## 4. Accident Prevention System for Heavy Duty Machines--A Case Study of Small Demolition Robots
The tests revealed that when the machine is equipped with particular types of hammers it is not fully stable at the tilting angle of \(\alpha_{\text{C}}=0^{\circ}\), which indicates that in situations where the level of the ground is at a higher angle than \(0^{\circ}\), the robot can overturn towards the front. Such cases commonly result in accidents. For machines with a cabin, the function of protecting the operator is performed by the protective structure [1; 2; 28], while in the case of remote-controlled robots the operator must pay attention not to crush or hit the machine. The basis for the use of an HMI (Human-Machine Interface) is constant access to live-data recorded during (de-) construction works performed by the demolition robot [27; 31]. Measurements and several runs with a Commtest VB7 vibrometer were also performed during the tests to determine values for external loads acting on the robot arm. The data obtained from sensors in the experimental tests were used to estimate the worst cases when an accident can occur, which could be very significant  
Figure 8: Experimental testing of remote-controlled demolition robots in a real-life application: (a) working arm positioned at its furthest point in front; (b) demolition of a concrete structure. for accident prevention. To collect similar information about acceleration spectra in single, pre-defined measurement points while the robot was operating, a test run was also performed with the Phantom V12 high-speed camera at 2000 frames per second. The location of sensors and the high-speed camera measurements are shown in Figure 9. The results of experimental tests should be combined with the results of numerical simulations based on the discrete model of the demolition robot (CAE--computer-aided engineering) [28; 30]. The calculations performed with the application of the Finite Element Method could be a part of additional research [23], which could provide additional data about the machine condition and high stress cases that can lead to machine failure [23]. The results can be assessed by means of TEMA Motion, which shows the data collected in the first operation mode on waveforms for displacement, velocity. and acceleration in the aforementioned pre-defined measurement points on the demolition robot. The test run depicted above was performed for two different, but most common operating modes of the demolition robot: the first one is when the robot operates at optimal performance. The second mode of operation requires heavy duty hammering, but the hammer is not properly located inside the material that is being demolished. This represents a case when the positioning of the robot is suboptimal relative to the material that is being demolished or a case immediately after destroying the material when the tip of the hammer has to be repositioned. This operation can excite heavy vibrations in the machine [23; 29], which can also propagate in the material and cause the machine to slide down the excavation pit. To compare the aforementioned data for both modes of operation a visualization generated in National Instrument LabVIEW is combined with the readout from TEMA Motion. Figure 10 shows the time graph of acceleration for the pre-defined point on the hydraulic hammer (presented in Figure 9b) during proper and improper use of the tool. The spectrum analysis can provide information to the operator about the improper use of the robot. This can help to correct the arm positioning in order to increase the working efficiency as well as to decrease the risk of machine failure resulting from operation in unfavorable conditions. Figure 9: Experimental testing of a demolition robot with the use of: (**a**) vibration sensors positioned on the working arm of the robot depicted in Figure 8b, with an indication of measurement point T1; (**b**) high speed camera measurements (with an indication of the measurement point located on the hammer). Apart from accelerometers, the testing system was also equipped with classical strain gauges.