Using PXI and LabVIEW Real-Time to Automate Gauge Control in Cold Rolling Mills

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"After evaluating various platforms for this complex application, we chose NI PXI real-time technologies to save our clients time and money."

- Shekhar Patil, Pitel Engineering Pvt. Ltd.

The Challenge:
Implementing a compact, closed-loop control system that continuously operates with minimum human intervention to monitor and control gauges online in cold rolling mills.

The Solution:
Developing a PXI-based gauge monitoring and control system using the NI LabVIEW Real-Time Module and NI data acquisition (DAQ) PXI hardware.

Shekhar Patil - Pitel Engineering Pvt. Ltd.

This cold rolling mill gauge control system used in ferrous and nonferrous metal industries to obtain metal strips (in the form of coils) of uniform thickness requires high-precision monitoring. The system primarily monitors the thickness of the metal sheet in real time and controls the gauge with very short response time.

The system has one fixed roll and one movable roll connected to a hydraulic cylinder. The movable roll uses an input signal to apply the pressure required on the steel sheet to ensure the correct gauge.

After evaluating various platforms for this complex application, we chose NI PXI real-time technologies to save our clients time and money.

System Description

The system uses various sensors. The thickness gauges measure the thickness of the metal strip and provide the data as analog voltages (deviation from the set point in microns). The pressure sensor provides information on the pressure applied by the hydraulic cylinders as an analog voltage.

The digital data coming from the position transducers determines the position of the hydraulic cylinders, indirectly measuring the gauge of the metal (or the gap between the rolls). The encoder attached to the rotating deflector roll indicates the speed at which the strip rolls out.

Figure 1 depicts the cold rolling setup and the various signals. We designed an automatic gauge control system that uses the data received from the sensors to vary the hydraulic pressure to control the gauge of the metal strip.

System Hardware

The control system uses a PXI controller running LabVIEW Real-Time. The PXI system houses several different modules. The NI PXI-6040E analog I/O module assimilates the thickness and pressure data. The NI PXI-6602 timing module counts the data from the encoders to measure the speed of the strip, and pulses from position transducers to measure the cylinder movement. The NI PXI-6711 analog output module controls servo valves, which in turn control the hydraulic cylinder to change the cylinder’s position, moving the roll vertically to control the thickness. Another hardware design challenge was providing a regular push button control panel to use in times of contingency, such as when the real-time system connection to the host fails. We met this challenge by using the NI PXI-6527 digital I/O module. Figure 2 illustrates the system hardware.

System Software

For software development, we chose LabVIEW Real-Time because it is simple, yet powerful. We developed the VIs, then deployed them to the PXI controller running on LabVIEW.

The benefits of using LabVIEW software and PXI DAQ hardware instead of traditional instruments and programmable logic controllers (PLCs) include the following:

  • Reducing development time for the whole system (down by a factor of 1/6) reduced cost of man hours
  • Increasing flexibility in redesigning the control mechanism per the requirements of different materials fed to the system
  • Enhancing output quality because of reduced response times (typical PLC-based system has 100 to 500 ms control loop rate, but NI PXI-based system has 10 ms control loop rate)
  • Synchronizing all hardware on the PXI real-time system integration (RTSI) bus

Author Information:
Shekhar Patil
Pitel Engineering Pvt. Ltd.
128, Vardhaman Industrial Complex, Gokul Nagar, LBS Marg
Tel: +912225375776

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