Hamza Khan

Longitudinal and lateral slip control of autonomous wheeled mobile robot for trajectory tracking

This research formulates a path-following control problem subjected to wheel slippage and skid and solves it using a logic-based control scheme for a wheeled mobile robot (WMR). The novelty of the proposed scheme lies in its methodology that considers both longitudinal and lateral slip components. Based on the derived slip model, the controller for longitudinal motion slip has been synthesized. Various control parameters have been studied to investigate their effects on the performance of the controller resulting in selection of their optimum values. The designed controller for lateral slip or skid is based on the proposed side friction model and skid check condition. Considering a car-like WMR, simulation results demonstrate the effectiveness of the proposed control scheme. The robot successfully followed the desired circular trajectory in the presence of wheel slippage and skid. This research finds its potential in various applications involving WMR navigation and control.

Bio-inspired knee joint mechanism for a hydraulic quadruped robot

Over the last few decades, legged robots are becoming a promising solution for rough terrain navigation, however, existing legged machines often lack versatility to perform a wide range of different gaits. To build a highly dynamic and versatile legged robot, it is essential to have lightweight legs with optimized design and suitable actuators for the desired robot performance and tasks. The design goals are to achieve (1) a wide range of motion for bigger foot workspace which will increase rough terrain walking performance by increasing the number of reachable footholds for each step, (2) optimized joint torque curve since torque output is related to joint angle if linear actuators like pistons are used. In this paper, we focus on the knee joint and propose the adaptation and optimization of the so-called isogram mechanism. It exhibits a changeable instantaneous center of rotation (CICR), similar to a human knee joint. We will show how an optimization of design parameters lead to a knee joint design that satisfies the above-mentioned goals. The main contributions of this paper are the kinematic and torque analysis of the isogram mechanism that is actuated by a linear actuator; the optimization of the mechanisms design parameters; a comparison between the proposed knee joint with the hinge-type knee joint of the quadruped robot HyQ; and experimental results of a proof-of-concept prototype leg featuring the proposed mechanism.

DESIGN AND SCALING OF VERSATILE QUADRUPED ROBOTS

The rough terrain mobility of legged robots is expected to exceed the performance of their wheeled or tracked counterparts. To fully take advantage of the legs, such robots need to be versatile by achieving highly dynamic motions at the same time as careful navigation over rough terrain. Highly dynamic robots need to be designed to be fast and strong enough to run and jump. A dynamic robot needs to be light and powerful at the same time. Two requirements that are conflicting and therefore have to be traded off. In this work we present a tool that helps quadruped robot designer to better select and size joint actuators for various robot sizes. We use the squat jump as characteristic motion of a highly dynamic robot and estimate required joint torque and velocity in relation to maximum jump height, body mass and leg segment length.

ACTUATOR SIZING FOR HIGHLY-DYNAMIC QUADRUPED ROBOTS BASED ON SQUAT JUMPS AND RUNNING TROTS

It is challenging to design a quadruped robot that can perform highly dynamic tasks like jumping and running. Estimating appropriate range of joint torques and velocities is essential for the selection of the leg actuators. Jumping and running are considered as extreme tasks that push the actuators to their limits. In this paper we proposed a simple method that allows a quadruped robot designer to obtain approximate peak joint torques and joint velocities needed for a running trot at various forward velocities and squat jumps at different heights. A SLIP model is used for the mapping of CoM trajectory of a quadruped robot during a running tort. Experiments for a squat jump and running trot are performed with the highly dynamic quadruped robot HyQ for the validation of the proposed approaches. A case study is also discussed to demonstrate the usage of proposed tool.

Towards Scalable Strain Gauge-Based Joint Torque Sensors

During recent decades, strain gauge-based joint torque sensors have been commonly used to provide high-fidelity torque measurements in robotics. Although measurement of joint torque/force is often required in engineering research and development, the gluing and wiring of strain gauges used as torque sensors pose difficulties during integration within the restricted space available in small joints. The problem is compounded by the need for a scalable geometric design to measure joint torque. In this communication, we describe a novel design of a strain gauge-based mono-axial torque sensor referred to as square-cut torque sensor (SCTS), the significant features of which are high degree of linearity, symmetry, and high scalability in terms of both size and measuring range. Most importantly, SCTS provides easy access for gluing and wiring of the strain gauges on sensor surface despite the limited available space. We demonstrated that the SCTS was better in terms of symmetry (clockwise and counterclockwise rotation) and more linear. These capabilities have been shown through finite element modeling (ANSYS) confirmed by observed data obtained by load testing experiments. The high performance of SCTS was confirmed by studies involving changes in size, material and/or wings width and thickness. Finally, we demonstrated that the SCTS can be successfully implementation inside the hip joints of miniaturized hydraulically actuated quadruped robot-MiniHyQ. This communication is based on work presented at the 18th International Conference on Climbing and Walking Robots (CLAWAR).

Robotized task time scheduling and optimization based on Genetic Algorithms for non redundant industrial manipulators

Industrial robot manipulators must work as fast as possible in order to increase the productivity. This goal could be achieved by increasing robots speed or/and optimizing the trajectories followed by robots while performing assembly, welding or similar tasks. In our contribution, we focus on the second aspect and we target the shortening of paths between task-points. In other words, the goal is to find the shorter traveled distance between different configurations in the coordinate space. In addition to the short distance goal, we aim as well to impose both IKM (Inverse Kinematic Model) and the relative position and orientation of the manipulator regarding the task-points. To this end, we propose an optimization method based on Genetics Algorithms. The method is validated via numerical and graphical simulation, where, results show that the total cycle time required to perform a spot-welding task of an industrial car-body by a 6-DOFs (Degree Of Freedoms) industrial manipulator was drastically reduced.

AN INNOVATIVE TORQUE SENSOR DESIGN FOR THE LIGHTEST HYDRAULIC QUADRUPED ROBOT

High-performance legged robots that are required to navigate on unstructured and challenging terrain benefit from torque-controlled joints. High-fidelity torque measurements are crucial for proper joint torque control. Commercially available torque sensors are expensive and often hard to integrate into compact and light-weight robot leg designs. Custom-made sensors on the other hand often suffer from asymmetric behaviour with respect to direction of rotation or poor linearity, especially for small and compact applications. This work is motivated by the need to achieve reliable torque measurements for the newly developed, small-size hydraulically actuated quadruped robot MiniHyQ. The main contribution of this work is the development of a new innovative design of a strain gauge based torque sensor with a high degree of linearity, symmetry, and scalability (both in dimension and measuring range). Furthermore, the glueing and wiring of the strain gauges are easy thanks to the geometry of the sensor that allows direct access to the mounting surfaces, even in compact dimensions. We show the design’s symmetric (clockwise and counterclockwise rotation) and linear behaviour through virtual prototyping and experimental tests. Furthermore, we show how a small-scale instance of the sensor design is successfully installed on the MiniHyQ robot.