Cost-saving, small-sized motor with improved stability over wide speed range

A motor comprising:

• (a) a shaft;
• (b) a rotor member having a symmetric shape relative to said shaft, said rotor member being fixed to said shaft;
• (c) an annular magnet assembly fixed to said rotor member with said shaft passed through said magnet assembly at a center thereof, said magnet assembly including K driving magnetized elements, each of equal dimension, aligned at a perimeter of said magnet assembly about said shaft such that each has a pole opposite the pole of neighboring driving magnetized elements, where K is an even number larger than two;
• and
• (d) an armature having a plurality of armature coils which are opposed to the driving magnetized elements at a predetermined distance such that said armature reacts with the driving magnetized elements to cause said rotor member to rotate,
• said magnet assembly further comprising:
• (1) M first sensed magnetized elements provided in each of said driving magnetized elements such that said first sensed magnetized elements each have a pole opposite the pole of a corresponding driving magnetized element, where M is a natural number and each of said first sensed magnetized elements is 1/(2M+1) in length with respect to each of said driving magnetized elements in a circumferential direction of said magnet assembly;
• and
• (2) second sensed magnetized elements provided in two adjacent ones of said driving magnetized elements such that each has a pole opposite the pole of the corresponding driving magnetized element, said second sensed magnetized elements being radially displaced from the corresponding first sensed magnetized element, and
• said motor further comprising magnetic field sensing means disposed on a surface of said armature opposed to said magnet assembly for sensing alternating magnetic fields as said rotor member rotates.

A combination of an annular magnet assembly and a magnetic field sensor assembly for use in measuring a rotation speed of a rotating member having a rotor member, the magnet assembly being fixed to the rotor member and said magnet assembly comprising:

• K driving magnetized elements, each of equal dimension, aligned at a perimeter of said magnet assembly about said shaft such that each has a pole opposite the pole of the neighboring ones, where K is an even number larger than two,;
• M first sensed magnetized elements provided in each of said driving magnetized elements such that said first sensed magnetized elements each have a pole opposite the pole of a corresponding driving magnetized element, where M is a natural number and each of said first sensed magnetized elements is 1/(2M+1) in length with respect to each of said driving magnetized elements in a circumferential direction of said magnet assembly;
• and
• second sensed magnetized elements provided in two adjacent ones of said driving magnetized elements such that each has a pole opposite the pole of the corresponding driving magnetized element, said second sensed magnetized elements being radially displaced from the corresponding first sensed magnetized element,
• said magnetic field sensor assembly being opposed to the magnet assembly for sensing alternating magnetic fields as the rotor member rotates.