Open-loop step motor control system

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.

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.

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.

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.sub.winding is the winding current, V.sub.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.

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.

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.

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.

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.sub.winding is the winding current, V.sub.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.