Safety system for a machine tool

Claim 1

A safety system for a machine tool of the type including a machining head and a table mounted adjacent said machining head for powered movement through a path extending along a region of said machine tool, towards and away from said machining head, and fixed structure adjacent said machining head, said table and fixed structure having sides projecting laterally to the side of said machining head to create pinch areas in which the leading side of the table moves towards said machining head, and a safety system for conditionally shutting down said machine tool upon intrusion of a person into said pinch areas, including means stopping said powered movement of said table, said safety system characterized by ultrasonic transmitter means periodically transmitting an ultrasonic pulse from said leading side of said table into said pinch area, ultrasonic receiver means for receiving echo signals from objects in the pinch area, and safety circuit means for triggering a machine tool shutdown including stopping said powered movement of said table upon receiving an echo signal from an object within an accurately predetermined range from said leading side of said table, said predetermined range being a small proportion of the extent of said powered movement of said table along said path towards and away from said fixed structure, said safety circuit means including timer means creating an interval of limited duration only during which interval an echo signal from a transmitted pulse will produce a machine shut down, whereby said safety circuit means is not responsive to echo signals from objects outside of said range to create a shifting safety zone substantially less than the extent of movement of said table along said path, and whereby entry of a person into portions of said pinch areas which are out of said safety zone does not result in a machine tool shut down.