Centrifuge motor control

Details Centrifuge motor control Centrifuge motor control

2001-03-30

2003-01-14

Nappi, Robert E. (Department: 2837)

Electricity: motive power systems

Braking

Dynamic braking

C318S376000, C318S700000, C318S729000, C318S799000, C318S800000, C318S802000, C318S803000, C210S360100, C210S380100, C494S007000, C494S008000, C494S009000

Reexamination Certificate

active

06507161

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates in general to heavy cyclical centrifugal machines and, more particularly, to an apparatus for controlling the speed and direction of a rotating centrifugal basket of the machine. While the present invention is generally applicable to heavy cyclical centrifugal machines, it will be described herein with reference to batch centrifugal machines used for manufacturing and refining sugar.
A centrifugal machine uses centrifugal force to separate substances, such as, for example a liquid component (the filtrate) from a solid component (the cake), in a slurry which has been introduced to the centrifugal machine. A filtering perforate wall traps the cake by a filter, whereas the filtrate passes through the filter.
A problem encountered when operating heavy cyclical centrifugal machines of the type used to manufacture and refine sugar is the inaccurate control of the speed of rotation of centrifugal baskets of the machines. These baskets should be fully loaded to their maximum capacities to maximize the productivity of the machines. Unfortunately, should the rotation of the centrifugal basket inadequately dispel the filtrate, the cake may be compromised. Variations in the loading properties of the charge material, massecuite for sugar manufacture and refining, can affect the efficiency of cycle to cycle centrifugal processing. Since these variations in loading properties are difficult or impossible to control, it has been an ongoing goal in the industry to control the motor operations of centrifugal machines such that the machines may be loaded with maximum charge in spite of the charge material variations.
The operational speeds of a heavy cyclical centrifugal machines are known to be established through the use of 2-speed motors, which utilize a dual set of internal windings such that the motor may operate at either a low or a high speed. However, a portion of a typical centrifugal machine cycle may require the rotational speed of the basket to be maintained at some intermediate value on the low speed windings. One known method of accomplishing this task is to repeatedly open and close a set of electrical contacts that energize and de-energize the low speed windings. This causes wear on the electrical components and may require frequent maintenance.
Further, it is a practice to reverse the direction of rotation of the centrifugal machine basket while discharging the charge material from the centrifugal machine basket. This is typically implemented by mechanically braking the rotation of the centrifugal machine basket until the centrifugal machine basket is at rest. The main 2-speed motor is electrically disengaged, and a second motor is engaged to rotate the centrifugal machine basket in the reverse direction. Upon completion of the discharge phase of the centrifugal machine cycle, the second motor disengages and the 2-speed motor re-engages to start a new cycle. Thus, the cost of the centrifugal machine is increased, and the motor control circuitry is complicated by the need to switch between multiple motors during each cycle.
Additionally, peak power demands, which occur typically during accelerating the centrifugal basket, can cause considerable power drain. This is because engaging the 2-speed motor low or high speed windings amounts to “across-the-line” starting of the motor. This has the effect of huge current demand on the electrical transformer during motor acceleration. The power drawn during operation affects the refiners ability to process sugar cost efficiently.
Accordingly, there is a need for an improved motor control for a centrifugal machine that eliminates the need for a second motor for operating the basket is a reverse direction, and reduces the peak power drawn by the centrifugal machine.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages of previously known motor controllers for centrifuge machines wherein a motor controller is provided for a centrifuge machine including a logic control module, one or more power cells, and one or more contactors. The logic control module is capable of interfacing with the main centrifuge controller and provides control over the power cells and contactors to provide a voltage ramp-up to accelerate the centrifuge basket. As such, the logic control module avoids the current draining problems associated with across the line starting of the centrifuge motor. The power cells receive a voltage from the main power supply, and output to the contactors variable power to control centrifuge motor speed. Further, the configuration of multiple contactors to reverse the power supplied to the centrifuge motor windings may eliminate the need for a second, reverse direction motor.
In accordance with one embodiment of the present invention, a motor controller for a centrifuge machine comprises a first power cell having an input coupled to a main power supply, and an output. The first power cell is switchable between an on state where power is supplied to the output, and an off state where no power is supplied to the output. The motor controller also comprises a first contactor connected between the output of the first power cell and first windings of a motor. The first contactor is switchable between a first state, wherein an electrical connection is made between the first power cell and the motor, and a second state wherein an electrical connection is broken between the first power cell and the motor. Additionally, the motor controller comprises a logic control module coupled to the first power cell and the first contactor. The logic control module is arranged to interface with the controls of the centrifuge machine to selectively apply and vary power to the motor. Power is supplied to the motor when the logic control module switches the first contactor to the first state to establish an electrical connection between the first power cell and the motor. The logic control module further communicates with the first power cell to vary the power output by the first power cell, and accordingly adjusts the power to the motor thereby controlling the rotation of the centrifuge. For example, where the first power cell is implemented as a pair of silicon controlled rectifiers (SCRs), the logic control module controls the amount of power the first power cell supplies to the motor by varying the rate at which the logic control module turns the first power on and off.
When used with certain heavy duty cylindrical centrifugal machines, three phase AC power may be required to power the motor. Under such circumstances, the motor controller further comprises second and third power cells. The power supply comprises a three phase power supply and each of the first, second and third power cells couple a respective phase of the three phase power supply to the first contactor.
Further, more elaborate motor control schemes may be realized by incorporating into the motor controller a second contactor connected between the first power cell and second windings of the motor. The second contactor is switchable between a first state, wherein an electrical connection is made between the first power cell and the motor, and a second state wherein an electrical connection is broken between the first power cell and the motor. The second contactor is coupled to the logic control module. The logic control module is further arranged to control the first and second contactors for selectively supplying power to the first and second windings of the motor. For example, the motor may be a 2-speed motor having first windings, which are low speed windings connected to the first contactor. The second windings may be high speed windings connected to the second contactor. The logic control module is arranged to switch both the first and second contactors into their respective second states, thus the motor controller supplies no power to the motor. By maintaining the second contactor in the second state, and turning the first contactor to the first state, the power cell is coupled to the first (low speed) motor win

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