Functional Safety Analysis and Design of Sensors in Robot Joint Drive System

Round 1

Reviewer 1 Report

This is a paper proposing a functional safety analysis and design methodology for sensors in robot joint drive systems (RJD) according to IEC 61508.  Hazard analysis and risk assessment are used to define the goals to be achieved by the safety protection function of the RJD sensors. A model-based sensor fault diagnosis and isolation strategy is proposed and its effectiveness is demonstrated through experiments. A safety-related system architecture is designed and the SIL of the architecture is obtained by Markov analysis.

This paper is about techniques for safety design for cooperative robots and is of high importance. The reviwer did not find any significant technical problems with the content of the paper.

On the other hand, the novelty of the proposed technology is not so clear.
The authors point out that the problem with conventional techniques for redundancy and sensor fault diagnosis is that they do not pay attention to functional safety aspects. In contrast, the authors claim that based on IEC 61508, the proposed method systematically analyzes sensor failures in RJDs.
However, commercially available industrial robots are designed in
accordance with ISO 10218-2. Their safety-related control systems (electrical, hydraulic, pneumatic and software) are in accordance with PLd as specified in ISO 13849-1 or SIL2 as specified in IEC 62061, unless a risk assessment determines that an alternative is appropriate.
In other words, the industrial robots are already paying attention to functional safety.
Therefore, the novelty of the proposed method in this paper should be discussed in comparison to safety-related control systems for industrial robots compliant with ISO 10218. Not only compared to individual academic redundancy and fault diagnosis techniques.

Optional comments:

• The explanation of the required SIL in section 2.2 should refer to ISO 10218-2.
• Chapter 3 should be carefully changed to a description that clarifies the novelty. The proposed mathematical models (6) and (8) seem self-evident. The description should be revised to clarify that the mathematical models are newly proposed in this paper in comparison with existing techniques and models. 

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper conducts a comprehensive analysis and design of the sensor functional safety of robot joint drives based IEC61508.

The paper covers an important point, has a clear structure and is nice to read.

However, a few weaknesses should be addressed:

• All abbreviations must be explained in the text e.g. FOC, MCU, AC, SVPWM
• Figure 1 should be accompanied by a less abstract representation; e.g. a figure showing an exemplary geometrical realization of a RJD as well as its integration in a full robotic system
• The usage of the terms failure and fault is not consistent (example in line 363). Clear definitions taken from literature concerning fault-tolerant control and fault-tolerant design should be used and explicitly given in the introduction.
• For the equations in section 5 sources need to be given
• Few mistakes: e.g. line 498 “encoder angels”

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

No new comments.