This invention relates in general to pneumatic control apparatus; and, more particularly, to an improved two-button air logic control for a machine or the like.
The prior art teaches two-button control systems for various machines which require the use of both hands thus ensuring an operator's hands are clear of machine operation. There are known systems which combine pneumatic control operation with mechanical control operation. For example, a safety control mechanism for use in controlling the operation of power driven machinery requires the simultaneous operation of two handles controlling air valves of a pneumatic system. Further, mechanical engagement between the handle and the controlled machinery is used in conjunction with the air control valves to prevent undesired operation. Such a system has an undesirably high degree of complexity and requires fabrication and maintenance of both pneumatic and mechanical systems.
Use has also been made in the prior art of a purely pneumatic system having two control buttons for controlling operation of hazardous machines. Nevertheless, although only two control buttons have been required, typically the pneumatic control system includes three or more valves in combination with exhaust ports and orifices of restricted cross section. For example, there is typically a two stage operational sequence using two palm button operated valves which operate two or three relay valves which in turn supply an output signal; that is, manually operated valves activate other valves which produce an output for controlling a machine. Further, in some such systems orifices having equally matched cross sectional areas are required. Such requirements add to the cost and complexity of a pneumatic control system. Indeed, more generally, fabrication and maintenance of such systems typically have an undesirable degree of complexity and a correspondingly undesirable high cost. Thus, the problem of having a simple, low cost pneumatic control system has not been effectively solved. These are among the deficiencies of existing control systems the present invention overcomes.