Table 1 Applications and quality of sensors
From: Robotic arc welding sensors and programming in industrial applications
Operation time | Type of sensors | Advantages | Drawbacks |
|---|---|---|---|
Sensing independent | Touch sensing | Can recognize 3-dimensional offset of the workpiece. The wire tip or the gas nozzle can serve as a sensor. Can be used for accurate learning of the path before welding. | Can defect elastically, using tactile probes it is difficult, if not impossible, to provide information on the joint fit up. Poor weld joint repeatability. |
Preview sensing | Contact sensing | Relatively low cost. The mechanically probes leads the welding spots. | Not adaptable to suit a variety of joint geometries. |
Inductive sensing | Largely used in industry, configurations with one pick-up coil can provide a cross-seam or vertical path correction signal. | Different sensor is needed for each type of joint, should stay very close to the joint | |
Capacitive sensing | Offer the opportunity to measure the distance between the workpiece and an electrically conduction plate of small dimension. | It is hard to extract a correction signal in two direction from the capacity variations | |
Acoustical sensing | Apart from seam-tracking application, an acoustical sensing system can be used to explore the workpiece for obstacle and maybe to inspect a produced weld. | Line of sight must not deviate from the surface normal; another limitation is the temperature dependence of the speed of the sound. | |
Optical sensing | Can be used for seam tracking as well as for geometrical recognition of the weld pool, to adapt process parameters in the case of possible deviations. | To prevent accessibility limitation, it may require additional axes for seam tracking, tremendous effort to introduce technical integration, regularly check the lens protection. | |
On-the-spot sensing | Weld pool observation | Dedicated to welding pool geometry and properties. The obtained image is processed and pattern recognition algorithms are used to extract the dimensions and form of the weld pool. Different sensors can be applied: optic sensing, thermal sensing, real-time radiography, weld pool oscillation sensing, | There should be a clear interpretation of the image by the system, in order to give torch corrective changes accordingly |
Through-the-arc sensing | No additional voluminous sensor needs to be fixed to the weld torch. Its simple operation and implementation have made arc sensing a commonly accepted off-the-shelf technique. | The torch has to be weaved during welding. The dimension of the joint must exceed some critical dimension, e.g., it is not applicable for sheet metal. In addition, a signal can be obtained only after the arc has been established. Therefore, it cannot be used for finding starting point of the weld. |