Method and apparatus for overspeed protection for high speed centrifuges

In a centrifuge system having a rotor mounted on a shaft, said shaft and rotor driven by a motor having an input current, and a speed control for receiving a user selected speed and accelerating said rotor from a stationary rotational velocity toward said user selected speed, a method of rotor protection through speed control comprising:

• accelerating said rotor from said stationary rotational velocity towards said user selected speed;
• taking a first speed measurement below said user selected speed at a first point in time during said acceleration;
• taking a second speed measurement below said user selected speed and at a speed exceeding said first speed measurement at a second point in time later than said first point in time during said acceleration;
• computing angular acceleration from said first and second speed measurements and said first and second points in time;
• measuring the current to said motor between said first and second points in time;
• computing the torque exerted on said motor using said measured current between said first and second points in time;
• computing from said angular acceleration and torque the moment of inertia of said rotor;
• utilizing the moment of inertia to look up a maximum speed limitation for said rotor;
• and,
• limiting the speed of rotation of said rotor to said maximum speed limitation when the maximum speed limitation is less than the user selected speed.

In the combination of a centrifuge system having a rotor mounted on a shaft, a motor for driving said shaft and accelerating said rotor to a user selected speed, and a control for controlling the acceleration of said rotor to said user selected speed, the improvement in said control comprising:

• means for determining the angular acceleration of said rotor over a preselected period of time;
• means for determining the torque exerted on said rotor during said preselected period of time;
• means for computing the moment of inertia of said rotor operably connected to said means for determining the angular acceleration and the means for determining the torque exerted on said rotor;
• means for determining from said computed moment of inertia of said rotor the maximum speed of rotation of said rotor;
• and,
• means for limiting the speed of the rotor to said maximum speed of rotation when the maximum speed is less than the user selected speed.

In a centrifuge system having a rotor mounted on a shaft, said shaft and rotor being accelerated by a motor toward a user selected speed, a method of rotor protection through speed control comprising:

• the steps of accelerating a suspect rotor towards said user selected speed;
• determining angular acceleration of said suspect rotor over a preselected time period;
• determining a torque exerted to accelerate said rotor over said preselected time period;
• computing from said angular acceleration and torque the moment of inertia of said rotor;
• utilizing said computed moment of inertia to determine a total kinetic energy limit of said rotor;
• computing the maximum speed of said rotor utilizing said total kinetic energy limit;
• and,
• limiting the speed of said rotor to said computed maximum speed when the computed maximum speed is less than the user selected speed.