Lvdt-built-in linear motor

An LVDT-built-in linear motor comprising:

• an exterior member;
• and
• an inner yoke disposed at a center part of an inner space of the exterior member, wherein in a space formed between the exterior member and the inner yoke, a permanent magnet fixed inside the exterior member, a bobbin made of a non-magnetic material and disposed on an inner side of the permanent magnet and an outer side of the inner yoke such that the bobbin is capable of linearly moving, and a coil wound around an outer circumference of the bobbin are arranged, and the linear motor drives a drive unit of a hydraulic device so as to cause the drive unit to reciprocate via the bobbin that is linearly moved together with the coil by control of energization to the coil,
• the inner space of the exterior member, the inner yoke, the bobbin, and the coil each have a substantially cylindrical shape and are arranged coaxially with each other,
• the permanent magnet is divided into two in a longitudinal direction of the permanent magnet, and one of which is a first magnet disposed on a proximal side of the hydraulic device and the other of which is a second magnet disposed on a distal side of the hydraulic device,
• the coil includes a first coil and a second coil that are spaced apart from each other,
• the first coil and the second coil are formed by winding coil wires in opposite directions, and the first magnet and the second magnet have magnetic pole directions opposite to each other in a radial direction,
• the bobbin includes a cylindrical body having an outer circumference around which the first coil and the second coil are wound, and a protrusion that extends in a substantially cone shape from an edge of the cylindrical body and transmits the linear motion to the drive unit of the hydraulic device at a tip portion of the protrusion,
• an LVDT case member in which solenoid coils constituting a linear variable differential transformer (LVDT) are built in a region in front of an end of the first magnet closer to the hydraulic device is projected at an end of the inner yoke on a hydraulic device side,
• a core of the linear variable differential transformer that linearly moves inside the solenoid coils built in the LVDT case member as the bobbin linearly moves is coupled to the protrusion of the bobbin, and
• the linear motor further comprises a magnetic ring made of a soft magnetic material and disposed in contact with the end of the first magnet closer to the hydraulic device.