Open-loop step motor control system

• US 6,016,044 A
• Filed: 09/11/1995
• Issued: 01/18/2000
• Est. Priority Date: 09/11/1995
• Status: Expired due to Term

• Current Assignee: Carefusion 303 Incorporated (Becton, Dickinson & Co)
• Original Assignee: ALARIS Medical Systems, Inc. (Becton, Dickinson & Co)
• Inventors: Holdaway, Charles R.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US08/526,468
• Time in Patent Office: 1,590 Days
• Field of Search: 318/685, 318/696, 318/268-279, 318/369, 417/42, 417/43, 417/44.1, 417/44.2, 417/45, 417/410.1, 388/848, 388/853, 388/907.5
• US Class Current: 318/696
• CPC Class Codes: H02P 8/04 Arrangements for starting
• CPC Class Codes: H02P 8/22 Control of step size; Intermediate stepping, e.g. microstepping
• CPC Class Codes: H02P 8/24 Arrangements for stopping H02P8/32 takes precedence
• CPC Class Codes: H02P 8/32 Reducing overshoot or oscillation, e.g. damping

Abstract

A motor control system that reduces noise while reducing power requirements but providing sufficient torque. A one-phase-on drive mode modified to microstep between "one phase on" positions is used to accelerate the motor in a non-linear manner to a maximum speed. The microstep drive modes have a constant period, and the step rate of the motor is increased by decreasing the number of microsteps in succeeding steps of the motor. A modified full step waveform maintains the motor at the maximum speed, where the current to one winding of the step motor changes polarity within one motor step while the other remains approximately constant providing increased smoothness in the drive and reduced noise. The polarity changes in accordance with the inductance and the compliance voltage of the motor. A one-phase-on waveform modified to include microsteps between "one phase on" positions later decelerates the motor in a non-linear manner, and the motor stops in a detent position until another waveform of steps is delivered to the motor.

Claims

1. A control system for controlling the movement of a motor, the system comprising:

an energy source providing an electrical current; and

a controller that controls the energy source to provide an exponentially increasing winding current to the motor to begin movement of the motor,

wherein the controller applies energy to the motor in a "one phase on" drive mode modified to microstep between the "one phase on" positions during movement of the motor, and wherein the controller controls the motor to accelerate by decreasing the number of microsteps per motor step while maintaining a constant microstep period.

2. A control system for controlling the movement of a motor, the system comprising:

an energy source providing an electrical current; and

a controller that controls the energy source to provide an exponentially increasing winding current to the motor to begin movement of the motor,

wherein the controller removes energy from the motor in a "one phase on" drive mode modified to microstep between the "one phase on" positions during movement of the motor ending in a "one phase on" position for the last step of the motor before power is completely removed.

3. The control system of claim 2 wherein the controller controls the motor to decelerate by increasing the number of microsteps per motor step while maintaining a constant microstep period.

4. A control system for a step motor having at least two phases and a permanent magnet capable of defining a detent position, comprising:

an energy source;

a motor controller providing energy from the energy source to the step motor as a first mode drive signal to accelerate the step motor in an exponentially increasing manner to a constant speed, the first mode drive signal driving the step motor in a "one phase on" mode modified to microstep between "one phase on" positions of the motor, with a first selected number of microsteps per motor step, with the motor controller providing energy from the energy source to the step motor as a second mode drive signal to the step motor to maintain the constant speed, said second mode drive signal driving the step motor with a second selected number of microsteps per motor step, said second selected number being different from said first selected number.

5. The control system of claim 4 wherein the motor controller provides a third mode drive signal to decelerate the step motor from the constant speed in a non-linear decreasing manner to the detent position,

wherein the motor controller provides no drive signals to the motor after the motor stops in the detent position for a predetermined period of time.

6. The control system of claim 4, wherein

the second mode drive signal drives the step motor in a full step mode, whereby the second mode drive signal drives the step motor with one microstep per motor step, wherein one of at least two phases of the step motor changes polarity while the other phase remains at a constant value, and a step rate being selected such that the polarity change is performed in one motor step period whereby smooth motor field displacement is achieved.

7. The control system of claim 6, wherein the motor controller provides a third mode drive signal to decelerate the step motor from the constant speed in a non-linear manner to the detent position, wherein the third mode drive signal drives the step motor in a one-phase-on mode modified to microstep between "one phase on" positions.

8. The control system of claim 4, wherein each microstep has a constant period, and the second selected number of microsteps is smaller than the first selected number of microsteps,

whereby a motor step for the first mode drive signal is longer than a motor step for the second mode drive signal.

9. A pump for delivering fluid to a patient, the pump comprising:

a step motor having at least two phases and a permanent magnet capable of defining a detent position at rest; and

a motor controller providing drive signals to energize the phases of the step motor and control the step motor to move in a series of motor steps, the motor controller including a memory having a first look-up table having values for a first mode drive signal that accelerates the step motor in a rising non-linear manner to a constant speed, wherein each motor step for the first mode drive signal includes a first number of microsteps;

a second look-up table having values for a second mode drive signal that maintains the constant speed for the step motor, wherein each motor step for the second mode drive signal includes a second number of microsteps, said second number of microsteps being different from said first number of microsteps; and

a third look-up table having values for a third mode drive signal that decelerates the step motor from the constant speed in a non-linear manner to the detent position;

wherein the motor controller accesses the memory and the look up tables and applies multiple drive modes in accordance with the values of the look up tables to the motor to control the motor position; and

wherein the motor controller provides no drive signals to the motor after the motor stops in the detent position for a predetermined period of time.

10. The pump of claim 9, wherein

each microstep has a constant period;

and

each motor step for the second mode drive signal has a period equal to the microstep period;

whereby a motor step for the first mode drive signal is longer than a motor step for the second mode drive signal.

11. A method of controlling a step motor having at least two phases and a permanent magnet that defines a detent position at rest, comprising the steps of:

applying an exponentially increasing winding current to accelerate the step motor to a preselected motor speed;

maintaining the preselected speed for a first predetermined period of time; and

exponentially decreasing the winding current to decelerate the step motor from the preselected speed to the detent position after the first predetermined period of time, wherein the motor stops in the detent position for a second predetermined period of time,

wherein the acceleration step includes driving the step motor in a "one phase on" mode modified to microstep between the "one phase on" positions during movement of the motor; and

the maintaining step includes driving the step motor in a full step mode so that one of at least two phases of the step motor changes polarity while the other phase remains at a constant value, and the step rate being selected such that the polarity change is performed in one motor step period whereby smooth motor field displacement is achieved.

12. The method of claim 11 wherein the deceleration step includes the step of driving the step motor in a one-phase-on mode modified to microstep between the "one phase on" positions during movement of the motor.

13. The method of claim 11, wherein the step motor is driven in a series of motor steps, wherein:

each motor step for the acceleration step includes a plurality of microsteps, each microstep having a constant period;

each motor step for the maintaining step has a period equal to the microstep period;

whereby a motor step for the acceleration step is longer than a motor step for the maintaining step.

14. A method of controlling a step motor having at least two phases and a permanent magnet that defines a detent position at rest, comprising the steps of:

accelerating the step motor in a rising non-linear manner to a preselected motor speed;

maintaining the preselected speed for a first predetermined period of time; and

decelerating the step motor from the preselected speed in a non-linear manner to the detent position after the first predetermined period of time, wherein the motor controller provides no drive signals to the motor after the motor stops in the detent position for a second predetermined period of time,

wherein the step motor has a compliance voltage and an inductance, and each phase includes a winding having a winding current; and

the maintaining step includes driving the step motor in a full step mode, wherein one of the at least two phases of the step motor changes polarity as a function of time in accordance with the function;

##EQU2## where I_winding is the winding current, V_compliance is the compliance voltage of the controller, and L is the inductance of the motor winding;

wherein the step rate is selected such that the polarity change is performed in one motor step period whereby smooth motor field displacement is achieved.

15. A control system for controlling the movement of a motor, the system comprising:

an energy source; and

a controller that applies energy from the energy source to the motor, wherein the controller applies energy to the motor in a "one phase on" drive mode modified to microstep between the "one phase on" positions during movement of the motor, wherein the controller controls the motor by varying the number of microsteps per motor step while maintaining a constant microstep period,

wherein the controller controls the motor to accelerate by decreasing the number of microsteps per motor step while maintaining a constant microstep period.

16. A control system for controlling the movement of a motor, the system comprising:

an energy source; and

a controller that applies energy from the energy source to the motor, wherein the controller applies energy to the motor in a "one phase on" drive mode modified to microstep between the "one phase on" positions during movement of the motor, wherein the controller controls the motor by varying the number of microsteps per motor step while maintaining a constant microstep period,

wherein the controller removes energy from the motor in a "one phase on" drive mode modified to microstep between the "one phase on" positions during movement of the motor ending in a "one chase on" position for the last step of the motor before power is completely removed, and wherein the controller controls the motor to decelerate by increasing the number of microsteps per motor step while maintaining a constant microstep period.

17. A control system for controlling the movement of a motor, the system comprising:

an energy source; and

a controller that applies energy from the energy source to accelerate the motor through first and second motor steps, wherein the first motor step includes a first plurality of microsteps, and the second motor step includes a second plurality of microsteps, wherein the first plurality of microsteps is greater than the second plurality of microsteps,

wherein the controller applies energy from the energy source to accelerate the motor through a third motor step, wherein the third motor step includes a third plurality of microsteps

wherein the second plurality of microsteps is half as large as the first plurality of microsteps, and the third plurality of microsteps is half as large as the second plurality of microsteps.

18. The control system of claim 17, wherein the controller maintains a constant microstep period.

19. A control system for controlling the movement of a motor, the system comprising:

an energy source; and

a controller that applies energy from the energy source to drive the motor, wherein the controller has a compliance voltage and the step motor has an inductance and each phase includes a winding current; and

one of at least two phases of the step motor changes polarity as a function of time in accordance with the function;

##EQU3## where I_winding is the winding current, V_compliance is the compliance voltage of the controller, and L is the inductance of the motor winding;

wherein the step rate is selected such that the polarity change is performed in one motor step period whereby smooth motor is field displacement is achieved.

20. The control system of claim 19, wherein the step motor drives a pump mechanism for delivering fluid to a patient.

21. A method of controlling movement of a step motor that moves in a series of motor steps, comprising the steps of:

(a) controlling the step motor to move through a first accelerating motor step in a first plurality of microsteps;

(b) controlling the step motor to move through a second accelerating motor step in a second plurality of microsteps, the second motor step being subsequent to the first motor step, wherein the second plurality of microsteps is less than the first plurality of microsteps.

22. The method of claim 21, wherein steps (a) and (b) include maintaining a constant period for the microsteps.

23. The method of claim 21, wherein the second plurality of microsteps is equal to half of the first plurality of microsteps.

24. The method of claim 21, including the further step of;

(c) decreasing the number of microsteps per motor step for one or more acceleration motor steps subsequent to the second acceleration motor step.

25. The method of claim 24, wherein the second plurality of microsteps is equal to half of the first plurality of microsteps, and step (c) includes the step of reducing by half the number of microsteps per each subsequent acceleration motor step.

26. The method of claim 25, wherein the number of microsteps for each subsequent acceleration motor step is reduced by half until the number of microsteps per motor step equals one, and including the further step of:

(d) maintaining a constant step motor speed for a period of time after the number of microsteps equals one.

27. In an intravenous delivery system comprising a fluid supply, a fluid supply line, and a fluid pump having a fluid pump step motor operating on the fluid supply line to move fluid through the line, a method for delivering fluid to a patient, comprising the steps of:

accelerating the fluid pump step motor in a series of motor steps, wherein a first of said motor steps is divided into a first number of microsteps, and a second of said motor steps is divided into a second number of microsteps, wherein the first number of microsteps is twice the second number of microsteps.

28. In an intravenous delivery system comprising a fluid supply, a fluid supply line, and a fluid pump having a fluid pump step motor operating on the fluid supply line to move fluid through the line, a method for delivering fluid to a patient, comprising the steps of:

accelerating the fluid pump step motor in a series of motor steps, wherein a first of said motor steps is divided into a first number of microsteps, and a second of said motor steps is divided into a second number of microsteps, wherein the first number of microsteps is greater than the second number of microsteps,

wherein the series of motor steps includes a third motor step, and said third of said motor steps is divided into a third number of microsteps, and the third number of microsteps is less than the second number of microsteps.

29. In an intravenous delivery system comprising a fluid supply, a fluid supply line, and a fluid pump having a fluid pump step motor operating on the fluid supply line to move fluid through the line, a method for delivering fluid to a patient, comprising the steps of:

accelerating the fluid pump step motor in a series of motor steps, wherein a first of said motor steps is divided into a first number of microsteps, and a second of said motor steps is divided into a second number of microsteps, wherein the first number of microsteps is greater than the second number of microsteps; and

decelerating the fluid pump step motor in a series of decelerating motor steps, with a first of said decelerating motor steps is divided into a first number of decelerating microsteps, and a second of said decelerating motor steps is divided into a second number of decelerating microsteps, wherein the first number of decelerating microsteps is less than the second number of decelerating microsteps.