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John Deere: Soil Bin Test System
Products Used:
PXI - 1000B 8 slot chassis
PXI - 8176B PXI RT Controller
PXI - 6052E Multifunction IO Card
PXI - 6533 Digital IO Card
PXI - 6602 Counter - Timer Card
PXI - 6713 Analog Output Card
SCXI - 1001 Chassis
SCXI - 1520 Strain Gage Analog Input Module (Qty 3)
SCXI - 1102 Analog Input Module
SCXI - 1126 Frequency Input Module
SCXI - 1162HV Digital Input Module (Qty 2)
SCXI - 1163R Digital Output Module (Qty 2)
Abstract:
V I Engineering worked closely with John Deere to develop a LabVIEW RT based system to aid in the design and testing of agricultural implements. The system allows John Deere to test implements throughout the year in an indoor Soil bin. The soil bin contains soil that can be prepared with controlled moisture content, density, and other properties. A specially designed carriage (tool carriage) is used to carry instrumentation, sensors, toolplates, and the implement to be tested. Another carriage (refit) is used to prepare the soil to the desired conditions using tools such as a roller and a tiller. The carriages are moved along the length of the bin by a drive mechanism consisting of DC motor, transmission mechanism, and pulley driven steel cables. The tool carriage travel at speeds typical to what implements experienced in the field. The PC based system, developed by V I Engineering, using National Instruments PXI and SCXI hardware and LabVIEW RT software, controls the entire test process of moving the carriages, controlling the tool plates, and measuring high-speed data. Three Window 2000 based PC's and a single RT PXI controller are used to control, acquire, and analyze up to 218 analog and digital signals. Communication between the computers is accomplished via DataSockets, TCP and VI Server.
The Challenge:
To develop a PC based test system capable of performing tests on agricultural implements while controlling the motion of a 9 kN (2000 lbs) carriage in an in-door soilbin. The test system needs to be flexible enough to allow users to configure test parameters, while being robust enough to control the carriage at typical implement travel speeds
The Solution:
V I Engineering developed a solution using National Instruments PXI and SCXI hardware. Three Window 2000 based PCs and one PXI RT controller were networked together in a client-server architecture using software developed with LabVIEW. LabVIEW RT was used to control the I/O operations needed for the test and carriage control.
System Requirements:
The new soil bin system was intended to replace a 30 year old system thereby improving on its capabilities and performance. The major requirements for the system are:
- Utilize soft panels to provide flexibility in configuration of tests, and allow for better display options.
- Control of critical devices under real-time conditions. The main drive motor, gears, toolplate motors, penetrometer, tiller and roller drives, are some of the devices that need real-time control.
- High-speed data acquisition of load cells and strain-gages used to characterize the load response of the implement tested.
System Description:
Figure1 shows the software and hardware architecture developed for the system.
The main computer is a Windows 2000 PC situated in the control room. The main PC is used for performing test setup, channel setup, and is also responsible for data logging during a test. The main PC handles all non-data acquisition and control functions for the system, and also acts as the server in the network. A user can configure a download test parameters to the RT system which performs the actual I/O required to conduct a test. See Figure 2 for a sample User Interface screen for test setup.
In addition to the main PC, there are also two remote Panel PCs. One Panel PC is situated in the control room, and the other Panel PC is mounted on a panel that moves along the tool carriage. The main PC performs as a server for the remote Panel PCs. The main PC runs a National Instrument's DataSocket server. The remote PCs communicate user interface events such as button presses, data input etc, via DataSockets to the Main PC. See Figure 3 for a sample User Interface screen that runs on a Panel PC.
The RT system handles all interfacing to the external hardware via PXI and SCXI modules. The LabVIEW application that runs on the embedded PXI controller, performs continuous data acquisition and control of all DAQ and SCXI channels. Communications between the main PC and RT system is via Ethernet and uses VI Server functions of LabVIEW. Test parameters are passed between the two via VI globals, which are LabVIEW VIs that use shift-register to store data. The VIG use semaphores in case all three PCs need to communicate to the RT system.
The system is capable of operating in three basic modes, namely, computer, main, and carriage. The name reflects the PC that is in command of the carriage.
During software development there were a few challenges with the RT application development as well as with the communications. Channel configuration using virtual channels posed problems in the RT system and caused unpredictable behavior of system crashes. These problems were largely fixed by upgrading to NI-DAQ 6.9.3.
The communication between the RT System and the main PC was initially accomplished using DataSockets. While this approach was very simple from a programming perspective, it was not well suited when there are a large number of channels. After experimenting with TCP/IP to send/receive data between the Main PC and the RT System, this approach was also abandoned due to. The most successful communication method was using the VI Server functions in LabVIEW. Using this, the main PC can invoke methods and properties of a VI Global running on the RT system to get/put data. This approach resulted in very robust communications between the two pieces of software. DataSocket method was used only for communications between the remote Panel PC and the main PC, where the data transfer rates were less critical and traffic not as high.
Following is a sequence of a typical test in the Soil-Bin:
From the Carriage panel
1. Prepare the soil to the desired conditions
2. Set the tool to the appropriate setup
From the Main PC
1. Set the test parameter
2. Perform pre-run operations
3. Perform the test
The main benefits derived from the new Soil Bin system arise primarily from using a software-based control and DAQ system as against a traditional hardwired controller. The new system allows considerably more flexibility in changing test parameters, and provided a host of analysis, data-logging, and display features that were not available in the previous system. The system also allows for future expansion and upgrades as it is built on an industry standard and expandable hardware platform. The system is expected to be in use for at least 10 years, therefore maintainability is a very important aspect for selecting this solution.
Conclusion:
The Soil-bin system is a one of a kind, very complex control system that needed considerable ingenuity and dedication to develop. By using National Instruments LabVIEW and PXI/SCXI hardware, several of the complexities in user interfaces, I/O operations, real-time control, and communications were solved to provide a very flexible, robust, and maintainable system.
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