Abstract: A tool-carrying vehicle, such as a road grader, is provided with an apparatus for maintaining a predetermined distance between its blade or other tool and a laser reference plane generated by a rotating laser beam. The apparatus includes a detector housing supported on a mounting extending upwardly from the blade, a detector support frame on the housing, a laser reference plane detector on the support frame, and electrical control circuitry. The mounting is movable to permit moving the detector housing relative to the vehicle in response to tool movement.The laser reference plane detector has first and second spaced apart laser beam detecting arrays. The detector may be provided with upper and lower movable carriages with one of the arrays positioned on each carriage, permitting the carriages to converge and diverge to vary the distance separating the detecting arrays and thereby control the degree of accuracy required of the tool.

Abstract: A land-surveying apparatus for use with a laser beam source to obtain grade and range distances has a grade pole with a laser beam detection unit slidably mounted thereon, electrical measuring means being connected between the grade pole and the detection unit to generate an electrical grade signal representative of the grade distance between a detector using an array of phototransistors and the base of the grade pole. A digital display unit receives the grade signal, processes it, and digitally, visibly displays the information contained in the signal. Electrical grade calculating circuitry is provided to process first and second grade signals containing the elevation of the upper and lower edges of the laser beam relative to the base of the pole and arithmetically process the signals to obtain the elevation of the laser beam center which is then displayed as the grade distance.

Abstract: A control system for a spring-applied service brake which can also be used as a parking brake. Pressure from the vehicle hydraulic system is normally used to release the brakes. In the event of a loss of the primary pressure from the hydraulic system, the control system switches automatically to use of secondary pressure from the vehicle compressed air system to release the brakes, while maintaining the ability of the operator to apply the brakes by normal operation of the service and parking brake controls.