In-line conveyor scale with a primary first motor to provide constant torque, a secondary servo motor to provide fine-grained variable torque in response to a closed loop torque sensor, and a processor to assertain weight of an item conveved based on the closed loop servo motor response

A method for weighing a moving parcel comprising the steps of:

• providing a primary drive motor configured to provide a substantially constant first torque input to drive a conveyance at a substantially constant first velocity;
• providing a servo motor arranged to provide a variable second torque input to the conveyance, wherein the servo motor torque range is on the order of approximately an order of magnitude smaller than the first torque provided by the primary drive motor;
• providing a servo amplifier for controlling the servo motor in a closed-loop servo configuration;
• introducing a parcel on to the moving conveyance at a different velocity than the first velocity;
• monitoring a resulting change in motor current or torque provided by the servo motor;
• and
• determining a weight of the parcel based on the change in motor current or torque provided by the servo motor detected by the servo amplifier.

A method for weighing a moving parcel on the fly, comprising the steps of:

• providing a weighing conveyor belt for accelerating or decelerating the parcel as it rides on the weighing conveyor belt;
• providing a primary motor arranged to drive the weighing conveyor belt at a substantially constant first speed;
• providing a servo motor arranged in a closed-loop servo configuration so as to drive the weighing conveyor belt at the substantially first constant speed;
• summing torques provided by the primary motor and the servo motor to drive the weighing conveyor belt at the first speed;
• while the weighing conveyor belt is moving at the first speed, receiving a moving parcel on the weighing conveyor belt, the moving parcel initially moving at a velocity that is different from the constant first speed of the weighing conveyor belt;
• accelerating or decelerating the weighing conveyor belt so as to restore it to the first speed;
• sensing a torque provided by the servo motor to restore the weighing conveyor belt to the first speed;
• determining a weight of the parcel based on the sensed torque of the servo motor.