# Development and Validation of a System for Game Control Based on a Force Plate
## 2 System Description  
The game control system based on a force plate is shown in Figure 1, with its goal being to control games by utilizing changes in the player's CoP and acceleration of the CoM along the \(z\) axis. Additionally, this system can also be used to analyze human balance and postural stability without any additional modifications. The system shown in Figure 1 consists of a force plate, an electronic board used for measuring and PC communication, and a PC application for data acquisition, system calibration, and game control.  
Figure 1: System for game control based on a force plate.  
The force plate contains four load cells which are used to calculate the position of the CoP and the acceleration of the CoM of the human body along the \(z\) axis. The electronic board for measuring and PC communication conducts the force measurement procedure with the help of the load cells and then processes the data and sends the data in the form of a data frame every 100 ms to the PC via USB communication. The PC application for data acquisition, system calibration, and game control receives the data frame, which contains information about the forces measured at the load cells, presents the data, logs it into a textual file for later analysis, conducts the system calibration individually for each player, and finally simulates the keyboard key press or mouse cursor movement or left click, all with the goal of controlling games.  
The game control system is used as follows. The player stands on the force plate with both feet so that they do not step out of the force plate frame. After that, the system calibration is carried out in three steps. In the first step, the player stands still on the force plate so as to measure the initial position of the CoP, as well as the player's mass. By measuring these parameters, the system adapts to the player's local coordinate system so that they can control the game. In the next step, the player moves his or her CoM to establish the boundaries within which the CoP can move. With this step, scaling parameters are set for the shift in the position of the CoP within the given ranges; that is, the work plane of the player is defined. In the third step, the player's CoM acceleration along the \(z\) axis is measured by performing impulse half squats. This is a state where the human body generates a ground reaction force through muscles along the \(z\) axis without performing a jumping motion. By measuring the acceleration of the player's CoM along the \(z\) axis, a threshold is determined at which pressing the SPACE keyboard key or a left mouse button click will be simulated.  
After the system is calibrated, it is ready to be used to control games. During the game, the PC application calculates the position of the human body's CoP and acceleration of the CoM along the z axis. Based on the calculated values, it simulates pressing the UP, DOWN, LEFT, RIGHT, and SPACE keyboard keys or movements of the cursor and clicking the left mouse button. This is what enables controlling games using the player's CoP and the acceleration of the player's CoM along the \(z\) axis. The developed and constructed prototype of the system for game control based on a force plate with a player is shown in Figure 2. The image shows all the described parts of the system.  
Figure 2: Prototype of the system for game control based on a force plate.