New programmable sensor uses ultrasonics Essay

New programmable sensor uses ultrasonics

A new acoustic sensing system for detection, identification,
verification, and measurement of parts has been introduced by Cochlea Corp, San Jose, CA.

Called Sonovision , the system– configured much like an
optoelectronic (machine vision) system–can be used for tasks such as
measuring flatness, depth of holes, bends in sheet-metal parts, shapes
of internal cavities, and the dimensions of odd-shaped parts such as
castings and forgings.

According to Dr Shawn Buckley, president of Cochlea Corp and
developer of the system, the repeatable accuracy of Sonovision is
typically 0.001 for positioned parts.

“We can achieve higher accuracy in certain cases,
however,’ says Buckley. “For instance, we’ve been able to
measure the flatness of silicon wafers to within one micron. In order
to achieve this kind of accuracy, though, we need a flat part and
perpendicularity between the sensor head and the part.’

Parts to be measured by the system typically have maximum
dimensions of 0.25 to 6.0, but larger objects can be measured with
custom sensor arrays.

Speed of inspection can range up to 50 parts/sec.

The components

A basic Sonovision system consists of a sensor head and a
microprocessor-based controller. The standard sensor head (see photo)
consists of nine small ultrasonic transducers mounted in a grid array on
one side of the head. The head measures 3H 5W 2.5D. Other heads are
available for localizing the sensing region to small parts or wide

Measuring 5.5 H 17 W 17 D, the controller comes in configurations
for table or rack mounting. For on-line operation, the controller has
16 parallel input and output signals as well as one RS-232C serial port.
The controller can process signals from up to six sensor heads at once
with optional expansion ports and software.

Sonovision can also be operated off-line. The operator then uses
front-panel instruments and/or a video monitor.

Power requirements are 200 W for the controller at 115 VAC, 60 Hz;
the sensor heads are powered by the controller.

How it works

To program the system, the operator simply positions a part under
the sensor head and presses a button on the controller. A transmitter
in the head emits ultrasonic waves toward the part; some of the waves
echo from the part, return to the transducers, and form an analog
picture or signature for the part.

If the part will be presented in any of several orientations, the
operator acquires a signature for each of the critical orientations.

The controller digitizes the phase and amplitude data for each
orientation, and stores them in memory. Up to 25 signatures can be
stored at the same time.

Cochlea Corp now offers units that utilize ultrasonic waves of 20
kHz, 0.5 wavelength, and 40 kHz, 0.25 wavelength. “We’ll soon
introduce a unit operating at 80 kHz, 0.125 wavelength,’ Buckley
says. “Generally speaking, the higher the frequency, the greater
the resolution.’

In operation, a part approaching the inspection station triggers a
sensor that turns on the transmitter. Usually the parts are stopped
under the sensor head, but the system can also perform on moving parts.
Each action–presence-detection, measurement, inspection, etc–requires
just 1/60th sec.

Ideally, the distance between the sensor head and the subject will
be fixed at a predetermined distance. This is usually less than 1, but
can be as great as 6 for low-resolution measurements.

Measures ID precisely

Buckley reports that beta field-test installations were completed
in June of this year, and that several large corporations have ordered
Sonovision systems for laboratory and training applications.

Typically the first system costs $30,000 to $40,000. Multiple
systems in one facility or for one type of application cost $20,000 or
less per system.

“For measuring flatness, the acoustic method is usually more
precise than optoelectronic vision,’ Buckley says. “Acoustic
sensing is also a more accurate method for measuring the depth of holes,
the internal dimensions of bores, and deviations from standards.

“If the user wants to measure bends and hole sizes in formed
sheet-metal parts, for example, Sonovision would be a good choice.’

Sonovision systems are now available for delivery. For full
details, circle E1

Photo: A standard, nine-microphone sensor head sits atop a
Sonovision controller. Each controller can process inputs from up to
six heads simultaneously.

Photo: There are two ways Sonovision could be used in feeding,
inspecting, and sorting. At top, one sensor head coarsely sorts and
orients parts as they leave the feeder, deflecting misoriented or bad
parts back into the bowl (as shown in the insert at lower right). At
left center, a second sensor head accurately inspects the parts and
allows only good parts to pass through. In qualification applications,
parts usually need not be oriented.

Photo: Schematic shows how Sonovision interfaces through a
programmable-logic controller with various automated equipment for
sorting, feeding, machining, and handling.


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