a base, comprising a bottom plate and a first side plate arranged on one side of the bottom plate, wherein the bottom plate and the first side plate are enclosed to form a first accommodating chamber; a ratchet part is arranged at one end of the first side plate away from the bottom plate; the ratchet part is annularly arranged on the first side plate and is located in the first accommodating chamber; the first side plate is provided with a first threading hole and a second threading hole which are configured to thread a cord; the second threading hole is communicated to the first accommodating chamber;

a reel, provided with a winding region configured to store the cord, wherein the reel is arranged in the first accommodating chamber and is rotatably connected to the base;

a pawl disk, arranged in the first accommodating chamber and connected to the reel, wherein the pawl disk comprises a pawl arm; the pawl arm moves along the ratchet part to control a length of retraction and deployment of the cord; when the pawl arm resists against the ratchet part, the pawl disk and the reel are stationary relative to the base; when the pawl arm is separated from the ratchet part, the pawl disk and the reel rotate relative to the base;

a knob, arranged on one side of the base facing the first accommodating chamber, rotatably connected to the base, and capable of being turned in a preset direction, wherein the knob comprises a top plate and a first driving member arranged on one side of the top plate facing the base; the first driving member drives the pawl arm to be separated from the ratchet part and drives the reel to rotate relative to the base, so as to retract or deploy the cord into or from the winding region; and

a control member, arranged between the reel and the base, wherein the reel is rotatably connected to the base through the control member; and when the knob is turned in a first direction, the control member moves in a direction from the bottom plate to the top plate; and when the knob is turned in a second direction, the control member moves in a direction from the top plate to the bottom plate, movement of the control member to the bottom plate or the top plate is capable of preventing the knob from further rotation, so as to limit a rotation distance of the reel and control the length of the cord for retraction or deployment.