This research was derived from the experimental observation that hydraulic actuators are positioned on machines that are subjected to movements and whose dynamic actions, the accelerations, are very high; it is acceptable to think of an actuator for an anthropomorphic robot. From this point of view, the weight of the actuator plays a fundamental role in the performance of the machine. In order to face this problem, a real hydraulic cylinder has been designed (for use on an earth moving machine) both analytically (adopting the theories of continuous mechanics) and numerically through finite element analysis. The results obtained were then generalized by determining functions that in relation to specific values of the variables, such as working pressure, allow one to determine the minimum weight of the component and its geometric configuration. The functions also made it possible to identify the most significant contributions to the overall weight of the component and therefore the elements on which to focus the subsequent lightening process. In particular, the greatest contribution is made by obtaining relations that are completely general and therefore adaptable to different case studies.

Usability is a critical product feature and is required for widespread market adoption. Standards on usability are highly focused on evaluation procedures and specific aspects, such as software issues or human–machine interaction, whereas the relative scientific literature is very normative oriented. The few methodological works dealing with usability either consider it as one of the many attributes that a particular project must satisfy or present very general methods. No design methods systematically oriented toward the integration of usability and usability-related constraints have been developed to date. This paper presents a usability-oriented model for the design of medical devices and its application to the design of LEPRE, a medical device for upper- and lower-limb robotic rehabilitation. Two methods were used to assess the device’s usability: interviews with experts to outline qualitative evaluations and System Usability Scale (SUS) questionnaires on eight physiotherapists, two physiatrists, and 12 patients, enabling a quantitative assessment. Results support the intention of providing an integrated methodological approach to be applied from the early stages of the project, thus saving time and costs, leading to a more linear product development for this application.