"Electronic replacement motor&αδπquot; (EC motor) and "stepping motor&qu¶£ot; belongs to the permanent magnet synchronous •≈motor, EC motor is usually"₽ designed for continuous drive t®δask, stepping motor design to perform as litα ₩tle as possible deviation of the rotation ÷←↓★Angle, and to keep the specified ste​©p position, they should have the largesΩ‍t possible to keep torque. This rγαequires that the size of the magnetic circuit ≥↔¶should be able to produce high groove torque↑☆≥σ (no current torque in phase) and the gro♦≥₽'ove torque overlaps with theδ‌ γ retention torque (current flows into>≈¥₩ the phase). Thus, torque fluctuations and torqu←&✘φe mutations are expected, like in EC motors, &λ↕✔where sinusoidal currents ☆ ←•are not used for stepping motors and in×   microstepping where the phase curren₽↔↕"ts can be opened and closed in small increments‍₹ in order to be in both holdingγ  positions, often used.
Stepping motors do not reqβ≥uire any permanent magnet, &✘so they do not have any slot torσ‍que, and these motors ("♣λ♠βswitched resistance motors") use v<≠ery low airgaps with a gap andσ® a width of 50 μ m is typical, which le≠λ♥ads to extremely high radial f♣¶₩σorces, resulting in severe deformation of the s✘÷tator and high noise. In the×✔ electronic commutation motor, the current a $∏‌pplied to each motor phase is di®→sconnected and connected through the e←β♣↓lectronic circuit. According to the mode≠ ↑ of these phase current over timeα∞, the radial force and tangential force are used ∏↕for the stator tooth and the force for th€β >e conductor in the motor phase, th©★≈e latter case is especially occurred on the✔¥ slot motor with an air gap winding. When  • the rectangular current mode cα↔  hanges over time, local rectangular f∞ε→orces are also generated over ti≠×↕ me, thus causing a sudden oscill↕← atory excitation at the stator, which ♦≤→stimulates the oscillations and thei"™εφr harmonics at the switching frequeλ ↔ncy (fundamental oscillation) of the c∑πurrent phase.
Under the ideal rectangular curre <nt and the ideal symmetric motor, the ↓±•torque remains constant over time, and if ther∏&£e is geometric asymmetry, phase↕←"↕ inductance and resistance differenceΩ₽‍ and electronic circuit di×≥δfference in reality, then the currπ£ent time interval or overlap wδ≈ill lead to each phase, whic ↑♣★h will lead to torque fluctuation×₽<♦ and stator vibration excitation. The resulti≤®₩ng noise is often called "commutationπγ≈ noise", its importance can not be unde✘₽restimated! Using an electronic controλ↓ l circuit that works with a sinusoidal current mo ≤"≈de causes reduced motor efficiency, but it doe♠©÷∏s eliminate or at least substant∞♠♠ially reduce this type of noise.
The mechanical vibration of small motor sl≠λ♠δiding bearing is the result of intermit♦δtent mechanical contact between the sh♠<πaft and the bearing surface. Wh'→en the lubricating oil film carries the load ar→∞<ound the shaft and the bearing, there‍☆≈ε is no such contact and any noise.∑λ© However, at startup, when the radial forc ♥±♠e on the bearing is too large (belt drive, ge©§≥ar, air gap field), when the λ>₽shaft and / or bearing sleeve are not>¶ round or bent, if there is÷‌  no enough porosity on the sintered bβ ₽earing surface, if the shaf§♠™≈t running surface is too smooth, or if there  ♣is not enough lubricant in the bearing (×✔mixed friction). The result is the vibration at tφ§÷he peak roughness of the bearing s•≤↑<urface, which depends on the ela★γsticity of the shaft or bearing, at many frequen®‍cies in the audible range (frequency bands↔& in the spectrum). The frequency of t≥←£he rotation and its multiple ≥♣are particularly pronounced. The amplitude of hig€↔↑h-frequency vibrations is often simply✔≥ modulated, making frictional noise particular≤☆Ωly a nuisance. As the lack of lu£ ↕≤bricating oil increases, mechanical contact inλ‍∞¥creases, causing mechanical friction,γ≤>± and wear increases sharply,‍↓ which happens