides a relatively small number of basic components. These are guaranteed to be compatible with each other and can be configured to create over 500 variations. The system consists of a variety of linear axes, which are coupled with controllers that contain both the AC servo motor amplifiers and the motion control hardware.  A teach pendant and programming software complete the package. The Meccano construction kit analogy, though often over-used by engineers, genuinely applies in this case,” Smith concludes.

One of the advantages for the design engineer is the fact that all the axes are identical and can be used in any plane.  Potential applications for the Cartesian robot include feeding, testing, cutting, soldering, screw fastening, riveting, positioning, loading and unloading, vision systems, sealing or gluing and pick and place. As well as Dinalot, other applications that have already used such robots include a host of production lines, from PCB manufacturers to companies producing huge volumes of nuts and bolts.

The entire operation at Dinalot now takes just nine seconds, allowing every part produced to be inspected. The data generated by this system has allowed Dinalot to refine other areas of its machining processes, resulting in long-term benefits as well as short-term payback