## 1 Introduction
Studies have shown that the use of robotic rehabilitation devices, when used for post-stroke rehabilitation of the upper limb, can:  
* help improve the motor control, strength, and function of the upper limb [4; 29; 34; 35], particularly if assistive, active, or resistive training modalities are being used [32; 34; 36];
* have a beneficial effect on excessive muscle tone or spasticity and pain [37];
* positively affect the patient's progress, regardless of the rehabilitation stage [32];
* have a comparable or even superior impact on the rehabilitation progress compared to the traditional approaches [18; 35; 38; 39]. However, many studies related to the post-stroke robotic rehabilitation of the upper limb primarily focus on the proximal arm joints, i.e., the shoulder and elbow, rather than the distal joints of the arm, i.e., the wrist and hand joints. The latter is interesting, as it has been found that therapeutic exercises for the distal arm joints can lead to functional improvements in both proximal and distal arm function [30; 31; 32]. Moreover, to improve the performance of ADL--reaching, gasping, manipulating, and carrying objects--the distal part of the arm must be included in the exercise protocol [22; 40], as the functional improvements of the wrist and hand alone can significantly impact the functional improvement of the whole upper limb [41]. In addition to the frequent occurrence of spasticity, the problem of successful rehabilitation of the upper limb function may be that the onset of the distal arm joints' movement recovery, compared to the proximal arm joints, usually occurs later. This delay means that even when patients regain strength and coordination in the shoulder and elbow joint, the function of the wrist and fingers is usually not yet restored, which further limits the ADL [42]. Patients especially wish to restore the ability of fine manipulation--writing, card playing, knob manipulation, and driving. Such manipulations require a coordinated action of several joints and muscles of the upper limb, particularly the wrist and hand joints [36]. Patients should continue to perform the therapeutic exercises even after discharge from the hospital. Lately, alongside robotic devices in rehabilitation, telerehabilitation technologies are also becoming increasingly used, especially in the neurological rehabilitation field. Compared to the traditional rehabilitation approaches, some of their most significant advantages are the reduced cost of the health care providers and enabling the patients to perform physiotherapy at home. The latter is especially beneficial for patients who have severe disabilities or live in rural areas and therefore could not as easily access the traditional rehabilitation services [43; 44]. Given the fact that many hospitals and clinics discharge patients when they relearn how to walk--even if the function of the upper limb, especially its distal parts, has not yet been restored [9]--an appropriate rehabilitation device, designed for an out-of-clinic use, might help them to further recover the distal arm function. The device should provide therapeutic exercises for the wrist and fingers, such as flexion and extension of said joints. It should also have an adjustable level of assistance, motivate the patient by combining exercises with playing games during therapy and providing visual feedback, monitor therapy progress, enable independent use at home or in a nonclinical setting, and have relatively low manufacturing cost [33]. The state of the art shows multiple possible solutions regarding the design of such devices. Many patent records use wearable mechanical systems in the form of a glove or a soft splint covering the forearm, hand, or fingers. There are different moving segments, such as bars, pulleys, or belts, placed on the glove or splint alongside the hand and fingers. An actuator, usually placed on the forearm portion of the arm, moves the said segments back and forth, which results in the mobilisation of either one or more fingers or the wrist [45; 46; 47; 48].