# An Overview of Industrial Robots Control and Programming Approaches
## 4 Innovative Control Approaches
### External Trajectory Generator
The first is adopted to move the robot along a path consisting of position data generated externally and streamed every 4 ms (with a control lag of up to 20 ms), whereas the latter allows for real-time path corrections using sensor data. In this case, corrections must be provided in the robot's coordinate system every 48 ms. The double operation  
Figure 4: Closed-loop real-time position- and force-based guided motions. On the left, an example of precise robot positioning with laser tracker feedback; on the right, an application of hand-guiding on a high payload IR. mode is also proposed by Fanuc with the modal DPM and the inline DPM. The first is intended for applications that require continuous modification along the designed path, with a cycle rate of 8 ms and a reduced control lag. As for the inline DPM, each motion segment is adjusted only at its final destination with an offset value. From a comparison, the RSI potentially outperforms the other solutions by allowing dynamic compensations up to 250 Hz. However, the bandwidth of the established closed-loop system varies on a case-by-case basis, and more practical evaluations should also consider communication delays and control lags. The described packages have been widely employed by many academic researchers. A summary of their contributions is reported in Table 3. A first example of an RSI application, already cited in Section 4.1, is the KCT toolbox. In this case, the trajectory generated via MATLAB is streamed to the robot without implementing any real-time feedback (i.e., sensor signal). An extended version, named RoBO-2L, is introduced in [38] to deal with older generation robot controllers. The implementation of an external sensor can be seen, for example, in [39], where a vision system is attached to the robot's end-effector to allow the robot to perform tasks without a predefined program. After a series of tests, the authors concluded that it is possible to use RSI not only for minor path corrections but also for manipulating objects in an adaptive way. Another application, still based on the use of a vision system (C-Track 780 from Creaform), is described in [40], where the authors successfully demonstrated their dynamic pose correction systems by reaching an IR pose accuracy of 0.050 mm. As for the online path compensation during robot traveling (see the left schematic of Figure 4), effective solutions implemented on KUKA, ABB, and MABI robots can be found, respectively, in [41; 42], in [43] and in [44], where positioning errors are reduced by about 90%. These results become particularly important for extending the use of IRs to large-scale machining operations. To this aim, promising results have also been obtained by means of force-based compensations, as documented in [45; 46; 47]. In general, the adoption of force/torque sensors directly mounted on the robot's end-effector has been extended to many fields, ranging from automatic part handling to the execution of collaborative tasks (e.g., operator hand-guiding as depicted in Figure 4 and described in [48; 49]). These examples prove the advantage of controlling the robot considering specific (i.e., application-dependent) needs. In fact, the use of sensors capable of guiding or protecting the robot during movement allows IRs to replace exclusive machines normally used in production lines. However, it should once again be recalled that the user becomes responsible for manipulating parameters such as velocity, acceleration, and position, as well as defining the interpolation strategies. If any detail goes unnoticed, mechanical damages may not only make further IR use unfeasible but may also pose serious risks to users [50]. Problems such as vibrations during robot motion were observed in experiments performed with non-optimized codes. Other crucial points are the limited set of functions and I/O and a major (unavoidable) economical investment for packages purchase.