Table 1 The main notations defined in our model

N

The total number of disassembly tasks for a product

i, j

Task indices, i, j = 1, 2, …, N

F_seq

Set of feasible disassembly sequences

k

Position indices in the disassembly sequence (The positions in the disassembly sequence correspond to the tasks to be processed one by one)

d_ij

Penalty cost of direction change for performing tasks i and j

d_k,k+1

Penalty cost of direction change for performing two tasks at the kth and (k+1)th position

C_d

Penalty costs of direction change for the disassembly sequence

t_ij

Penalty cost of tool change for performing tasks i and j

t_k,k+1

Penalty cost of tool change for performing two tasks at the kth and (k+1)th position

C_t

Penalty costs of tool change for the disassembly sequence

K_i

Position of task i in the sequence

TC

The total penalty costs of performing the disassembly sequence

Decision variables:

seq

Index for disassembly sequence

x_k

The task at the kth position