The laser cane.

During the past 30 years, at least 30 attempts have been made to build a useful mobility aid for the blind cane traveler (1,2) . All these efforts have resulted in only three aids showing sufficient promise to warrant serious evaluation : the Kay Binaural Sensory Aid (3,4), the Lindsay Russell' Pathsounder (5), and the Bionic Laser Cane . Why has the Laser Cane project been relatively more successful than so many of the others? The generalized answer to this question might help in guidance of future research in prosthetics and sensory aids — and a short history of this project may suggest an answer. In 1945 Lawrence Cranberg (6), then a physicist at the Signal Corps Electronics Laboratory, developed a single-channel optical ranging device to be used by the blind as an obstacle detector . It was quite ingeniously designed and well constructed, judged by the standards of the 1940's . In 1948 RCA built 25 of these "Signal Corps Devices" for the Veterans Administration, who then asked Thomas A . Benham, an outstanding blind physicist and engineer on the faculty of Haverford College, to evaluate them. His evaluation report (7), made in 1952, indicated that the instrument showed promise, but before it could even be looked at more critically, several important changes had to be made. As a result of this report, the Veterans Administration in 1953 requested Haverford College to have Professor Benham oversee the modifications required to carry out his recommendations . Haverford College, in turn, subcontracted the detail work to what is now Bionic Instruments . Thus began a long, slow, often frustrating journey, which, 10 devices and 16 years later, culminated in the first practical Laser Cane for the Blind. The basic design criteria for an obstacle detector established by Professor Benham in 1952 have been adhered to throughout the years and have proved sound . Paraphrased, they are: The device 1. must detect obstables and down-curbs; 2. must be silent and unobtrusive except when giving warning ;