# Validation of Cable-Driven Experimental Setup to Assess Movements Made with Elbow Joint Assistance
## 1 Introduction and Literature  
Robotic assistance can play an important role in the rehabilitation of stroke patients [1, 2] by assisting in repetitive movements, enabling neuroplasticity, and aiding recovery [2, 3, 4, 5]. After a stroke, the patient often suffers from hemiplegia. The earlier they undergo rehabilitation, the more likely they are to regain at least partial mobility. For both upper and lower limbs, robotic devices like exoskeletons can be a formidable tool for pre-learning movement and gesture. Research has demonstrated the benefits of using exoskeletons to facilitate exercises [6], which are essential for activities of daily living (ADLs), where repetitions are a key component of effective rehabilitation [5, 7, 8]. In addition to stroke rehabilitation, exoskeletons are also applied in fracture rehabilitation for upper limbs [9] and lower limbs [10]. Exoskeletons, due to their rigid nature, may restrict the available natural degrees of freedom of the assisted joint, thus leading to degeneracy, and this may increase existing muscular disorder [7, 11]. In this regard, cable-driven exosuits have gained attention due to their inherent flexibility [8, 12],and do not restrict any natural joint movement thus avoiding degeneracies [13; 14]. Fabric-based designs, in particular, offer simplicity and flexibility, making them well-suited for rehabilitation purposes [15]. Fabric-based cable-driven exosuits function by attaching anchor points to straps, which are then pulled by cables to induce movement [16; 17]. Tension transmission in cable-driven systems can occur via pulley systems or tendon-sheath mechanisms [18]. Tendon-sheath systems are particularly useful for remote force transmission in confined spaces, whereas pulley systems offer direct force application with reduced friction. This kind of exosuit actuation could be applicable to most joint motions, such as the elbow joint, knee, ankle, etc. [1], since its movement occurs primarily in a single plane. However, to optimize the performance of such devices, it is important to analyze key physical variables [19] such as cable tension, moments at the anchor points, and reaction forces. These factors vary depending on the load and the placement of the anchor points relative to the joint for the same load [20]. In other words, the design of the exosuit will affect these variables. For repetitive tasks, these forces may lead to wear and tear on the exosuit and subsequently reduce the performance of the device. These variables will also be important in designing with considerations for human safety and comfort [21]. Various models of exosuit actuation often assume a static approach [22; 23]. For instance, CADEL (CAble-Driven ELbow assisting device) [24] demonstrated the computation of string length and cable tension for fixed anchor points, while kinetostatic analyses of similar devices were also conducted in other studies [25; 26; 27]. However, they missed studying tensions and moments at various combinations of anchor point positions. We focused the study on the elbow joint because the literature reported studies on joint position during daily activities with a particular focus on elbow movement. [PERSON] et al. [28] examined tasks involving elbow flexion, while [PERSON] et al. [29] analyzed various tasks requiring only elbow flexion, such as eating, typing, and using a doorknob. Although these tasks involve forearm rotation, the actuation of the elbow joint and forearm rotation is independent; thus, studies on either can be conducted separately. Since reaching is carried out by elbow flexion-extension, only elbow actuation is studied in this paper. Elbow flexion occurs in the sagittal plane; the gravitational forces can be assumed to act within this plane when designing an exosuit. In the proposed work, an experimental setup with a two-rigid-bar mechanism, which mimics the human arm with an elbow joint, has been developed to investigate the performance of a fabric-based cable-driven exosuit that can be designed for elbow actuation in the future.