Table 1.

List of notations.

Notation	Definition
$D_i$	The i-th charging location
$Q(D_i,D_j)$	Action value of the action moving from $D_i$ to $D_j$
$r\left(D_i\right)$	Reward obtained after the MC moves to $D_i$
$\alpha$	The learning rate of the Q-learning algorithm
$\gamma$	The discount factor of the Q-learning algorithm
$E_{th}$	The threshold for sending a charging request
$E_{sf}$	The safe charging level
$\theta$	The safe energy factor
$E_{max}$	The maximum energy capacity of the sensors
$p_j^i$	The per second energy that a sensor $S_j$ is charged when the MC stays at $D_i$
$e_j$	Energy consumption rate of sensor $S_j$
$E_j$	Remaining energy of sensor $S_j$
${\mathcal{T}}_i$	The optimal charging time at $D_i$
$L_r,E_{min}$	Fuzzy input variables
$w_j$	The priority index of $S_j$
${\xi }_j$	The energy severity index of $S_j$, ${\xi }_j=\frac{e_j}{E_j}$.