Figure 5 shows an example of a visual weld inspection system (VIROwsi from Vitronic GmbH) consisting of a camera-based sensor, computing unit, and software having

the capability of  fully  automated  three-dimensional seam inspection with combined 2D and 3D machine vision。 It can detect all the relevant defects and their position in real time。 These informations can be stored for later follow-up, documentation, and statistical evaluation  (VITRONIC 2010)。

Figure 6 shows an example of a weld inspection sen- sor based on a scanning thermal profile called ThermoProfilScanner (TPS), from HKS Prozesstechnik GmbH, for evaluation of weld quality and misalign- ment of welds during cooling。 As the characteristics of the thermal profile (symmetry, width of a thermal zone, maximum temperature, etc。) and the seam quality are directly correlated, seam abnormalities like insufficient weld penetration, weld seam offset, holes, lack of fusion, etc。 can be detected by TPS。 Correlations between thermal profile and weld quality from previous experience can be used to compare the desired values and tolerances。 When tolerance limits are exceeded, warning signals are pro- duced marking the defective points and the weld process can be stopped (HKS Prozesstechnik 2013)。

Seam-tracking and seam-finding  sensors

Several sensors for robotic welding, mainly for seam tracking and quality control, are commercially available。 Some of the more renowned sensor products in the field of robotic welding are discussed below:

Robo-Find (Servo Robot  Inc)

The sensor in the Robo-Find system for seam finding in robotic welding is based on a laser vision system。 Robo- Find provides a solution for offline seam-finding applica- tions where parts and/or features must first be located when modifying the tool path。 It locates, detects, and mea- sures weld joints without any contact with the part  and then signals the robot to adjust torch trajectory in less than 1 s。 Some of the features and benefits of Robo-Find (Servo Robot Inc) are listed below (Servo Robot Inc 2013a):

●It is immune to arc process like spatter and can withstand radiated heat。

●It can find seams for all weldable materials。

●It has an embedded color video camera for remote monitoring and programming。

●It has the ability to recognize joint type automatically。

●It reduces repair and rework。

●It can be retrofitted to existing  equipment。

●It employs smart camera technology with embedded control unit (no separate controller with everything inside the camera itself ) such that setup can  be

done with a simple laptop interface。

Robo-Find is available with one of two types of laser camera, based either on a point  laser  sensor  or  on  a line laser sensor system。 Figure 7 shows the Robo-Find SF/D-HE system, which is based on a line laser system, and the SENSE-I/D-V system, based  on  a  point  laser。 An approximate comparison of the time requirement between the laser-based vision sensor and a mechanical tactile sensor for seam finding and welding is shown in Fig。 8。

Power-Trac (Servo Robot Inc) This sensor has the capability of real-time seam tracking and offline seam finding based on a laser vision system。 The trajectory of the torch is modified continuously to compensate for real-time  changes  such as warping caused  by  heat input

during the welding process。 Some of the features and benefits as mentioned by the manufacturer are as  fol- lows (Pires et al。 2006):

1。It is a fully integrated system complete with laser camera, control unit, and software。

2。It offers automatic joint tracking and real-time trajectory control of the welding  torch。

3。There is an option for an inspection module for quality control of the welds。