Development of Point-to-Point Path Control in Actuator Space for Hydraulic Knuckle Boom Crane
Round 1
Reviewer 1 Report
The paper presents a trajectory generation and tracking control method and applies it to motion control of hydraulically actuated cranes.
The actuator modeling and control aspects are correctly presented, while the trajectory generation relies on rather simple ideas, namely the generation of trapezoidal velocity references for multiple degrees of freedom, synchronized to obtain zero end velocity at the same instant on all DOFs.
Simulation and experiments are adequate for the scope of the paper.
However, a major concern arises from some statements of the authors, in which it is said that by controlling the system in actuator space all the parameters and constraints becomes linear. Actually, what the authors have done is simply to NEGLECT the nonlinearities of the fully coupled mechanical system. The proposed approach is in the end what is generally called "decentralized control" in robotics, in which each joint / actuator is independently controlled (e.g. by a PID regulator) and the controller is tuned to reject at its best the cross-couplings among joints. However, the effects of joints coupling, nonlinear gravity and inertia terms in the full dynamics of the crane DO NOT disappear by controlling the system in actuator space. Indeed, other so-called "centralized" approaches in robotics directly address such nonlinearities by means of inverse dynamics methods.
This aspect is crucial and must be remarked in a revision of the paper. Moreover, it is also unclear if such nonlinear coupling effects, though neglected explicitly in control design (I assume that the optimization process described by the author is suitable to obtain a proper nonlinear couplings rejection), were considered at least in the simulations. In other words, did the authors simulate the full mechanical system or simply three independent hydraulic actuators? If the first applies, which were the mass properties of the simulated crane (at least mass and center of gravity of each link)? And in the experiments, where the full crane assembled and tested for validation? Again, which were its mass properties?
Author Response
please see the attachment
Author Response File: 
Author Response.pdf
Reviewer 2 Report
In this paper an HMF 2020K4 loader crane has been used as a testing platform for path control. By using a time domain simulation model of the crane, a path generator algorithm and control algorithm have successfully been developed and implemented.
In general, authors present a path control in actuator space fort a crane. Authors should consider the following comments to clarify the main contributions of their paper.
1.- In the page 2, in the introduction, authors say "For non-redundant manipulators, tool point control is typically done using inverse kinematics, [1]. By supplying a desired tool point position, the joint angles for the manipulator can be calculated." in this part, they should include references [a], [b], [c], [d] which also use the inverse kinematics to the tool pint control of manipulators.
[a] Robust feedback linearization for nonlinear processes control, ISA Transactions, Vol. 74, pp. 155-164, 2018.
[b] Structure Regulator for the Perturbations Attenuation in a Quadrotor, IEEE Access, Vol. 7, No. 1, pp. 138244-138252, 2019.
[c] Echo State Network for Extended State Observer and Sliding Mode Control of Vehicle Drive Motor with Unknown Hysteresis Nonlinearity, Mathematical Problems in Engineering, Vol. 2020, pp. 1-13, 2020.
[d] An Electricity Generator Based on the Interaction of Static and Dynamic Magnets, IEEE Transactions on Magnetics, Vol. 55, No. 8, pp. 8204511, 2019.
2.- In the page 10, in the section 4.2, authors should describe the control structure with equations.
3.- In the page 11, in the section 5.1, authors should describe the simplified genetic algorithm with equations.
4.- In the page 12, in the section 5.2, if it is possible, authors should compare their method with other previous.
5.- In the page 16, in the conclusions, authors should include some future research.
Author Response
please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The paper has been reworked to address the concerns of the reviewer.
One last doubt is now related to the very last sentence that was added in the Conclusion of the new version. What is exactly the kind of redundant manipulators that the authors aim to address? If they refer to robots similar to the Kuka LWR or the Franka Emika Panda industrial robots, that are the kind of robots that come in mind then "redundant robots" are mentioned, I do not believe that they are a suitable application domain for the proposed control methods.
On other words, please specify better the context of your future works, that should be probably remain within the crane-like structures addressed so far.
Author Response
Please see attached document
Author Response File: Author Response.pdf
Reviewer 2 Report
The reviewer does not have more comments.
Author Response
Please see attached document
Author Response File: Author Response.pdf
