Brushless DC spindle motor startup control

• US 5,530,326 A
• Filed: 07/19/1993
• Issued: 06/25/1996
• Est. Priority Date: 07/19/1993
• Status: Expired due to Term

• Current Assignee: Maxtor Corporation (Seagate Technology Holdings Plc)
• Original Assignee: Quantum Corporation (Chi Ko Investment Co., Ltd.)
• Inventors: Swiger, Daniel E., Galvin, John J.
• Primary Examiner(s): Sircus, Brian
• Application Number:
  US08/094,484
• Time in Patent Office: 1,072 Days
• Field of Search: 318/254, 318/138, 318/439, 318/696, 318/685
• US Class Current: 318/400.11
• CPC Class Codes: H02P 6/185 using inductance sensing, e.g. pulse excitation
• CPC Class Codes: H02P 6/22 in a selected direction of rotation

Abstract

Angular position of a polyphase brushless DC motor rotor is determined by the steps of generating a sequence of pulses with a programmed digital microcontroller, sequentially applying the pulses to selected ones of the plural windings or winding pairs, and sequentially measuring differential inductive coupling between the selected ones of the windings and selected others of the windings without rotating the rotor. Once angular position is determined, a multi-mode startup sequence is carried out to spin up the motor to a desired rotational velocity without any counter-rotation at startup.

Claims

1. A multi-mode control method for controlling startup of a polyphase brushless DC motor comprising the steps of:

determining with a programmed digital microcontroller an angular position of a rotor of the DC motor having a first plurality of permanent magnets and magnetic poles, and a stator having a core defining a second plurality of pole segments generally facing the magnetic poles and phase windings formed around the pole segments during a first operational mode,

generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with the programmed digital controller based upon determined angular position of the rotor,

applying the initial commutation sequence to the phase windings to start rotation of the rotor in a forward direction, without reverse rotation, with rotor angular position leading electrical phase angle of the initial commutation sequence,

monitoring back-EMF induced in the phase windings to determine rotor angular position relative to the initial commutation sequence to determine a cross-over between rotor angular position and electrical phase angle of the initial commutation sequence during a second operational mode, and

generating a back-EMF commutation sequence with a motor controller from monitored back-EMF and commutating the motor with the back-EMF commutation sequence following the cross-over, during a third operational mode.

2. The multi-mode control method set forth in claim 1 wherein the programmed digital microcontroller qualifies the back-EMF commutation sequence during an initial portion of the third operational mode, until a predetermined rotational velocity is reached, whereupon the programmed digital microcontroller ceases to qualify the commutation control to the motor controller.

3. The multi-mode control method set forth in claim 1 wherein the step of determining the angular position of the rotor is carried out by the steps of generating a sequence of pulses with the programmed digital microcontroller, sequentially applying the pulses to selected ones of the windings and sequentially measuring differential inductive coupling between the selected ones of the windings and selected others of the windings without rotating the rotor.

4. The multi-mode control method set forth in claim 1 wherein the step of determining the angular position of the rotor by the steps of:

sequentially applying with the programmed digital microcontroller a driving current pulse at a power level below a level overcoming starting friction of the rotor successively and bidirectionally to each of the windings as a driven winding during a driving interval,

sequentially measuring with an analog to digital conversion means and the programmed digital microcontroller during a measuring interval immediately following the driving interval a response induced at a selected undriven winding of the core via inductive coupling of the stator core between the driven winding and the undriven winding, and

determining with the programmed digital microcontroller the position of the rotor relative to the stator by identifying a driven winding and a current direction manifesting a lowest amplitude response in the selected undriven winding.

5. A multi-mode control method for controlling startup of a polyphase brushless DC motor comprising the steps of:

determining with a programmed digital microcontroller the angular position of a rotor of the DC motor having a first plurality of permanent magnets and magnetic poles, and a stator having a core defining a second plurality of pole segments during a first operational mode by the steps of;

sequentially applying with the programmed digital microcontroller a driving current pulse at a power level below a level overcoming starting friction of the rotor successively and bidirectionally to each of the windings as a driven winding during a driving interval,

sequentially measuring with an anolog-to-digital conversion means and the programmed digital microcontroller during a measuring interval immediately following the driving interval a response induced at a selected undriven winding of the core via inductive coupling of the stator core between the driven winding and the undriven winding, and

determining with the programmed digital microcontroller the position of the rotor relative to the stator by identifying a driven winding and a current direction manifesting a lowest amplitude response in the selected undriven winding,

generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with the programmed digital controller based upon determined angular position of the rotor in order to start rotation of the rotor in a forward direction without reverse rotation,

applying the initial commutation sequence to the phase windings,

monitoring back-EMF induced in the phase windings to determine rotor angular position relative to the initial commutation sequence to determine a cross-over between rotor angular position and electrical phase angle of the initial commutation sequence, during a second operational mode,

generating a back-EMF commutation sequence with a motor controller from monitored back-EMF following the cross-over, including qualifying the back-EMF commutation sequence with the programmed digital microcontroller during a third operational mode until a predetermined rotational velocity is reached, and

generating a back-EMF commutation sequence with the motor controller from monitored back-EMF without qualification by the programmed digital microcontroller after the predetermined rotational velocity is reached, during a forth operational mode.

6. A method for determining the angular position of a rotor of a polyphase brushless DC motor for enabling startup in a forward direction of rotation without any reverse rotation, the motor including a rotor having a plurality of permanent magnets and magnetic poles and a stator having a core defining a different plurality of pole segments generally facing the magnetic poles and phase windings around the pole segments, the core becoming nearly saturated by the presence of magnetic fields emanating from the magnetic poles in the absence of any driving currents in the windings, comprising the steps of:

sequentially applying a driving current pulse at a power level below a level overcoming starting friction of the rotor successively and bidirectionally to each of the windings as a driven winding during a driving interval thereby selectively to increase or decrease the level of magnetic saturation in the core,

sequentially measuring during a measuring interval immediately following the driving interval a response induced at a selected undriven winding of the core via inductive coupling of the stator core between the driven winding and the undriven winding, the response being an inverse function of saturation level of the core, and

determining rotor position relative to the stator by identifying a driven winding and a current direction manifesting a lowest amplitude response in the selected undriven winding.

7. The method set forth in claim 6 wherein the step of sequentially measuring comprises the steps of digitally selecting the undriven winding, and coupling an analog to digital conversion means to the undriven winding during the measuring interval, and converting the response induced in the undriven winding into a digital value.

8. The method set forth in claim 7 wherein the determining step comprises recording each of the digital values in memory locations, and identifying the recorded digital value having the lowest absolute magnitude.

9. A control method for controlling startup of a polyphase brushless DC motor having a movable rotor and phase windings, the method comprising the steps of generating an initial commutation sequence characterized by a non-linear commutation ramp for the phase windings of the DC motor with a programmed digital controller and a motor controller in order to start rotation of the rotor in a forward direction with rotor angular position leading electrical phase angle of the initial commutation sequence, applying the initial commutation sequence to the phase windings, monitoring back-EMF induced in the phase windings to determine rotor phase lead to determine convergence of rotor phase with an electrical phase angle of the commutation sequence and thereupon generating a back-EMF commutation sequence with the motor controller from monitored back-EMF and commutating the motor with the back-EMF commutation sequence following convergence.