In this work, we present an approach for realizing the torque control for a parallel-actuated robotic system by mapping the motion of a linear series elastic actuator (LSEA) to its driven robot joint. In most standard robotic modeling and control strategies, a robot is assumed to be actuated by torques applied directly at each joint and constructed as an open kinematic chain. However, the use of non-direct-drive actuators can violate these assumptions, causing additional challenges for the modelling and control of the robot. On our humanoid robot we use standard high level controllers to command desired joint positions and torques in order to generate desired behaviors. However, the humanoid robot is actually actuated by LSEAs, which are defined by actuator length and force. Overcoming this difference requires a method of mapping the motion and effort of an LSEA onto the corresponding joint of a robot. Our mapping approach allows for the conversion of generic desired joint position and torque trajectories consistent with standard controllers into actuator length and force trajectories that can be implemented on an LSEA-actuated robot. We present a two-stage methodology to achieve low-level torque control on our humanoid robot: a validation of the force-torque mapping in simulation, and a force controller implementation for tracking these resulting torque trajectories on a sample simulation of a single robot joint.
The main contribution of this paper is the design and development of the lower body of PANDORA (3D-Printed Autonomous humaNoid Developed for Open-source Research Applications), a new humanoid robotic platform implementing additive manufacturing techniques. The three joint configurations (hip, knee, and ankle) along with the major three structural parts (pelvis, thigh, and shin) of the lower body are discussed. The use of 3D printing and PLA+ material makes the robot an affordable solution for humanoid robotics research that gives a high power-to-weight ratio by significantly reducing the number of parts, as well as manufacturing and assembly time. The range of motion of the lower body of PANDORA has been investigated and is found to be comparable to a human lower body. Further, finite element analysis has been performed on the major parts of the lower body of PANDORA to check the structural integrity and to avoid catastrophic failures in the robot. The use of in-house developed actuators and robot electronics reduces the overall cost of the robot and makes PANDORA easily accessible to the research communities working in the field of humanoids. Overall, PANDORA has the potential for becoming popular between researchers and designers for investigating applications in the field of humanoid robotics, healthcare, and manufacturing, just to mention a few. The mechanical designs presented in this work are available open source to lower the knowledge barrier in developing and conducting research on bipedal robots.
Investigating how bats manage to control their complex flight apparatus using streams of biosonar echoes as inputs with an approach based on biomimetic robotics, we have designed a bioinspired flapping robot that replicates some of the features of the flight apparatus of bats: In particular, it incorporates a mechanism to translate one degree of freedom from a motor into flapping as well as folding of the wings. Throughout the flapping cycle, the wings are folding and unfolding continuously in a way that achieves maximum upward lift. Similarly to a bat, a wing membrane is stretched over the wings and pulled taut. The design is primarily 3-D printed to reduce weight and allow for rapid prototyping. Future iterations of the robot will continue to reduce the weight and add more degrees of freedom to enable greater maneuverability in the air. After flight has been achieved, acoustics in the form of ultrasonic microphones will be implemented on the robot for further navigational capabilities. It is important to optimize the robot for the maximum amount of lift while keeping the robot as light as possible to allow for a greater capacity for acoustics equipment while still maintaining the ability to fly.
Effectively characterizing the significance of bioinspired design for the advancement of robotics technology is a complex endeavor. Here, a direct comparative analysis was conducted to examine the differences between a bioinspired bat robot and bats. The unique maneuvering and biosonar capabilities of bats have long been recognized as a source of technical inspiration. However, the capabilities of bats in these areas still far exceed those of current robotics models. To evaluate these differences, we have been preparing to fly rhinolophid/hipposiderid bats and a bat-robot prototype through a flight tunnel instrumented with arrays of 50 high-speed cameras and 32 ultrasonic microphones. Using this approach, kinematic and acoustic data can be compiled to enable a thorough comparison of the bats and the robot. This data can support a quantitative analysis of key characteristics such as wing cycle, size ratios, lift and thrust capacity, as well as maximum carrying capacity. Based on insight from this data, strategic design iterations can be carried out to more accurately mimic bat flight with considerations for incorporation of biosonar-inpsired technology into the design. By continuing this process, an in-depth understanding of the bioinspired design approach, implementation, and impact to the design process can be achieved.
To investigate the active sensing strategies used by echolocating bats of the genera Rhinolophus and Hipposideros, we have constructed a 9-meter long flight tunnel, which incorporates an array of 32 ultrasonic microphones distributed throughout the tunnel. Rhinolophus and Hipposideros are of special interest because of their highly flexible biosonar system; these bats emit pulses from their nasal cavities, using complex noseleaf structures to quickly and precisely alter the beam-form and direction of emissions. Additionally, each species utilizes a unique combination of constant-frequency (CF) and frequency-modulated (FM) ultrasonic signals with varying durations, repetition rates, and frequencies. We plan to trap several species of wild Bornean bats of these genera and fly individual bats through the tunnel; a time-of-arrival algorithm will be used to localize the position of each bat at the time of each biosonar pulse emission, and an amplitude-comparison method to measure the horizontal and vertical direction of each emission from the bat’s noseleaf. We will also incorporate relatively simple foliage obstacles into the tunnel; this will create complex acoustic clutter and allow us to determine how bats of different species adjust their biosonar sampling strategies in order to navigate around novel obstacles in a cluttered environment.
In addition to remarkable acoustic sensing and navigation abilities, bats are highly agile and capable fliers, achieving flight efficiency that exceeds that of not only the rest of the animal kingdom, but of all robots as well. We seek to design a robot inspired by the biological capabilites of bats to achieve artificial flapping flight integrated with an acoustic sensing ability. Coupled with the kinematic and dynamic data collection array, we define a process for optimizing the design of bat wings for efficient flight. We identify fitness functions such as flap speed and air subtended throughout a wing cycle and then optimize the size and shape of a wing to achieve desired setpoints of the fitness functions. An inverse kinematics design process can then be used to create a single degree of freedom cyclic mechanism that will achieve the desired wing flap and fold functions. By setting fitness function objectives for both engineering design requirements (weight, lift, aerodynamics) and biologically inspired goals (wing flexibility, similarity to bat flight, responsiveness to echolocation). With this we can procedurally design a bat robot based on updating understandings of bat flight and navigation, leading to a streamlined production process when combined with rapid manufacturing.
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