The fixing assembly 940 may further include a flat washer 947 and a snap ring 949. The flat washer 947 may be disposed between the spring washer 945 and the inserting portion 941a of the plate spring 941 and can uniformly transmit the elasticity provided from the spring washer 945 to the inserting portion 941a.

The snap ring 949, which is a part that is fitted last on the bolt 943, can make the fixing assembly 940 maintain the assembled state in one module type without disassembling.

After the fixing assembly 940 is inserted in the fixing groove 930, a cover block 948 formed to correspond to the shape of the first fixing groove 931 can be inserted in the first fixing groove 931 and coupled to the fixing bracket (910, see FIG. 9). The cover block 948 can be fixed to the fixing bracket (910, see FIG. 9) by a fastener such as a bolt.

FIGS. 13A to 13D are views showing the sequence of coupling the connecting bracket 950 to the fixing bracket 910 according to another embodiment of the disclosure.