Ultrasonic sensor system

DETAILED DESCRIPTION OF THE INVENTION Referring to FIGS.
1 and 2, a doorway is shown in a wall W, the doorway including conventional framing, typically metal for commercial door fronts, which includes vertical risers 10 and 11 constituting a strike member and hinge member, respectively, and a horizontal support 12 with a swinging door 13 hingedly supported on vertical riser 11.
An approach side transducer 14 projects unidirectional beam 16 at an approach side detection zone ADZ at the approach side AP of the doorway DW and, upon detecting the approach of a person, energize door operator 18 which is coupled by a linkage 19 to the door 20 causing the door to swing open on an arc which includes the swingside departure area DA.
This departure area DA is normally protected by pairs of guard rails 21 and 22 and, in the prior art, some form of presence detector, typically a mat switch, microwave or infrared detectors and the like for detecting the presence of a person or object in the swinging path of door 20, which are replaced by the multiple transducer assembly incorporating the invention.
The transducers utilized in the preferred embodiment of this invention are low cost ultrasonic transducers of the type disclosed in my above referred to U.
S.
Pat.
No.
4,530,077 entitled "Efficient Low Cost Transducer System".
Such transducers are shown in FIGS.
6 and 7 hereof and, as shown in FIG.
6, a planar electrostatic acoustic transducer or generator 30, which, as noted above, in the preferred embodiment, is a Polaroid Corporation type electrostatic transducer, produces a conical ultrasonic beam at about 50 kHz that is approximately 10 degrees wide.
Transducer 30 is supported on an adjustable frame 31 so that it is already adjustable relative to the axis 32 of beam transformer 33.
In FIG.
7a, beam transformer 33 is a 45 degree cone reflector (90 degree apical angle) that is placed in the near field of the transducer 30 and the resulting beam acoustic axis lies in the plane normal to the axis of the cone and is in the direction of the displacement D (D=0), the resulting beam is omnidirectional in the normal plane; and when the displacement is very large (D=N), the resulting beam shape closely approximates the shape of the undisturbed transducer beam