## 3 End Effector-Based Devices for Gait and Balance Rehabilitation
### Review of End effectors
#### 3.2.2 Non-Commercially Available End Effectors  
Compared to the number of the aforementioned commercialized devices, a significant number of prototypes and theoretical designs of end effectors were found in the literature. Namely, 39 end effectors were proposed among different research groups and authors. Depending on the type of mechanism that they use for moving the footplates and thus to generate the rehabilitation movements, these end effectors can be divided into two groups: those that use parallel kinematic manipulators (PKMs), and those using another kind of mechanisms (e.g., slider-crank and serial robots). **-Driven by PKM**. The non-commercially available end effectors driven by PKMs are presented in Table 2. All of them have the advantages of parallel mechanisms, such as excellent positioning accuracy, high stiffness, compactness, and a high payload/mass ratio [130]. Moreover, the entire mechanism can be confined below the footplates, avoiding possible collisions with the patients, and the actuators can be placed on the fixed frame, which reduces the inertia of the device (lower energy consumption). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Device** & **Ref** & **DOFs** & **Objective** & **Training Mode** & **Company** \\ \hline Gait Trainer-GT I & [114] & \(1\times 2\) & Gait & Hybrid & Reha-Stim (Germany) \\ Gait Trainer-GT II & [115] & \(1\times 2\) & Gait & Hybrid & Reha-Stim Medtec (Switzerland) \\ LEXO® & [116] & \(1\times 2\) & Gait & Hybrid & Tyromotion (Austria) \\ Lyra & [117] & \(1\times 2\) & Gait & Passive & THEERA-Trainer (Germany) \\ Morning Walk & [118] & \(3\times 2\) & Gait & Hybrid & CUREXO, Inc. (South Korea) \\ G-EO system & [119] & \(3\times 2\) & Gait & Hybrid & REHA Technology (Switzerland) \\ Hunova® & [120] & \(2\times 2\) & Balance & Hybrid & Movendo Technology (Italy) \\ Balance SystemTM SD & [121] & 2 & Balance & Active & Biodex Medical Systems, Inc. (USA) \\ DynSTABLE & [122] & 2 & Balance & Passive & Motek Medical (The Netherlands) \\ Huber 360® & [123] & 2 & Balance & Passive & LPG Systems (France) \\ GeaHD & [124] & 2 & Balance & Passive & Vertigomed (Italy) \\ PROPRIO® 5000 & [125] & 2 & Balance & Passive & Perry Dynamics, Inc. (USA) \\ Smart EquiTTest® & [126] & 2 & Balance & Passive & NeuroCom International, Inc. (USA) \\ ProKin & [127] & 2 & Balance & Active & TecnBody® (Italy) \\ MultiTest Equilibre & [128] & 6 & Balance & Active & FRAMIRAL (France) \\ CAREN & [129] & 6 & Both & Passive & Motek Medical (The Netherlands) \\ \hline \hline \end{tabular} DOFs, degrees of freedom (\(\times 2\) = two footplates). The training mode is from the patient’s point of view, that is, “active” means that the patient takes part in to generate movement of the footplates, whereas “passive” means that the device moves the footplates without the collaboration of the patient.  
\end{table} 
Table 1: Commercialized end effector-based devices for gait and balance rehabilitation. However, one major drawback of using PKMs is their limited workspace. In particular, the size and shape of the workspace are critical for those end effectors with gait rehabilitation purposes, in which a sufficient step length/height must be achieved to mimic human gait trajectory. One of the most straightforward ways to tackle this problem is to increase the dimensions of the PKM, but this solution would lead to bulky designs. That is why some of the currently available prototypes, instead of increasing the size of the design, use a PKM with prismatic joints to overcome this problem, like in the 3-PRR proposed by [PERSON] et al. (2013), where P and R stand for prismatic and revolute joints, respectively, while the underlined letter indicates the actuated kinematic joint. Another way to increase the workspace is to combine a linear guide serially with the PKM, i.e., connect the PKM, which moves each footplate, above a linear guide that allows displacement along the anterior-posterior (longitudinal) direction. The P-(PR-PRP) PKM developed by [PERSON] et al.