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Working with forestry cranes is not easy due to their complex mechanical structure, non-linear behavior of the hydraulic actuation system, and non-intuitive joint-based control; however, with automation, the level of manipulation difficulty can be reduced. This is potentially useful for the operators since they are prone to be more productive if semi-automation functions are introduced to a certain level. In this paper, a semi-automation function for the base joint actuator of a forestry forwarder crane is proposed. The semi-automation function is based on a design of an interactive on-line trajectory generation algorithm with variable final time that acts as a reference signal to a closed-loop position controller. Moreover, the advantage of this scheme is that the operators are kept in the loop by directly being in charge of controlling the final time for the on-line trajectory generation algorithm. Experiments with a downsized industry-standard forwarder crane verify the applicability and advantage of the proposed scheme.

In this work an interval observer is proposed for on-line estimation of differentiation errors in some class of high order differentiators (like a high-gain differentiator from [26], or homogeneous nonlinear differentiator from [24 or super twisting differentiator [15]). The results are verified and validated on the telescopic link of a robotic arm for forestry applications in which the mentioned approaches are used to estimate the extension velocity while the interval observer gives bounds to this estimation.

A methodology based on an equation of motion and a two-steps off-line optimization procedure is proposed and investigated to estimate a payload in an industry-standard Front-End Loader. The location of the boom center of gravity is first calibrated via optimization using a known payload to become the base to estimate an unknown payload. This method is compared to an existing method and is verified to be less sensitive to different estimation conditions. Moreover, it also requires less additional operations in the calibration phase.

Simplifying the operation of forestry machines with operator-centered semi-automation is needed in the modern timber harvesting industry in order to increase operator productivity and comfort, to reduce learning time of novice operators and to ensure safer manipulation of the cranes. In this paper, useful tools towards operator-centered semi-automation of the base joint actuator of a forwarder crane are proposed. The main goal is to allow comfortable automated motions that do not excite dangerous oscillations of the freely-hanging grapple. Moreover, operator commands are used interactively with a closed-loop position control scheme to assure automated slewing motions. Smooth reference trajectories are provided for the position controller with an on-line trajectory generation algorithm that is developed by combining properties of two standard trajectory generation methods. A practical algorithm based on experiments is introduced to find the trajectory that guaranties minimal grapple oscillations within a set of relatively fast trajectories. Further on, the log loading/unloading tasks are discussed and verified experimentally using the proposed approach on a forwarder crane prototype.

In mobile hydraulic systems, velocities are typically not measured. However, using their reliable estimates for feedback is known to allow designing better control laws. We are going to present a specialized technique to compute such estimates using measurements of positions and pressures in the chambers of hydraulic cylinders. With a rough estimate for an upper bound of the second derivative, computed online from pressures, the goal is to find the first derivative of the position signal in the presence of noise. We propose a differentiator with a continuous time-varying gain, constructed from pressure measurements, achieving chattering attenuation without compromising the performance of estimation. The gain is constructively tuned using analysis based on a time-varying Lyapunov function. In addition, the obtained ultimate bounds on differentiation errors provide a criterion for the enhancement of the precision of the proposed algorithm with a constructive design of its parameters. The experimental results over a forestry-standard mobile hydraulic crane confirm the advantages of the methodology.

Smooth operation of heavy-duty forestry cranes is not an easy task for the operators with the current joystick-based control method that is complex and non-intuitive. Moreover, abrupt movements of the same joysticks provoke aggressive signals that can lead to oscillatory motions in the actuators and in the entire crane. These oscillations, not only contribute to wear of the joint actuators but also can cause damage to both the operators and the environment; therefore, they must be attenuated. The proposed approach in this paper uses the popular input shaping control technique combined with a practical switching logic to deal with different frequency payload oscillations induced by the motion of the inner boom actuator of a forwarder crane. The results show a significant improvement in terms of visible oscillation reduction monitored through their appearance in the torque signal computed from pressure measurements. Experiments performed on a down-sized forestry crane verifies the effectiveness of the approach.

Due to some limitations of mechanical solution for automation of front end loaders, specifically self-leveling task, we investigate here the sensor-based solution. We present a model of ront end loaders and the comparison of different controllers to realize this task. The best performance is observed from the controller comprising linear terms, compensation of input nonlinearity known as dead zone, and compensation of disturbances from its estimation.

The modern timber harvesting industry would be ineffective without heavy duty advanced machinery used for logging. However, with benefits of mechanization comes the operation complexity. Introducing automation is expected to reduce the mental and physical load on the operator and improve the machine use efficiency. Nonetheless, with current technology fully autonomous timber harvesting is impossible. In this paper a semi-automation scenario is presented using the base joint actuator of a forestry forwarder crane taking into consideration the need to attenuate unwanted oscillations of its hanging grapple. We address the necessary motion planning and motion stabilization tasks. To reduce oscillations along a nominal trajectory, we design smooth reference profiles based on experiments. Meanwhile, a practical structure for a feedback controller is proposed and tested. In this process, actuator nonlinearities are dealt with feasible identification and compensation techniques.

This work addresses the stabilization of dynamical systems in presence of uncertain bounded perturbations using epsilon-invariance theory. Under some assumptions, the problem is reduced to the stabilization of a chain of integrators subject to a perturbation and is treated in two steps. The evaluation of the disturbance and its compensation. Homogeneous observer and control [5], [19] are the tools utilized to achieve a global asymptotic stability and robustness. The result is formally proven and, to validate the theory, it is applied to the control of the telescopic link of a hydraulic actuated industrial crane used in forestry. Experimental results and a comparison with a standard PI controller are presented.