# A Wireless Hand Grip Device for Motion and Force Analysis
## 1 Introduction
This new solution allows for a very accurate reconstruction of the pen tip coordinates and had the advantage to be suitable for handwriting and movement acquisition for pathologic subjects. The system does not measure any force done by subject over the pen tip. Additionally, the system requires higher costs than a computerized tablet and a dedicated room with trained staff. A hand tracking perspective based on magnets attached to fingers and an electronic wristband is presented in [24]. This system exploits advanced design of magnetic flux sensors and recent research on hand-based communication. It is wireless, portable, unobstructive and convenient. The proposed method considers two computational steps. The first step estimates the locations and orientations of the magnets and the fingertips from the measured flux densities; and the second step reconstructs the finger postures from the locations and orientations of the fingertips based on a geometric model of the fingers. The system is validated against a Vicom motion tracking system. In general, the estimation based on magnetic data was reasonably consistent with the direct measurement of the joint angles. Unfortunately, problems arise in the magnetic flux measurements when the system is operated near objects constructed of magnetic materials. To present the most important contribution of wearable sensing gloves, we consider the work done in [25; 26]. The first contribution presents a wearable sensing glove with embedded hetero-core fiber-optic nerve sensors that detect finger flexion to achieve unconstrained hand motion monitoring. The hetero-core fiber sensor is suited to the wearable sensing glove because it is capable of optical intensity-based measurements with excellent stability and repeatability using single-mode transmission fibers and is unaffected by temperature fluctuations. The system has been validated using a virtual reality application and the sensitivity and accuracy in the detected flexion angles are small. In paper [26], a data glove equipped with force sensors is presented. The force sensor is made of a steel plate substrate where the commercial strain gauges are attached. The plate is attached to the thumb. The system has a sensor calibrated to measure between 0 and 100 N, with a resolution of 0.38N and excellent repeatability. In any case, we consider that the system is obtrusive and needs direct connection to a PC. All of the above presented systems include wearable sensors with applications in human biomechanical and health monitoring. In order to summarize the progress and challenges in fabrication of wearable sensors, recent work done in [27] was reviewed. A similar practical application using wearable thermal sensors was presented in [28]. In tune with the above mentioned state of the art, a summary of the main objectives and research contributions of this work follows below. 1. The proposed hand grip device uses sensors, not influencing natural hand and finger movements. 2. A wireless, portable and flexible prototype hand grip device that allows simultaneous hand and fingers precise motion and force measurements is presented. 3. The device design is oriented for its use in medical rehabilitation applications or serious games, but it is it can also be considered in ludic VR applications. 4. The software is plain and simple to use, and integrates easily in all platforms with standard communications protocols. 5. The cost of all electromechanical parts used in the device have been carefully analyzed in order to fit the final cost. In addition, hardware architecture is defined in such a way to easily incorporate extensions of new wearable sensors (EMG, EEG, Heart Rate, etc.). The rest of the paper is organized as follows: first, the materials and methods of the system are described, along with the details of its HCI in Section 2.