Electromagnetic force balance

An electromagnetic force balance comprising a lever portion extending forwardly and backwardly from a fulcrum, a coil to be mounted at a backward side from the fulcrum of the lever member, and a magnetic circuit for developing magnetic field to act on the coil, wherein a force to act on a force point of the lever portion is compensated by supplying a current to the coil, characterized in that:

• the coil is a flat coil comprising upper and lower winding portions that are parallel with the extending direction of the lever portion and extending along a vertical plane parallel with the extending direction of the lever portion;
• and
• the magnetic circuit comprises:
• a plate-shaped upper permanent magnet facing the upper winding portion of the flat coil and magnetized in the direction perpendicular to the vertical plane;
• a plate-shaped lower permanent magnet facing the lower winding portion of the flat coil and magnetized in the opposite direction to the upper permanent magnet;
• a plate-shaped upper opposing yoke member facing the upper permanent magnet by way of the upper winding portion of the flat coil and guiding the magnetic line of force in order to develop magnetic flux in an orientation orthogonal to the vertical plane;
• a plate-shaped lower opposing yoke member facing the lower permanent magnet by way of the lower winding portion of the flat coil and guiding the magnetic line of force in order to develop magnetic flux in the direction perpendicular to the vertical plane;
• a first lateral side yoke member raising vertically along the extending direction of the lever portion;
• a second lateral side yoke member raising in parallel with the first lateral side yoke member;
• a front side yoke member and a rear side yoke member each formed with a through-hole through which the lever portion extends;
• an upper yoke member for closing the upper side of a space surrounded by the first lateral side yoke member, the front side yoke member, the second lateral side yoke member and the rear side yoke member in four directions;
• a lower yoke member for closing the space;
• and
• wherein the first lateral side yoke member, the front side yoke member, the second lateral side yoke member, the rear side yoke member, the upper yoke member and the lower yoke member surround the flat coil;
• wherein the plate-shaped upper opposing yoke member and the lower opposing yoke member have the same area as the plate-shaped upper permanent magnet and the lower permanent magnet that oppose thereto by way of the flat coil;
• wherein the upper permanent magnet and the lower opposing yoke member are fixedly mounted on the inner surface of either one of the first lateral side yoke member and the second lateral side yoke member;
• and
• wherein the lower permanent magnet and the upper opposing yoke member are fixedly mounted on the inner surface of the other of the first lateral side yoke member and the second lateral side yoke member.