Trafficability Assessment of Deformable Terrain through Hybrid Wheel‐Leg Sinkage Detection

Abstract

Off-road ground mobile robots are widely used in diverse applications, both in terrestrial and planetary environments. They provide an efficient alternative, with lower risk and cost, to explore or to transport materials through hazardous or challenging terrain. However, nongeometric hazards that cannot be detected remotely pose a serious threat to the mobility of such robots. A prominent example of the negative effects these hazards can have is found on planetary rover exploration missions. They can cause a serious degradation of mission performance at best and complete immobilization and mission failure at worst. To tackle this issue, the work presented in this paper investigates the novel application of an existing enhanced-mobility locomotion concept, a hybrid wheel-leg equipped by a lightweight micro-rover, for in situ characterization of deformable terrain and online detection of nongeometric hazards. This is achieved by combining an improved vision-based approach and a new ranging-based approach to wheel-leg sinkage detection. In addition, the paper proposes an empirical model, and a parametric generalization, to predict terrain trafficability based on wheel-leg sinkage and a well-established semiempirical terramechanics model. The robustness and accuracy of the sinkage detection methods implemented are tested in a variety of conditions, both in the laboratory and in the field, using a single wheel-leg test bed. The sinkage-trafficability model is developed based on experimental data using this test bed and then validated onboard a fully mobile robot through experimentation on a range of dry frictional soils that covers a wide spectrum of macroscopic physical characteristics

Models for Slip Estimation and Soft Terrain Characterization With Multilegged Wheel–Legs

“…(27). Moreover, the sinkage of each wheel-leg was estimated using the output of the IR according to the method presented in [15] in order to estimate the same soil characteristics using Eq. (29).…”

“…In addition, wheel-leg sinkage estimates obtained using the methods presented in [15] can provide additional information towards the physical characterization of different soils. Similarly to [32] and [33], the models applied are kept linear to favor efficiency for online computation.…”

“…The Robot Operating System (ROS) middleware framework is used for computational load distribution and flexibility of integration with different robot platforms. The details of the hardware and software implementation of the system introduced in this section are described in [15].…”

“…Tests on both platforms were carried out with five distinct levels of commanded slip: no slip (0%), 12.5%, 25%, 37.5% and 50%. More details on the experimental setups and their operation can be found in [15].…”

“…Figure 4 illustrates this with simulation screenshots, including section labels and interface stresses, using the wheel-leg shown in Fig. 1, equipped with: (a) The Load Testing Foot (LTF) [15], which consists of a prominent convex front 'tip' and a non-existent 'heel'. (b) The Symmetric Rubber Foot (SRF) [21], which counts with flat 'heel' and 'tip' sections of equal dimensions.…”