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DC Motor Drive System Control Methods

DC Motor Drive System Control Methods - Motors&Drives.book...

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Chapter 6: Drive System Control Methods 231 Drive System Control Methods Introduction Up to this point, basic drive theory, component hardware, and interface devices have been discussed. It is now time to put the basics to work to develop a drive system. The following information will help tie the compo- nents together into a coordinated control system. All systems configura- tions would be closed loop because of the precise speed and torque regulation required. In actuality, there would be many more pieces to the system “puzzle” than what is presented here. However, this section is meant to present a general outline of drive systems and how the pieces work together in an auto- mated environment. Coordinated Drive Systems It is helpful to start with what could be considered a “simple” system and move to the more complex. Figure 6-1 indicates one such simple closed- loop system. As seen in Figure 6-1, this is a “widget” manufacturing facility. This section is the “finishing” section of the system, with proximity sensors strategically placed along the out-feed conveyor. All of the sensors are connected to an amplifier unit that sends contact signals to the drive. The drive needs to know where the widget is at all stages of the system. Therefore, the job of the proximity sensor is to send a contact closure signal to the drive. This would be considered a digital input (DI). In this case, the drive does not need to know how big, or how long the widget is, just that fact that it has arrived at a particular station on the conveyor. Once the drive has deter- mined the widget has finished all processes, it can then send a relay output signal to the warehouse, alerting that the widget is on its way.
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232 Motors and Drives In this case, the operator sends a speed reference to the drive. The drive operates the motor at that speed until the widget reaches the first proxim- ity sensor. At that point, the contact closure signal indicates the widget has arrived at the labeling section. The drive takes the contact closure and operates at a preset speed 1 (slower speed), so the label section has time to perform its function. Once the widget exits the label section, another proximity sensor “opens” the preset speed contact, and the conveyor returns to normal speed. The process is repeated when the widget enters the sorting section. At this point, another digital input is closed, which signals the drive to switch to preset speed 2. At the output of the sorting section, another proximity sen- sor closes. This indicates that the widget is ready for the warehouse, and the drive returns the conveyor to normal speed. This is a somewhat crude system but could be considered a coordinated sys- tem . The drive could be either DC or AC, along with the corresponding motor. Similar configurations would be seen on packaging systems, food processing systems, and any application where process speed may differ from part movement speed. Later in this chapter, a view of a more auto- mated system will be presented.
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DC Motor Drive System Control Methods - Motors&Drives.book...

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