Few of us give much thought to the mechanism that keeps the door of our car
secure, yet easy to open when we want to get in or out. That mechanism,
usually known as a latch, is a vital link in the chain of safety that is an
essential part of modern cars. Not only must the latch operate smoothly and
easily under normal conditions, it must hold the doors closed during an
As a major supplier of latches to car manufacturers in the UK and Europe,
ArvinMeritor produces six hundred latches an hour, twenty hours a day, five
days a week all of which must be tested before being released for delivery
to the customer. Just one out of spec latch in a delivery can result in the
whole batch of several thousand being rejected, not to mention the damaging
effect on the company’s reputation. One hundred per cent testing at this
rate of production must be an automated part of the total production process
and ArvinMeritor turned to Kistler Instruments for a reliable, workable and
affordable solution to the problem.

The solution ArvinMeritor senior engineer, Terry Heynes, and Kistler
application engineer, Eddie Jackson, developed was to use a piezoelectric
sensor to measure the force needed to actuate the latch and a miniature
linear displacement sensor to measure the distance travelled during latch
operation. The output from the force and displacement sensors being fed
into a Kistler CoMo IIS system that monitors the data to ensure that the
force at critical points of operation is within specification. The CoMo IIS
displays the curve of force against displacement and the preset values to
provide an instant, visual confirmation that the system is operating
Once a latch has been confirmed within specification, a laser coder burns a
unique identifier onto the latch body. Any latch failing, passes through
the laser coder without being marked. At the end of the line, each latch is
presented to a packer as accepted or rejected and is placed by hand into the
appropriate bin. To ensure that the latches are placed in the correct bin,
all rejected latches must pass through a light beam sensor mounted above the
reject bin. If this does not happen, the line is stopped until the error is
rectified. All rejected latches are passed to a manual test station for

All the data collected by the CoMo IIS, linked to the unique identifier for
each latch, is uploaded to the company’s mainframe computer via an Ethernet
LAN. The data on every latch is retained in archive so that any failures
can be traced back to the point of manufacture easily and reliably at any
time in the future. This is especially important in the event of a product
liability claim as it allows confirmation that any individual latch was
within specification when it left the Arvin Meritor plant.

Senior engineer, Terry Heynes, says that automatic, quality control
monitoring is essential to keeping tight control of production costs,
essential in a highly competitive market. The Kistler sensors and CoMo IIS
system provide a very cost effective solution to the problem of reliable
product testing at high production rates and generates the data needed for
protection against the possibility of future product liability claims.

Kistler Instruments Limited
Established in Wintherthur (Switzerland) in 1957, Kistler is represented in
over 50 countries and has subsidiaries in Germany, France, Italy, UK, Japan,
USA, China, Korea and Singapore.

Heavy investment in research and development, 15% of staff worldwide are
engaged in research and development, has generated a number of innovations
using piezoelectric, piezoresistive and capacitive techniques to provide
solutions to numerous force, pressure and acceleration measuring problems.
These innovations include the world's first commercial quartz sensor,
two-wire constant current technology to integrate sensors with
microelectronic circuitry, high-temperature pressure sensors for use up to
400 Deg C and three-component force measuring sensors.

More information is available from:-

Kistler Instruments Limited
Alresford House, Mill Lane. Alton GU34 2QJ UK
Telephone: +44(0)1256 741550
Fax: +44(0)1256 741551

Web Site:

January 2005

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