FIG. 19 illustrates a conventional linear motor Tubular outer yoke 201 houses tubular inner yoke 203 having coil 202. Permanent magnet 204 is disposed between outer yoke 201 and inner yoke 203. Magnet 204 vibrates following the magnetic flux generated by inner yoke 203, so that a vibrator—fixing magnet 204—reciprocates.
The linear motor discussed above; however, has the following problems:
(1) The permanent magnet is fixed to the vibrator on its outer yoke side. The vibrator is thus positioned between the inner yoke having the coil and the permanent magnet. Thus a space between the inner yoke and the magnet becomes too wide. As a result, magnetic-flux-path incurs some loss. Further, the magnetic flux generated by the inner yoke changes greatly, so that eddy current is produced at a vibrator facing the inner yoke.
(2) The vibrator supporting the permanent magnet is non-magnetic body, thus when the vibrator is placed between the magnet and the yoke, non-magnetic-section other than the space is produced. This structure allows the non-magnetic-section to interfere with magnetic-flux for generating vibration, thus the vibrator cannot vibrate efficiently.
(3) Both the inner and outer yokes are formed by laminating electromagnetic steel in the circumferential direction, therefore, manufacturing them is a cumbersome work.
The objective of the present invention is to provide a linear motor, where a space between the permanent magnet and the inner yoke is provided as narrow as possible, the production of eddy current is thus restrained, and the yoke is easy to manufacture.