This paper presents a model-based, cascaded control structure for a balancing manipulator actuated by pneumatic artificial muscles (PAMs). The balancer is designed to offer two operating modes: First, a balancing mode (BM) compensates for the total weight of the system so that the user feels only minimal resistance when moving the end-effector (EE) during load handling. Second, a position controller (PC) stabilizes the EE at a fixed reference position, even if the attached payload abruptly changes. The proposed cascaded control architecture consists of fast inner loops that control the pressures inside the PAMs, while an outer cascade allows for switching between BM and PC. A velocity-based backstepping approach is employed for the BM. For the position-control mode, a backstepping controller is implemented, which is extended with a cubic as well as an integral error term. An experimental validation on a test rig confirmed the effectiveness of both functions.

In this paper, an assistance system with pneumatic artificial muscles for a manually guided payload handling is presented. One operation mode requires the stabilization of the end effector position during payload changes, where two alternative position control approaches are designed and investigated: flatness-based and integral sliding mode control. The proposed control structure is a cascaded one, where in the inner loop the internal muscle pressures are controlled. Two polynomial functions are identified experimentally to approximate the characteristics for the nonlinear muscle forces and volumes, whereas the equations of motion for the mechanical structure are derived using Lagrange’s equations. Both control designs are validated and compared to each other with varying payloads on a prototype of the assistance system. Experimental results indicate a good control performance.

This paper presents a Takagi-Sugeno (TS) approach for an accurate position tracking control of a hydraulic servo cylinder. Disturbances as well as noisy measurements are addressed by a state and disturbance observer designed using TS techniques as well. Both TS designs are based on a nonlinear mathematical model of the test rig. The derived quasi-linear models contain state-dependent matrices and can be reformulated as a TS fuzzy model. In this framework, the given lower and upper bounds of the nonlinearities are considered by separate vertex models belonging to a polytope. The calculation of the feedback gains as well of the observer gains for the vertex models are performed by LQR techniques. The overall control and observer gains are obtained by a weighted combination of those of the vertex models. To improve the position tracking behavior, the TS control structure is extended by feedforward control actions as well as a disturbance compensation. The benefits of the proposed control structure and the achieved control performance are shown by experimental results from an implementation on a test rig.

This paper presents a new approach for the control of a pneumatic robot dedicated to precisely reproduce the breathing-induced motion of a human lung tumor. In medical research and tumor scanner experiments, a tumor mimic model should perform the identical smooth motion as it occurs in a real human body during exhalation and inhalation. For this purpose, a serial robot with three pneumatically driven axes has been developed and built up. Aiming at a low-cost solution, only three pneumatic valves are used. Given the small chamber volumes of the pneumatic cylinders, a precise modeling and identification of the pneumatic components proves important. The proposed control approach involves a cascaded tracking control structure with fast inner control loops for the cylinder force, whereas the corresponding outer control loop handles the position control of the corresponding cylinder. Furthermore, a lumped disturbance force is counteracted by a simplified disturbance observer. The performance of this low-cost solution is validated and compared with results from a previous, more expensive design.

In this paper, a cascaded nonlinear control design for the position of a hydraulic servo cylinder is presented that is based on a control-oriented mathematical model of the test rig. The difference pressure is controlled in the inner loop, whereas the position control is addressed in the outer control loop. Additionally, the outer positioin control loop is extended by a combination of feedforward friction compensation and an observer-based disturbance compensation to improve the position tracking behaviour. Thereby, the benefits of both measures can be exploited: fast reaction and robustness w.r.t. remaining parameter uncertainties and inaccuracies in the friction model. As the system states are measurable, a reduced-order disturbance observer is designed. The efficiency of the overall control structure and the impact of the individual control actions are pointed out by experimental results obtained at a test rig at the Chair of Mechatronics, University of Rostock.

In this paper, backstepping control techniques are presented for a mechanism dedicated to accurately reproduce the breathing-induced motion of a human lung tumour. A lung tumour mimic model should perform the same smooth motion as a real one in a human body during inhalation and exhalation. Therefore, a three-dimensional mechanism with three pneumatically driven axes has been developed and built up. For each axis, the proposed design involves a cascaded tracking control structure: fast inner control loops are responsible for the chamber pressures of the corresponding pneumatic cylinder, whereas the outer control loop is related to the cylinder position. Moreover, a lumped disturbance force is addressed properly either within an adaptive backstepping scheme or by the combination of backstepping control with a sliding mode observer. These alternative control approaches have been implemented, compared to each other and successfully validated on an innovative test rig.

In this paper, a decentralized optimal control approach is proposed for the motor torque provided by a hydrostatic transmission. As basis of the control design, a nonlinear control-oriented model of the hydrostatic transmission is derived. On the one hand, the decentralized structure consists of a flatness-based control of the normalized tilt angle of the hydraulic motor, on the other, of an optimal control design of the hydraulic motor torque based on a Takagi-Sugeno (TS) approach. Given a TS state-space model, the optimal state feedback follows from local optimal designs that are interpolated by exact membership functions. Closed-loop stability is ensured by solving a set of linear matrix inequalities (LMIs) that leads to a joint Lyapunov function. Furthermore, the feedback control is extended by feedforward control to increase the tracking accuracy. An extended Kalman filter estimates the unmeasured states as well as disturbances, which are used for a subsequent disturbance rejection. Finally, the benefits of the proposed control structure are pointed out by simulations using a validated model of a dedicated test rig.

This paper presents a nonlinear model-based control design for an electro-pneumatic clutch for heavy trucks, which is required at start-up or during gear shifts to disconnect the combustion engine from the gear box. This automated actuator disburdens the driver and provides the necessary actuation force according to the large torque transmitted through the powertrain. The proposed cascaded control structure consists of a fast inner control loop for the internal pressure as well as an outer control loop for the clutch position, which is extended by a reduced-order observer. The design of the feedback part is based on backstepping techniques. A reduced-order disturbance observer estimates the internal pressure, which is usually not measured in truck applications. Thereby, high tracking accuracy is achievable for the piston position as controlled variable. The efficiency of the proposed control structure is demonstrated by experimental results from a dedicated test rig.

Oscillation attenuation is an essential task for practically any crane application. Classically, such control strategies make use of the actuation of a crane trolley to counteract the motion of a swinging payload. As an alternative to controlling trolley motions, variations of the rope length can be considered. In contrast to scenarios where trolley motions are used to attenuate oscillations, the control of the rope length is a more challenging task due to non-negligible nonlinearities and due to the presence of points in the state-space for which controllability is not guaranteed. In this paper, a novel extended linearization approach is presented for the oscillation attenuation in crane systems, where the feedback gains are determined by using a robust optimization procedure which employs a formulation of the control task in terms of linear matrix inequalities. Simulation results and an experimental validation highlight the practical applicability of the proposed control procedure.

This paper presents a decentralised control approach for the hydraulic motor torque provided by a hydrostatic transmission. Based on a control-oriented model of the hydrostatic transmission, a quasi-linear state-space representation with both state-dependent and input-dependent matrices is derived. Using extended linearisation techniques, a combined feedforward and feedback control is designed. Furthermore, a sliding-mode observer estimates unmeasurable states as well as disturbances. The estimates for the disturbances – an external load torque and a leakage oil volume flow – can be used for a disturbance rejection. The proposed overall control structure is investigated thoroughly in simulations and, afterwards, implemented as well as validated on a dedicated test rig.

The paper presents a nonlinear control design for the position of an electro-pneumatic clutch that is based on a nonlinear mathematical model. Regarding the lower and upper bounds of the nonlinear terms involved, a fuzzy Takagi-Sugeno (TS) description with four corner models in a polytopic framework can be used for the control design. The feedback control gains are calculated for each corner model, and the overall adaptive feedback gain vector results from a norm-optimal combination of the individual feedback actions of these corner models. For an improvement of the tracking behaviour of the clutch, the control structure is extended by a dynamic feedforward control as well as an observer-based disturbance compensation. Here, a lumped disturbance force is estimated by a gain-scheduled sliding mode observer. The benefits of the proposed control structure are demonstrated by experimental results from a dedicated test rig.

In this paper, a Takagi-Sugeno (TS) approach is proposed for the position control of a hydraulic servo cylinder. Based on a nonlinear mathematical model of the test rig, an exact quasi-linear model with state-dependent matrices is derived and reformulated as a TS fuzzy model. In this framework, the given lower and upper bounds of the nonlinearities are considered by separate local models belonging to a polytope. The adaptive feedback control gains are given by a weighted combination of those of the corner models. To improve the position tracking behaviour, the TS control structure is extended by feedforward control actions as well as an observer-based disturbance compensation. Here, a lumped disturbance force consisting of imperfections of the feedforward friction model and parameter uncertainty -is estimated by a reduced-order nonlinear observer. The benefits of the proposed control structure and the achieved control performance are shown by experimental results from an implementation on a test rig.

This paper presents an average value model for the real-time estimation of residual and reaspirative gas in a cylinder of an innovative diesel engine with variable valve lift. Based on a mean-value-model over a combustion cycle, the oxygen mass fraction before the combustion is calculated with information of an oxygen sensor in the intake and a lambda sensor in the exhaust manifold. Furthermore, a model for the residual and reaspirative gas mass is introduced that employs information of the cylinder gas mass, the fuel mass and the intake oxygen. The model equations are validated at an engine with a series high pressure line. Finally, a method for estimating the scavenging mass is introduced. Experimental results point out the benefits of the proposed estimation scheme.

A nonlinear control approach for an innovative engine cooling system in vehicles is presented in this paper. The electrically driven radiator fan is employed as a control input. The engine cooling system represents a special class of nonlinear systems characterized by both matched and mismatched lumped disturbances. Based on a control oriented system representation, a backstepping-based sliding mode control is designed to track desired trajectories of the engine outlet temperature. Moreover, the lumped disturbances are estimated using a gain-scheduled modified Utkin observer. Experiments at a dedicated test-rig depict the effectiveness of the proposed control scheme in comparison to a PI controller.

This paper presents a model-based tracking control design for a mechanism dedicated to accurately reproduce the breathing-induced motion of a human lung tumour. A lung tumour mimic model should perform the same smooth motion as a real one in a human body during inhalation and exhalation. For this purpose, a 3-dimensional mechanism with three pneumatically driven axes has been developed and built up. The proposed control structure represents a cascaded flatness-based tracking control structure: In the fast inner loops, the chambers pressures of the pneumatic cylinders are controlled, whereas the outer loops are related to the position control of the cylinders. Furthermore, sliding mode observers are employed for each cylinder to estimate the corresponding states and a lumped disturbance force. The proposed overall control structure has been implemented and successfully validated on an innovative test rig.

This paper presents a tracking control approach for a hydrostatic transmission system. To reduce the effort regarding control design and implementation, a decentralised control structure has been investigated in earlier research that outperformed a central one. In this paper, a new cascaded structure is proposed for the decentralised control of the motor angular velocity. For the design of all control loops, flatness-based techniques are employed. Moreover, a sliding mode observer is employed to provide a robust reconstruction of the unmeasurable system states and unknown disturbances. The proposed control structure is validated experimentally at a test rig and compared to earlier results. The outstanding results highlight the applicability and the performance of the cascaded approach.