In the article "Calculation and Evaluation of AGV Suspension and Braking Torque," we introduced methods for calculating the inertial force of an AGV cart, the braking torque, and the required normal force on the steering wheels. Today, we will introduce how to calculate and evaluate the braking distance of an AGV during emergency braking.
Since our evaluation is based on the distance the AGV moves after the emergency stop button is pressed-including the distance covered during the braking system's response (while the brakes are being applied) and the subsequent distance due to inertia after the brakes are fully engaged-we can analyze the process in two stages: the reaction distance and the sliding distance.
Below, we discuss the reaction distance. The reaction distance is defined as the displacement of the AGV cart from the moment the emergency stop button is pressed until the control system processes the signal and the brakes are completely applied. The key parameters are the operating speed at the time of the emergency stop and the response time of the entire braking system. The figure below shows the operating time-sequence parameters of a certain brand's brake. According to the model used on the steering wheels, one should refer to the corresponding table to determine the delay time during brake application.
If the brake is powered by an intermediate relay, an additional delay of several tens of milliseconds may be added (or one may refer to the intermediate relay's manual for the actual delay time). If the drive controller is used directly, this delay can be ignored. For the sake of evaluation, we assume the braking system's response time is 100 ms (i.e., 0.1 s) and that the AGV cart is executing an emergency stop at 1 m/s. Thus, the reaction distance is calculated as follows:
Reaction Distance = vt = 1 m/s * 0.1 s = 0.1 m
After the brakes are fully engaged, the AGV cart continues to move due to inertia. The sliding distance is related to the friction coefficient between the wheels and the ground and the deceleration. Assuming a comprehensive friction coefficient of 0.2 between the wheels and the ground, the sliding distance is calculated as:
Sliding Distance = v²/(2μg) = 11/(20.2*10) = 0.25 m
Therefore, the total braking distance is:
Braking Distance = Reaction Distance + Sliding Distance = 0.1 m + 0.25 m = 0.35 m
Summary:
This article introduces the method for calculating the braking distance of an AGV. The calculation shows that the reaction distance during emergency braking is directly proportional to the speed and the response time of the braking system, while the sliding distance is directly related to the initial speed and inversely related to the friction coefficient.
