High Precision Sensor Technology in Robotics Applications

For years now, the Robot technology has been showing enormous growth and its market has been flourishing and thriving. Many modern industries worldwide are now relying more on high precision robots that operate at 100% reliability and intelligence. By using this technology, the operators enjoy the benefit of increased flexibility in the process of production, higher quality and reduction of cost in materials that allow them to save more. When smart robot technology is discussed, importance is given to the innovative sensors that act as interface between the robot and its environment.

There is an increasing demand for intelligent robotics. Some of its fundamental requirements are durability, higher and flexibility, lower costs and total accuracy down to the micron range.  Modern sensors play a major part in the fulfillment of these requirements.

Some of the examples are: camera systems perceiving the environment, temperature sensors detecting hot spots and bodies and laser triangulation sensors determining micrometer-precise distances and positions. The robot needs information about the position of tools and the production goods for it to be able to carry out its task. It is particularly important that there is a reliable operation with collaborative robots involving interactions with human machines.

Two different possibilities are distinguished when it comes with robotic applications sensors. One is the internal sensors that ensure the robot’s correct operation. The status data of the robot must be determined, such as its room orientation, calibration, speed measurement or recognition of rotating movements.  

One example of this application is the robot axes calibration carried out by induSENSOR LVDT displacement sensors from Micro-Epsilon. These robot axes must be adjusted at regular intervals during commissioning within the context of quality assurance. Using a feeler gauge, the measuring gauges are mounted on the axes of the robot and identify the zero point while the axis is being rotated. The feeler gauge is evaluated by the integrated electronics and transmits a switch signal to the robot control.  

Through this procedure, the robot is reliably adjusted, independent of the operator. While being measured at high speed and automatically being fed into the control system, downtime is also avoided. The compact size of the gauges makes it perfectly suitable. It enables their integration into very small installation spaces. They also provide high speed and high repeatability switch signals.

Their robust housing guarantees an extended service life. In partnership with a worldwide leading supplier of robotics, Micro-Epsilon has developed the induSENSOR for robot axis calibration.

Robot axes must be calibrated at regular intervals. Micro-Epsilon’s induSENSOR (LVDT) displacement sensors carry out this task. Mounted on robot axes, these gauges detect the zero point via a probe tip when the axis is turning.

Robot axes must be calibrated at regular intervals. Micro-Epsilon’s induSENSOR (LVDT) displacement sensors carry out this task. Mounted on robot axes, these gauges detect the zero point via a probe tip when the axis is turning.

On the other hand, there are external sensors that supplies data and measurement values about the robot’s environment. They identify the position of the work piece within the room, but also allow tactile perceptions. The following are the critical factors considered on the sensor technology that will be used: enormously high precision and speed, direct communication, stability, full integrity, real-time measurements that are real time, endurance and wear-free dependability.  Optical sensors from Micro-Epsilon carry out these demands. Laser point and laser line sensors of the optoNCDT and scanCONTROL series are utilized.

Absolute Precision in Automotive Production

The sector where most industrial robots are used is the automotive industry. With that, the requirements concerning cycle time, automation degree and repeatability are rising. In the production and processes of joining from the shock absorber to the front spoiler and the lights, a lot of steps need to be carried out during which different parts are joined. In the past, the production processes were stiff but now, these processes are already controlled in real-time through the use of state-of-the-art sensor technologies.

Meanwhile, the tolerances of the gap sizes have been cut into half and are now between 0.5 mm to 2 mm. For these tolerances to be achieved, all the working steps must be correctly carried out. For example, the joining processes in production automation require precise assembly. This is the reason why robots are now used instead of these processes.

In addition to the optical-visual impression, it must be ensured that the correct and long-life functions are all being used. For example, squeaking doors are not okay, windows must always be tight and flush must be installed. Similarly, ideal appearance and functionality of the vehicle must be achieved using lesser material as possible. For these kinds of tasks, robots are very much suitable because they work endlessly and consistently, and operate fast and accurately without psychological and physiological impairments.

Moreover, they also do many tasks that formerly would have needed heavy manual labor for employees. Laser sensors and laser scanners from Micro-Epsilon are utilized in these applications for intelligent robotics. They detect measurement values in real time and can directly transmit these to the PLC. Among the results are improvement on quality control based on extremely high accuracy, optimization of the processes, and savings in cost and materials.

Marriage of Engine and Car Body

OptoNCDT laser point sensors, to sight one example, monitor the "marriage" of the car body and the engine. Car body and engine, such as the entire drive train, are joined together through the so-called marriage lines.

For that reason, the drive train is moved into the production line on a frame. The car body is then suspended from a device and is swiveled from above by a robot in such a way that the car body is above the drive train, which is then lowered onto it. The distance between the engine and the car body are then measured by the laser triangulation sensors mounted on the device. Finally, the car body must be positioned precisely onto the drive train and must be secured accordingly.

Vehicle positioning: Micro-Epsilon’s laser scanners accurately position the vehicle.

Vehicle positioning: Micro-Epsilon’s laser scanners accurately position the vehicle.

High Precision Cockpit Positioning

The cockpit in the car is made up of hundreds of individual parts and weighs up to 100kg. It must be placed accurately during its installation into the vehicle. On the outsides of a robot arm, a rectangular frame of metal struts with two grippers is placed. The gripper then grips the cockpit on both sides and horizontally moves it in the direction of the vehicle, which is placed into the assembly line on a conveyor belt.  Before reaching the vehicle, the robot slants the cockpit side so that it would be mounted slightly downwards. In this placement, the cockpit is swiveled into the passenger compartment over the robot through the opening, which is intended for the driver door and then turned horizontally again.

Four optoNCDT laser sensors are typically used for these measurement tasks. These are installed in the four corners of the metal frame respectively. They are placed in the four corners of the metal frame, both on the top and the bottom, which is equipped with the grippers. The sensors determine reference points in the vehicle interior in real time. These can either be prominences or depressions.

The four sensors are the ones that ensure that the cockpit is aligned accurately in all directions (x-, y- and z-axes). When all sensors have identified their respective reference marks, the robot is put to a stop so that the cockpit can be moved forward into the exact position relative to the car body, to dock it on and to fix it in place.

The entire process, including the fitting of the cockpit, only requires less than one minute, an extremely short cycle time. The sensors, however, must operate separately of the surfaces, because different reflections occur caused by the multitude of surface paints used – from dark to bright colors and from mat to shiny appearances.

Strengths of the Laser Point Sensors

One of the best among its class, optoNCDT laser point sensors are used for measurement of thickness, displacement and distance. The Real-Time Surface Compensation feature (RTSC) allows the sensors to operate without regards to the materials and colors. The measurement of very small objects is also enabled through the use of extremely small measurement spot size, while at the same time providing high accuracy measurements down to the micrometer range.

Considered one of the best in their class, these laser point sensors are used in displacement, distance and thickness measurements. Due to the RTSC real-time surface compensation feature, the laser-optical measuring system operates almost regardless of material and color.

Considered one of the best in their class, these laser point sensors are used in displacement, distance and thickness measurements. Due to the RTSC real-time surface compensation feature, the laser-optical measuring system operates almost regardless of material and color.

Measurement data is commonly accessible in real time. It can be used to correct and control the production process automatically. Depending on the model, Micro-Epsilon’s wide product range of red and blue laser scanners covers measuring ranges from 2 mm to 1000 mm and measuring rates from 2 kHz to 49.14 kHz with resolutions down to 0.03 μm. High precision laser sensors from Micro-Epsilon are often used in high-tech areas such as automotive industry and 3D printing, where aircraft components are also produced.

Car Windows

In the automotive industry, measurement tasks where the simultaneous detection of multiple measurement values and three-dimensional detection of measurement objects within short cycle times are required. For example, during a windshield installation, a scanCONTROL laser line sensor identifies detailed distance values in all axes.

In the process of installation, the sensor is mounted onto the robot that fits the window into the vehicle. When the windshield is positioned in the car, the scanner detects the complete profile and vicinity of the windshield while it determines all necessary values with a single run in quick time. It can be decided whether the windshield is placed right, whether it is placed straight and centered or whether it fits flawlessly in every plane. The results, the gap and flushness in this case, are directly generated in the sensor head and output to the PLC.

Adhesive beading: In the automotive industry, there are measurement tasks which require simultaneous detection of several measurement values or three-dimensional detection of measurement objects within short cycle times. For example, when assembling the windshield, a scanCONTROL laser line sensor is used to detect detailed distance values.

Adhesive beading: In the automotive industry, there are measurement tasks which require simultaneous detection of several measurement values or three-dimensional detection of measurement objects within short cycle times. For example, when assembling the windshield, a scanCONTROL laser line sensor is used to detect detailed distance values.

Adhesive is another measurement task concern, which is already applied before the windshield is fitted into the chassis and also detected by a laser scanner. As a result, the scanner is directly mounted onto the robot that applies the adhesive beading. Here, the sensor moves along the adhesive bead to create a 3D image. It reveals whether there is a sufficient quantity of adhesive, whether it is evenly applied and whether the bead is correctly applied in the right places. All measurement values that are detected are separately stored. These can be used for analysis purposes if an error occurs in the process at a later point in time.

Gap Inspection

A number of flushness and gap measurements are necessary when a vehicle is being assembled. This includes the inspection of the airbag stitching position. The scanner identifies the contour of the stitching while it is being guided by a robot arm and assesses several features synchronously. The distance between the stitching and the separating point between the single stitches is continuously inspected by the laser scanner and it outputs the evaluation directly as 0 (NOK) or 1 (OK) via the Ethernet interface. Further than that, the difference in height between two single components is directly checked in order so that any faulty assemblies that might impair the safety will be detected immediately.

Gap inspection: Important parameters of quality are homogeneous gap sizes of cockpit elements and the center console. Depending on the inspection scenario, a single scanner applied on a robot arm can measure different gaps in static or dynamic mode.

Gap inspection: Important parameters of quality are homogeneous gap sizes of cockpit elements and the center console. Depending on the inspection scenario, a single scanner applied on a robot arm can measure different gaps in static or dynamic mode.

Another measurement task involves gap monitoring in car interiors. Essential considerations of quality are gap sizes of cockpit elements that are homogenous and the center console. Depending on the situation of the inspection, a single scanner applied on a robot arm can assess different gaps in a static or dynamic mode; otherwise, a special frame on the robot arm is utilized. This will enable the scanner to detect a number of different gaps in the interior in static mode within fractions of a second.

The sensor then assesses these measurement values and sends a signal to the control system if the values measured fits the tolerances defined by the customer. Other gap inspections also concern the car body, an example of this is measuring gaps in doors or when assembling body trims.

Strengths of Laser Line Triangulation

A strength of scanCONTROL laser scanners that permits its integration in restricted installation spaces is its compact design. The entire electronics is placed in the sensor head. This makes the installation of the sensor on the robot easier.

Robot-suitable cabling allows extreme twists and torsion movements on the robot arm. Added to that, the laser scanners are set with an integrated, highly receptive receiving matrix that allows measurements on almost all industrial materials, mostly independent of the surface reflection.

The laser scanner can quantify large measuring ranges in a single operation. One relative movement between sensor and measurement objects permits the scanner to fully identify even three-dimensional profiles or images of surfaces down to the micrometer range. Real-time quality control allows immediate production control intervention. Micro-Epsilon offers laser scanners with either red or blue laser diode. This is usually only used when the red laser light is operating at its limits, such as with semi-transparent, wood or organic materials or red-hot glowing metals.

The blue laser light can be more sharply focused on certain surfaces where it provides high precision measurement results. The laser scanner set up and configuration is done through the Configuration Tools PC software, which can be used, for example, to measure steps, grooves and angles.  The sensor keeps a record of the parameter sets. Outputting OK/NOK signals and directly feeding the measured values into the PLC are all very doable.

If the user wants to externally evaluate the profile data, the laser profile scanner can also produce all raw profiles of the sensor matrix. An Ethernet interface with GigE Vision makes a PC connection possible. In order to make the integration into a customer’s own software simpler, Micro-Epsilon offers libraries for C, C++ and C#, as well as LabVIEW drivers. Integration into Linux environments is also not a problem because of the corresponding libraries.

Micro- Epsilon also offers special accessories to protect the scanner for applications in harsh environments. To cite an example, a special housing with windows that are exchangeable is available for welding applications. A special compressed-air purge system makes the optical components dust-proof. For use in high ambient temperatures, the laser scanner can be inserted into a cooling jacket.

scanCONTROL: Laser scanners from Micro-Epsilon enable measurements on almost all industrial materials, largely independent of the surface reflection.

scanCONTROL: Laser scanners from Micro-Epsilon enable measurements on almost all industrial materials, largely independent of the surface reflection.

In addition to the sensor technology, the customer’s application is also an important factor when choosing the appropriate sensor. Micro-Epsilon offers specialist advice and industry expertise based on 50 years of technology experience. From the start of the discussions up until the installation of the sensors, the customer is always backed up by a strong partner when solving individual measurement tasks. Micro-Epsilon focuses on the development of customer-specific solutions while offering a wide range of modern products that also allow the standard sensors to be adapted to customer-specific requirements.

This information has been sourced, reviewed and adapted from materials provided by Micro Epsilon.

For more information on this source, please visit Micro Epsilon.

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