A method for aligning the position of a movable arm includes: providing an
alignment element on the apparatus projecting a distance above the
apparatus in the z-direction and having a surface lying in a plane formed
by an x and y axis; providing a movable arm having a tool at the free
end; positioning the object such that the surface of the element faces
the tool; moving the tool in a direction towards the surface of the
element; sensing when the tool reaches a predetermined point on or above
the surface of the element, whereby the position of the tool in the
z-direction is determined based on the relationship between the measured
response of the tool and the height of the tool above the surface of the
alignment element; placing the tool on or at a distance in the
z-direction from the surface; moving the tool in the x-direction while
sensing the surface of the element; moving the tool in the x-direction
until an edge of the element is sensed; determining the center in the
x-direction based on the known distance the tool has moved and the known
dimensions of the element in the x-direction; placing the tool on or at a
distance in the z-direction from the surface; moving the tool in the
y-direction while sensing the surface of the element; moving the tool in
the y-direction until an edge of the element is sensed; determining the
center in the y-direction based on the known distance the tool has moved
and the known dimensions of the element in the y-direction. In a
preferred embodiment, the tool is a metering probe having a disposable
tip on the end thereof. In another preferred embodiment, the measured
response is the air pressure in the probe and the metering probe has a
source of compressed air for expelling air out of the end of the probe
and a pressure transducer for measuring the air pressure inside the
metering probe.