# Neural Approximation Enhanced Predictive Tracking Control of a Novel Designed Four-Wheeled Rollator
## 6 Points for Future Discussion  
The assistive rollator system we developed for the elderly rehabilitation and disabled users is currently being considered to be industrialized in China and some European countries, implementing convenience for the users to walk and to run safely.  
How to develop an elderly rollator with a standard concept is a prerequisite. Rollators for the disabled and rehabilitation patients occupy a significant market, and the demand for elderly walkers caused by the aging society has not been satisfied. In the traditional product innovation method, the technical personnel usually solve the contradiction in a compromised manner for the existing conflicting internal technical characteristics of the product. However, this method does not solve the actual needs of elderly mobility vehicles, which limit the performance of the product. However, the TRIZ theory is a systematic and creative innovation method.  
Figure 15: The comparative results of NMPC and MPC in longitudinal position, lateral position, roll angle, rollator velocity, longitudinal error, and lateral error.  
How to combine the concepts of TRIZ, QFD, and Kano to design a walker is the main work. In this paper, TRIZ is used to solve the technical characteristics of the product, the user needs obtaining through surveys, and the types of requirements analyzed using the Kano model. At the same time, the Kano model only analyzes the shortcomings of user needs. The House of Quality (HOQ) in QFD is a useful tool for converting customer needs into design requirements. In this way, the technical needs and user needs can be well combined to design a mobility product that meets the physical and mental health of the elderly.  
How to improve the safety assistance system of the rollator equipment is the challenge. As medical devices, elderly mobility aid has extremely critical security conditions. There is an unknown disturbance in the process of the rollator operation, such as uneven terrain, the uncertain mechanism, etc.. Meanwhile, in our previous work, we discussed the autonomous tracking control of a four-wheel rollator, but this study did not consider dynamic interference. Based on this, in this article, we manage to develop the controller to improve the safety and stability under uncertain physical interaction.  
Finally, the elderly mobility aid is medical rehabilitation equipment, and it is an essential tool for the disabled and the elderly to travel. Future work, including the design of mechanical structures, control systems, human-robot interaction, and intelligent control, will be considered to enhance the design of walking vehicles further.  
Conceptualization, J.L. and X.Z.; Data curation, K.F. and Z.C.; Formal analysis, Z.H.; Investigation, Z.C. and Z.H.; Methodology, J.L. and X.Z.; Project administration, J.L. and X.Z.; Software, K.F. and Z.C.; Supervision, X.Z. and Y.Y.; Validation, K.F.; Writing--original draft, J.L. and X.Z.; Writing--review editing, J.L. and X.Z. All authors have read and agreed to the published version of the manuscript.  
This research is supported by Chinese Scholarship Council under Grant: 201906030066.  
The authors declare no conflict of interest in the collection, analyses or in the decision to publish the results.  
The following abbreviations are used in this manuscript:  
Model Predictive Control  
Radial Basis Function Neural Network  
Theory of Inventive Problem Solving  
Quality Function Deployment  
House of Quality  
Proportion Integration Differentiation