Chain saw

A chain saw, comprising:

• a housing;
• a guiding plate installed on the housing and being movable forward and backward relatively to the housing;
• a chain arranged around the guiding plate;
• a power system installed on the housing and driving the chain;
• and
• a tensioning component comprising a knob, a driving member and a transmission assembly arranged between the knob and the driving member;
• wherein, when the chain is in a loose state, the knob is forced to rotate and drives the transmission assembly to rotate, the transmission assembly then drives the driving member to rotate, and the driving member drives the guiding plate to move to tension the chain;
• when the chain is in an extension state, the knob is forced to rotate, the driving member stays still, and a skidding inside the tensioning component is generated;
• wherein the transmission assembly comprises a releasing block, an elastic member and a gear set, the releasing block engages with the knob, and the elastic member is arranged between the knob and the releasing block, the releasing block comprises a plurality of inner teeth, and the gear set comprises a plurality of outer teeth;
• when the chain is in the loose state, the knob drives the releasing block to rotate, and the releasing block drives the gear set to rotate through the cooperation of the inner teeth and the outer teeth, then the gear set drives the driving member to rotate;
• when the chain is in the extension state, the skidding inside the tensioning component is generated between the inner teeth and the outer teeth;
• and
• wherein the gear set comprises a sun gear pivot mounted on the knob and at least one planetary gear pivot mounted on the driving member, the knob is arranged outside the gear set, and an inner ring gear is arranged on an inner wall of the knob for matching with the at least one planetary gear.