As a reviewer I appreciate the hard work you are contributing to curate this article.
Minor grammatical note: When used as an adjective in English, there should be no hyphen in “light-weight” robot. Instead, the article title should be “lightweight” robot.
Major general point: Is it possible to acknowledge two competing design approaches for lightweight arms? Although most lightweight robot arms (e.g. DLR, Mitsubishi’s PA10, Robonaut) follow the *Design Approach* reported in the present article, there is a branch of lightweight arms that follows a distinctly different design approach, represented by the WAM arm and the Mako Surgical HGS [Nasdaq: MAKO], in which greater emphasis is placed on reducing backdriven inertia and increasing the bandwidth of torque control. I added two citations to your reference list that discuss the alternate approach.
Other general points: 1. The article is called “lightweight robots” and it is clear from your mention of the importance of lightweight robots for space use that the *system* mass to be taken to orbit (or beyond) is important. So my question is: What constitutes the lightweight-robot system? Does it include high-level controllers, power supplies, etc.? 2. I did not see mention of power consumption in your article, but that would seem important for space applications and most mobile applications. Can you discuss this aspect of lightweight robots? Does DLR have any analysis equating watts of average consumption with kilograms of additional solar-panel area? 3. By definition, sensor collocation means that there are no significant dynamics between the actuator and the sensor. You mention in the DLR control example (last paragraph of the section) that you consider the torque sensor to be collocated. But early in that section you highlight (in the second bullet) the friction (between the actuator and the sensor) and (in the third bullet) “the elasticity of the transmission” and gear-induced dynamic vibrations. Can you sort this apparent discrepancy? 4. While the concept of modularity is powerful and important, what limitations does modularity place on achieving low weight?
I hope you find these comments useful.
Nicely written and clear article. It would be ideal to give examples of control approaches of other arms (Barrett, etc.), and compare and contrast with DLR, as the article currently seems biased towards DLR. That being said, I have made some minor corrections in the text, and can accept the article as is.