Improving Speed Characteristics of High-Torque-Density Motors for Physical Human–Robot Interaction Using an Independent Three-Phase Winding Structure

Round 1

Reviewer 1 Report

·        Abstract – Both types of connections should be referred to by the letter (Y, D) or by the full word (wye, star, delta), do not mix these conventions. Correct also throughout the paper, e.g. in line 60 etc.

·        Line 33 – It is arguable if this is THE primary reason. Others might have the opinion that it is the lack of sufficiently robust real-time processing algorithms which can enable autonomous robot operation. Please reword or give specific references which prove that it is indeed the primary reason.

·        Fig. 1b – It is not clear what is shown in Fig. 1b. Is this a cross-section view (how can the internal part be visible from the outside)? Describe in more details to clarify.

·        Table 2 – The torque density is specified for an unhoused motor, which is too optimistic because the motor cannot be used without its housing. At the very least both quantities should be given (torque density with and without the housing).

·        Eq. (4) – Variables V and Kt not introduced or described.

·        Eq. (5) – Variable t not introduced or described.

·        Lines 96 onwards – It is stated that the Y connection is preferred because of the higher torque. In the ordinary 3-phase machines it is well known that when operating from the same voltage source the D connection gives more torque that the Y connection, because in D full phase-to-phase voltage is applied across the a given coil, whereas in Y each coil sees only a proportion of the phase-to-phase voltage. Please explain why this statement is true, especially when compared to ordinary (e.g. induction) 3-phase motors. This is also contradicted by the text itself in lines 119-129, and further in the showed graphs and tables.

·        Second figure has a wrong number, because it should be Fig. 2, not Fig. 1. Consequently, all following Fig numbers are incorrect.

·        Eq. 10 – Is this kt constant (lower case) different from the Kt (upper case) mentioned above? Explain in the text.

·        Line 177 – The reference should be probably made to Table 3, not Table 1?

·        Line 192 – Reference to incorrect Table.

·        The (incorrectly numbered) Fig. 4(b) and Fig. 5(b) both show “connecting schematic” which is kind of meaningless because without knowing how the wires are routed internally around the magnetic core the location of the terminating wires does not change much. These pictures should be clearer in showing how the terminations as made with respect to the individual coils (for example). All drawings and diagrams should be clear enough so that any reader should be able to reproduce it. Remember that you are writing the paper for the reader, not for yourself.

·        Line 206 – There should be space between the value and its unit.

·        Eq. (4) – Variable m1 not introduced or described.

·        Eq. (5) – Variable t not introduced or described. Note that in earlier equations t was used probably as designation of continuous time, whereas in (5) it implies a different meaning. The same symbol should not be used to represent different meanings, so this should be corrected.

·        Table 5 – Is this correct that the sampling time is 0.04 sec? This sounds like a relatively long time? Explain in the text.

·        The paper should include comparison of the torque data obtained for 3 configurations, since it was the torque improvement that was the main premise of the paper.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper examines high torque density motors such as proprioceptive actuators. Since the torque density is still insufficient for physical interaction with humans, the authors attempted to develop an engine with a higher torque density. However, high torque density motors have the disadvantage of lower speed characteristics due to the increased back-EMF. To address the deterioration of speed characteristics in the developed motor, the authors used an independent 3-phase winding structure. As a result, through comparison with Y-Connection and Delta connection, the most suitable winding design for high torque density motors intended for physical interaction with humans was developed.

 1.      Replace sentences in the personal form with the passive voice, e.g. "We developed" with "was developed".

2.      There is probably a lack of time in formula (9).

3.      There is no need to show the engine structure in Fig. 5, unless the authors connect it to the proposed inverter.

4.      The authors showed the steady-state values of speed and current in the experimental results. No time waveforms from the converter are shown. There is no in-depth analysis of how the system works. Indicating only the speed without indicating the developed torque or other properties is too little for a scientific article.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

All my suggestion has been taken into account and indicated problems have been solved. Additional comments, which have been added on a request of the other reviewers and editor also improve the scientific level of the paper. Therefore, in my opinion, the paper in the current version is suggested to be accepted in Actuators  journal.