Method and system for controlling rotational speed of an agitator or catheter

A method of limiting torque of a catheter assembly with a rotational profile, the method comprising:

• rotating the catheter assembly at a target rotational speed according to an initial peak current and a starting value for an initial current limit for a motor, the starting value for the initial current limit being less than the initial peak current;
• limiting, by the processor, a motor current during a rotational period of the catheter assembly to the initial current limit after the initial peak current;
• calculating, by a processor, the motor current of the motor during a rotation of the catheter assembly in a first direction;
• and
• changing, by the processor, the initial current limit of the motor as a function of the initial current limit based on the calculated motor current by the processor when the calculated motor current of the motor during the rotation of the catheter in the first direction is less than the initial current limit of the motor.

A device handle for cutting substances inside a body lumen, the device handle comprising:

• a slide assembly, the slide assembly including a drive shaft assembly configured to rotate a catheter assembly, a motor configured to impart a rotational force to the drive shaft assembly and the catheter assembly, and a processor, wherein the processor is configured to:
• rotate the catheter assembly according at an initial peak current and a first current limit, the first current limit being less than the initial peak current, and wherein initial peak current and the first current limit are configured to attain a target rotational speed in a first direction;
• limit an actual current value during a rotational period of the catheter assembly to the first current limit in the first direction after the initial peak current;
• calculate the actual current value during the rotational period of the catheter assembly with the first current limit in the first direction;
• change the first current limit in the first direction to a second current limit in the first direction when the calculated actual current value by the processor during the rotational period of the catheter assembly with the first current in the first direction is lower than the first current limit in the first direction;
• when a rotational speed in the first direction is not achieved at the target rotational speed, changing by the processor, a first current limit in the second direction that is higher than the first current limit in the first direction calculated by the processor when driving the catheter assembly so that the catheter assembly attains the target rotational speed in a second direction;
• and
• alternate the driving of the catheter assembly between the first direction and the second direction.