Metin Yilmaz

SURALP: A new full-body humanoid robot platform

SURALP is a new walking humanoid robot platform designed at Sabanci University - Turkey. The kinematic arrangement of the robot consists of 29 independently driven axes, including legs, arms, waist and a neck. This paper presents the highlights of the design of this robot and experimental walking results. Mechanical design, actuation mechanisms, sensors, the control hardware and algorithms are introduced. The actuation is based on DC motors, belt and pulley systems and Harmonic Drive reduction gears. The sensory equipment consists of joint encoders, force/torque sensors, inertial measurement systems and cameras. The control hardware is based on a dSpace digital signal processor. A smooth walking trajectory is generated. A variety of controllers for landing impact reduction, body inclination and Zero Moment Point (ZMP) regulation, early landing trajectory modification, and foot-ground orientation compliance and independent joint position controllers are employed. A posture zeroing procedure is followed after manual zeroing of the robot joints. The experimental results indicate that the control algorithms presented are successful in improving the stability of the walk.

Trajectory generation with natural ZMP references for the biped walking robot SURALP

Bipedal locomotion has good obstacle avoidance properties. A robot with human appearance has advantages in human-robot communication. However, walking control is difficult due to the complex robot dynamics involved.

Humanoid robot walking control on inclined planes

The humanoid bipedal structure is suitable for a assitive robot functioning in the human environment. However, the bipedal walk is a difficult control problem. Walking just on even floor is not satisfactory for the applicability of a humanoid robot. This paper presents a study on bipedal walk on inclined planes. A Zero Moment Point (ZMP) based reference generation technique is employed. The orientation of the feet is adjusted online by a fuzzy logic system to adapt to different walking surface slopes. This system uses a sampling time larger than the one of the joint space position controllers. The average value of the body pitch angle is used as the inputs to the fuzzy logic system. A foot pitch orientation compensator implemented independently for the two feet complements the fuzyy controller. A 12-degrees-of-freedom (DOF) biped robot model is used in the full-dynamics 3-D simulations. Simulations are carried out on even floor and inclined planes with different slopes. The results indicate that the control method presented is successful in enabling the robot to climb slopes of 8.5 degrees (15 percent grade).

Fuzzy controller scheduling for robotic manipulator force control

Force control of robotic manipulators is becoming more and more important in applications that involve interaction with the environment. Depending on the nature of the task at hand, different control algorithms can be suitable to be implemented. In this paper the task of reaching an object by the robot tool and applying a constant force on it is considered as a case study. This task is one of the typical manipulation operations. A fuzzy logic scheduling approach, which smoothly changes the control action between two force control schemes, is proposed. The first force control method is admittance control, which is suitable to be used in the phase of approaching the work piece. The second one is an explicit force control strategy, integral force control, suitable for force regulation when the manipulator tool is in contact with the work piece. The fuzzy controller scheduling approach is tested via experimental work on a direct drive SCARA-type manipulator. It is also compared with a crisp controller switching method. Experiments are carried out with fixed and free-to-move work pieces. The results validate that the proposed fuzzy transition has advantages over a crisp switching between controllers.

Walking Control of a Biped Robot on an Inclined Plane

The human structure is suitable for an assistive robot in the human environment. However, the bipedal walk is a challenging problem. Walking on flat and even floor conditions is not satisfactory for the applicability of a humanoid robot. This paper presents an experimental study on bipedal walk on inclined plane. The 29-degrees-of-freedom (DOF) biped robot SURALP is used in the experiments. A variety of controllers for landing impact reduction, body inclination and Zero Moment Point (ZMP) regulation, early landing trajectory modification, and foot–ground orientation compliance are employed. A posture zeroing procedure is followed after manual zeroing of the robot joints. Experiments are carried out on even floor and inclined planes with different slopes. The experimental results indicate that the control algorithms presented are successful in improving the stability of the walk.

Circular arc-shaped walking trajectory generation for bipedal humanoid robots

The design of a controller which can achieve a steady and stable walk is crucial in bipedal humanoid robotics. Reference trajectory generation is central in the walking control. The Zero Moment Point (ZMP) criterion is the most widely used stability criterion for trajectory generation. It is most successfully used when the ZMP equations are coupled with the dynamics equations of a simple mechanism, the Linear Inverted Pendulum Model (LIPM) which approximates the humanoid model. In a number of approaches the position reference for the Center of Mass (CoM) of the robot body is computed from predefined ZMP references. After the computation of the CoM, the joint references are computed by inverse kinematics. A natural ZMP reference trajectory and a Fourier series approximation based method for computing the CoM reference from it, was previously proposed for the humanoid robot SURALP (Sabanci University Robotics ReseArch Laboratory Platform), for a straight walk This paper improves these techniques by modifying the straight walk reference trajectory into an arc-shaped one. In principle the straight walk is projected into a walk reference on an arc with a desired radius. On-line smooth change of the walking direction is achieved by adjusting the arc radius command. The proposed reference generation algorithm is tested on SURALP. Experiments indicate that the method is successful in generating a stable walk following an arc.

Biped robot walking control on inclined planes with fuzzy parameter adaptation

The bipedal structure is suitable for a robot functioning in the human environment, and assuming assistive roles. However, the bipedal walk is a poses a difficult control problem. Walking on even floor is not satisfactory for the applicability of a humanoid robot. This paper presents a study on bipedal walk on inclined planes. A Zero Moment Point (ZMP) based reference generation technique is employed. The orientation of the upper body is adjusted online by a fuzzy logic system to adapt to different walking surface slopes. This system uses a sampling time larger than the one of the joint space position controllers. A newly defined measure of the oscillatory behavior of the body pitch angle and the average value of the pelvis pitch angle are used as inputs to the fuzzy adaptation system. A 12-degrees-of-freedom (DOF) biped robot model is used in the full-dynamics 3-D simulations. Simulations are carried out on even floor and inclined planes with different slopes. The results indicate that the fuzzy adaptation algorithms presented are successful in enabling the robot to climb slopes of 5.6 degrees (10 percent).