2019 IEEE 25 th International Symposium for Design and Technology in Electronic Packaging ( SIITME) 1 23-26 Oct 2019, Cluj-Napoca, Romania A System for Measurement of the Asymmetry between Left and Right Shoulders Boris I. Evstatiev Faculty of Electrical Engineering, Electronics and Automation University of Ruse Angel Kanchev Ruse 7017, Bulgaria bevstatiev@uni-ruse.bg Iskra S. Ilieva, Asen T. Asenov Faculty of Transport University of Ruse Angel Kanchev Ruse 7017, Bulgaria {isilieva, asasenov}@uni-ruse.bg Emil H. Yankov Faculty of Mechanical and Manufacturing Engineering Faculty of Mechanical and Manufacturing Engineering eyankov@uni-ruse.bg Abstract—The study presents the development of a system for measurement of the asymmetry between the human shoulders. Such measurements are necessary in order to diagnose potential muscular imbalance and when possible, take corrective actions in the form of daily exercises. The system is based on two infrared proximity sensors, installed above the shoulders of the investigated human shoulders. A calibration procedure of the sensors and a following calibration model selection reduced the absolute error for the shoulders difference below 1.49 mm. Yet, if the measurement distance is kept within the range (40…110) mm, the accuracy is below 1 mm. The experiments also showed that the calibration is individual for each reflection surface, which should be considered during experimental measurements. Keywords—measuring system, muscular imbalance, infrared sensors I. INTRODUCTION The human body often has left-right asymmetry. This is caused by differences between the two sides such as muscular imbalance, structural issues, or even by imbalance somewhere else in the body. If corrective actions are not taken, it could lead to bone problems, which start as early as in the kinder garden. Nowadays 12% of students have already developed scoliosis, while 63% of children and 50% of people in Bulgaria have spinal distortion [1]. The muscular balance is commonly disturbed by bad habits, related to the body posture, though the imbalance could be reduced through properly selected physical exercise [2]. There are different methods to diagnose the muscular imbalance, and one of them is the difference in the levels between the left and right shoulders. To achieve this, a measurement system should be created, based on a microcontroller and sensors [3]. Several approaches could be identified when measuring height. Jeges et al. (2008) used a camera and a carpet pattern as a calibrator [4]. Another approach for height detection of vehicles has been applied by Liu and He (2018), which is also applicable for humans [5]. In the study, laser transmitting and receiving terminals were installed at different heights. For this situation, the accuracy depends almost entirely on the steps between the laser transmitter/receiver couples. Another approach was presented in Valtonen et al. (2011) where the human body was modeled a capacitor in order to obtain its height [6]. The obtained measurement accuracy was 5.2 cm though. Okuda et al (2005) used a pyroelectric sensor to detect human height and position [7]. The average accuracy was about 91% and depended on the height and movement speed. In another study, Rouveure et al (2014) used a radar system to measure the distance from soil of a hydraulic excavator’s cutting head [8]. Another option for height measurement are the ultrasonic sensors. Sharma et al (2016) presented the use of an acoustic sensor to measure the height of corn, though the measurement accuracy was several cm [9]. In another study, Nguyen et al (2017) presented a portable height measurement system, also based on ultrasonic sensors [10]. The results showed the error depends on the actual height of the object. Shahdib et al (2013) presented an obstacle detection and size measurement system based on a combination of camera and ultrasonic sensor [11]. The obtained relative error varied between 3% and 21%, depending on the size of the object. Unlike previous studies, our goal is to measure the height difference between the left and right shoulder. Since the measuring system is developed with scientific purpose our goal is to achieve accuracy as high as 1 mm. This paper will present the design and development of a measurement system for evaluation of the asymmetry between the left and right shoulders of a human body. II. MATERIALS AND METHODS A. The Measurement System For the implementation of the measuring system, we have selected the ST VL6180X infrared proximity sensors with measuring distance 1 cm - 20 cm, resolution 1 mm and supply voltage 2.7V – 5.5V. According to the specification, their accuracy depends slightly on the reflectance ratio of the measured surface, which should be considered. The two sensors are connected through an I2C interface to an Arduino Mega 2560 microcontroller as shown in Fig. 1. The communication is implemented through the SDA and SCL ports of the devices as well as the GPIO0 port of the sensors, necessary for assigning their unique addresses. A simplified scheme of the measuring system is presented in Fig. 2. The sensors are positioned above the shoulders and their horizontal and vertical position can be regulated, depending on the person’s width and height. The system acquires the sensor’s readings and assesses the asymmetry  between the shoulders according to: