# A Neuro-Prosthetic Device for Substituting Sensory Functions during Stance Phase of the Gait
## 1 Introduction  
A Background on Functional Electrical Stimulation Devices and Application of Sensors in Gait Event Detection and Control  
Micro-electronics have recently emerged as the central part of many devices and lab equipment in biology and neuroscience [1; 2; 3]. One application is in electrical stimulation of nerve tissues and body organs which is important in neuroscience both in understanding the mechanisms of neuronal activity and animal behavior and as a tool for treatment of central and peripheral nervous system disease [4]. Functional Electrical Stimulation (FES) is a technique that applies electrical charge to muscles and organs for rehabilitation and achievement of dynamic movements [5; 6; 7]. Neural prostheses to deliver FES may have an analytical and stimulation core to gather data from sensors and actively control the electrical charge delivered to muscles using electrodes [8]. Timing control for stimulation is necessary and important for these devices and, therefore, the sensing core of the device must gather information about the gait phases [9; 10; 11]. Different FES systems utilize different sensors and different timing control methods depending on the moving function the device aims to assist or replace and the remaining abilities of patient after neural injuries. Usually, a combination of different sensors is used in an FES system to gather gait data in real time. Accelerometers, gyroscopes, and force-sensitive resistors are common sensors that are utilized in FES systems. A common application of FES is in drop-foot stimulator devices where the peroneal nerve and tibialis anterior muscle are stimulated during the swing phase of the gait to raise the toes and prevent falling [12; 13]. The force-sensitive resistor is the most common sensor used in such stimulators to control stimulation timing. This sensor is placed inside the shoe and under the heel. When patient lifts the heel from the ground, the force is removed from the sensor or heel switch. This indicates the start of swing phase and stimulation is initiated. Once the force is reapplied on the sensor, stimulation is terminated. Some researchers developed advanced stimulators for this purpose to detect more gait events and assist patients suffering from dropped foot. [PERSON] et al. [14] invented a gait neuro-prosthesis to help these patients using FES. They selected Arduino MCU as their computational modulus to obtain data from Inertial Measurement Units (IMUs) and force-sensitive resistors and then calculate and control the actuation command to target muscles. For some FES systems with simple application of stimulation and gait detection methods, a smaller number of sensors are used. [PERSON] et al. [15] utilized a single gyroscope attached on the shank of the human patient to measure shank angular velocity and detect stance/swing phase of the foot. For complicated systems with FES applications, more accurate gait event detection is needed, which has encouraged extensive research in this field to propose different methods and algorithms. As an example, [PERSON] et al. [16] designed a real-time system using two inertial measurement units to detect seven phases of the gait with very high reliability. In this study, we develop a wearable neuro-prosthetic device to replace sensory functions of patients that suffer spinal cord injuries. We first design this device for dogs that we selected as our animal subject. We design an advance sensing core for this device to determine and calculate the stimulation command based on three timing controls. The first timing control is based on the hip orientation of the patient. The second is based on stance/swing phase gait detection, and the third is based on gait abnormalities during swing phase. In this paper, we omit discussion of the third timing control since it is the subject of another study, which will be reported elsewhere.