WATER JET CONFERENCE - Waterjet Technology Association

The machine thrust load is measured by two custom-built load links installed on
the clevis mounts of two opposite thrust actuators. The internally gaged load links only
respond to the horizontal load components on the actuators and therefore output is not
affected by the change in geometry resulting from forward movement of the cutterhead.
The cutterhead torque measurement is accomplished with a diaphram-type
pressure transducer which monitors the hydraulic oil pressure on the two drive motors.
The pressure reading is then converted to cutterhead torque using manufacturer supplied
performance charts for drive motors.
The steering angle is measured by a linear potentiometer which actually measures
the linear displacement on the steering actuator. Through a simple lever arm ratio, this
displacement is then converted to a corresponding steering angle of the cutterhead. As
with torque output, this conversion is again accomplished by the computer.
The cutterhead rpm is monitored by a magnetic pickup transducer installed on the
main bearing housing. By knowing the time interval between successive pulses, the
computer then calculates the rotational speed of the cutterhead.
The cutterhead penetration into the rock is measured using an ultrasonic
displacement transducer, which provides information about the location of the cutterhead
with respect to a fixed starting point. The computer again converts this information to a
corresponding penetration rate value.
A unique feature of the rotary cutting machine is the capability to monitor and
measure various cutter forces. Presently, the machine is fitted with 8 load cell assemblies
installed on selected cutters on the cutter head. These are triaxial load cells capable of
measuring three orthogonal force components, vertical, side and rolling on individual
cutter assemblies. The load cells were designed and developed at CSM and have proven
extremely reliable in past laboratory and field instrumentation programs. They are totally
enclosed with steel cover plates and are sealed to provide protection against rock chips or
moisture. Temperature compensation is provided through the use of full-bridge circuitry
for each load channel. The load cells were designed to incorporate high loading capacity
while maintaining excellent measurement sensitivity to any direction of load.
The transfer or cutter force data from load cells to the data acquisition system is
accomplished by means of a multi-channel wireless telemetry device. The system
basically consists of a multiplexer/signal conditioner, a transmitter and a
receiver/demodulator unit. In operation, data from load cells is sampled at a rate of 6400
readings per second, digitized and transmitted serially in a modified NRZ Pulse-Code
format consisting of synchronization information and 16 data words. At the receiver end,
the data is then decoded and reconverted into analog voltages which are presented in
parallel and continuous fashion updated with each sampled value. These data are then fed
into the computer for storage on hard disc.
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