Force sensor and motor-driven parking brake apparatus using the same

A force sensor comprising:

• a first member to which a magnet is fixed by a torsion spring such that the magnet is rotatable and movable together with the first member;
• a second member to which an electrical element is fixed, the electrical element outputting an output voltage that varies in accordance with relative displacement of the electrical element with respect to the magnet;
• a main spring interposed between the first member and the second member and elastically deforming in accordance with force produced between the first member and the second member along a direction of reciprocation of the first member with respect to the second member;
• and
• a sub spring for imparting a preload such that, in a state in which the amount of elastic deformation of the main spring is substantially zero, no clearance along the direction of reciprocation is formed between the first member and one end portion of the main spring and no clearance along the direction of reciprocation is formed between the second member and the other end portion of the main spring;
• the main spring and sub spring are arranged such that as the amount of elastic deformation of the main spring increases, the amount of elastic deformation of the sub spring decreases.