Developing a Remote-Controlled CASE CX-160 Excavator Using National Instruments FieldPoint

Author(s):
Chris Terwelp - Virginia Tech University

Industry:
University/Education

Products:
Compact FieldPoint, LabVIEW, FieldPoint

The Challenge:
Developing a remotecontrolled excavator with six independent movements that provide the operator real-time visual feedback while removing explosive materials at a remote site 1,000 miles away. shutdown circuit to fulfill the safety requirement of this application. FieldPoint

The Solution:
Using radio modems to connect National Instruments FieldPoint distributed I/O modules at both sites, as well as NI LabVIEW software for processing and transmitting joystick inputs to the excavator.

Introduction
The Naval Surface Warfare Center at Dahlgren, Virginia asked us to develop an excavator to remove chemical and explosive hazards located at the test facility. Safety concerns suggested that we remove the hazardous materials using a remote-controlled excavator at a remote location to minimize the exposure of chemical and explosive hazards to the equipment operator. In addition, the design of the excavator should include six independent movements, vision capabilities, operating parameters, and remote ignition and emergency stop links.

CASE CX-160 Excavator
The Case CX-160 excavator operates by conventional means with two dual-axis joysticks and two single-axis foot pedals. Each of these axes actuate through two stages of hydraulic spool valves. The excavator has six independent movements: arm, boom, bucket, swing, and left and right track. To control these movements, we placed both FieldPoint modules at the operator station and in the excavator. We then loaded programs on the FieldPoint modules that convert joystick inputs to excavator movements. A FieldPoint distributed I/O system operates at 10 Hz and controls the six independent movements at the remote location. Electrical power is available in 12 and 24 volts with a maximum current of 45 amps. We used an independent emergency shutdown circuit to fulfill the safety requirement of this application.

FieldPoint Development and LabVIEW Software Design
To ensure stability and overall safety, we wanted to remotely control the robust excavator controllers in real time. When designing the CASE CX-160 excavator, we selected FieldPoint distributed I/O modules to remotely control the robust controllers of the excavator in real time to ensure stability and overall safety. The FieldPoint modules, in conjunction with LabVIEW and LabVIEW Real-Time, provide intelligent operation, as well as the failsafe conditions that the CX-160 excavator requires.

We also selected an electronic sensing and acquisition system that consists of various FieldPoint distributed I/O modules that link together using FieldPoint network modules. FieldPoint distributed I/O quickly facilitates client-based systems through simple integration with LabVIEW. FieldPoint modules communicate through Ethernet and serial data transfer protocols, while data transmits between modules through wireless serial radio modems. An Ethernet connection monitors the FieldPoint modules.

The basic excavator operation reads analog voltages from control input devices at the remote station. Industrial joysticks and foot pedals provide control for the six-independent movements. The FP-AI-100 analog voltage input device reads control data at rates up to 350-Hz, a speed that is crucial for reliable digital control, while the FP-2000 Real-Time series network module initiates the data acquisition process. The analog voltage then travels across the network for implementation on the excavator FieldPoint modules.

The ExcavatorOperator Station
At the remote operator station, the operator uses the FieldPoint FP-DI-300 discrete input module to facilitate ignition control. With this module, the operator can remotely toggle the power of vision systems and work lights. Four joystick buttons provide pan-and-tilt capabilities for the excavator cameras. Various case structures assign incoming data a level of priority.

After this new control data receives a level of priority, the new control data then transmits via SRM-6000 serial radio modems. These radio modems operate in the 900 MHz band at ranges up to 25 miles. These radio modems support asynchronous data transfer rates up to 115.2 Kbps, a necessary feature for stable control of the excavator. A frequency hopping spread spectrum transmission algorithm and a proprietary signal gain provide immunity to radio interference.

Upon receiving information from the wireless link, an additional FP-2000 network module running a different real-time VI processes the data. This data, which is formatted in ASCII strings, contains identifiers that distinguish its meaning and destination. The control of the ignition sequence occurs by interfacing the CX-160 start/stop relays with the FieldPoint FP-RLY-420 relay module. This relay also controls the work lights and the camera pan/tilt utility. An additional relay module sends power to cameras and audio/video transmitters. The excavator network module controls the hydraulic proportional valves through the FieldPoint FP-AO-210 analog voltage output module. This voltage then passes to a solenoid-operated valve controller, thus facilitating basic vehicle control.

To ensure the vehicle is running at capacity, the operator must monitor vehicle parameters, such as fuel level, water and oil temperature, and warning messages in real time. These parameters are normally displayed on an on-board liquid crystal display next to the joystick. CASE design engineers, in conjunction with Sumitomo engineers, developed software to report this data via an available RS-232 port located on-board the excavator’s computer. The unused FieldPoint Ethernet connection monitors the status of the excavator through the use of a serial-to-Ethernet converter. The data is then processed and sent back across the wireless network to the remote site where proper action is taken. If a critical error occurs, the vehicle control terminates and warning messages display for the operator.

A Windows-based PC running a third LabVIEW VI monitors the excavator by reading information on the remaining remote side FP-2000 Ethernet port. The PC acts as a monitoring device, which reduces strain on the real-time series processor. It can also actuate limited control upon the vehicle. The operator can monitor the excavator through any PC with either LabVIEW or a Web browser.

Summary
Five undergraduate students and one graduate student working part-time implemented this concept in five months. FieldPoint and LabVIEW Real-Time software helped us easily implement a remote control for the excavator. FieldPoint modules help advance the development of tele-operated applications. Systems can run independent of each other or they can collectively work together as a team. The FieldPoint design facilitates quick and easy programming and provides watchdog timers and power-on reset tools that ensure failsafe operation. Normally, it is a challenge to digitally control an application, but with FieldPoint distributed I/O, it is easy to maintain system stability, even in great distances.

For more information, contact:

Chris R. Terwelp

Virginia Tech University

Department of Mechanical Engineering

113 Randolph Hall

Blacksburg, VA 24061

Tel: (540) 231-6637

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