REDUCED-VIBRATION STEPPER MOTOR

• US 20170149322A1
• Filed: 11/24/2015
• Published: 05/25/2017
• Est. Priority Date: 11/24/2015
• Status: Active Grant

• Current Assignee: LIN Engineering, Inc.
• Original Assignee: Lin Engineering Co.
• Inventors: Nguyen, Harlan H., Lin, Ted T.
• Granted Patent: US 9,966,829 B2
• Time in Patent Office: Days
• CPC Class Codes: H02K 37/22 Damping units

Abstract

A stepper motor has a stator winding assembly with a permanent ring magnet located radially outside of electromagnetic windings for the stator poles. The permanent ring magnet remotely magnetizes a rotor seated by bearings on an axial shaft so as to rotate within the stator winding assembly, thereby freeing up space within the rotor for an internal damper. The rotor has a cylindrical damping weight enclosed within, but not fixed to, the rotor. The weight ideally has a rotational moment of inertia that substantially matches that of the rotor. The weight is elastically coupled to the rotor by a viscous material contained in the rotor and filling the space between the weight and the rotor and between the weight and the axial shaft. The viscosity of this material is selected such that motion of the weight is delayed, preferably so as to be substantially 180° out-of-phase with, but at the same frequency as, the stepping rotation of the rotor. The weight thereby serves as a counterweight to the rotor so as to cancel vibrations generated by stepping of the rotor.

Claims

1. A reduced-vibration step motor, comprising:

a stator winding assembly including a stator with a set of stator poles wound with coils that can be driven in a series of phases so as to magnetically interact with a rotor, the stator poles having sets of stator teeth that are selectively magnetized by energizing of the stator coils, the stator also having a permanent ring magnet located radially outside of the coils and sandwiched between outer portions of two stator stack elements of the stator; and

a rotor with a plurality of rotor teeth, the rotor fitting within the stator winding assembly and seated by bearings on an axial shaft so as to rotate Within the stator winding assembly, the permanent ring magnet in the stator producing magnetic flux passing axially through a ring interior to remotely magnetize the rotor and its rotor teeth, such that magnetic flux in an air gap between rotor and stator teeth is dominated by the flux generated by Ampere-turns of energized stator coils with reduced flux interactions from non-energized poles, the rotor being characterized by having a viscous mechanical damper internal thereto.

2. A motor as in claim 1, wherein the viscous mechanical damper comprises a weight enclosed within, but not fixed to, the rotor and mechanically coupled thereto by a viscous material such that motion of the weight is substantially out-of-phase with, but at the same frequency as, the stepping rotation of the rotor.

3. A motor as in claim 2, wherein the weight comprises a cylindrical body having a rotational moment of inertia that substantially matches that of the rotor.

4. A motor as in claim 2, wherein the viscous material is contained within the rotor and fills space between the weight and the rotor and between the weight and the axial shaft, the viscous material providing an elastic coupling of the weight to the rotor with a damping character having been selected to obtain the substantially out-of-phase motion of the weight to cancel vibrations of the rotor.

5. A reduced-vibration step motor, comprising:

a stator winding assembly including a stator with a set of stator poles wound with coils that can be driven in a series of phases so as to magnetically interact with a rotor, the stator poles having sets of stator teeth that are selectively magnetized by energizing of the stator coils, the stator also having a permanent ring magnet located radially outside of the coils and sandwiched between outer portions of two stator stack elements of the stator; and

a rotor with a plurality of rotor teeth, the rotor fitting within the stator winding assembly and seated by bearings on an axial shaft so as to rotate within the stator winding assembly, the permanent ring magnet in the stator producing magnetic flux passing axially through a ring interior to remotely magnetize the rotor and its rotor teeth, such that magnetic flux in an air gap between rotor and stator teeth is dominated by the flux generated by Ampere-turns of energized stator coils with reduced flux interactions from non-energized poles, the rotor being characterized by having a cylindrical weight enclosed within, but not fixed to, the rotor, the weight having a rotational moment of inertia that substantially matches that of the rotor, the weight further being elastically coupled to the rotor by a viscous material contained in the rotor and filling the space between the weight and the rotor and between the weight and the axial shaft, the viscous material having a viscosity selected such that motion of the weight is substantially out-of-phase with, but at the same frequency as, the stepping rotation of the rotor so as to cancel vibrations of the rotor.