Coordinate measuring machine having auxiliary air bearing

A support system for a dimensional measuring machine comprising:

• a base;
• a carriage;
• a rail surface mounted to one of said base and carriage and extending in a first direction;
• a primary support system including a plurality of ball bearing assemblies for mounting said carriage to said base while allowing said carriage to be movable in the first direction with respect to said base, said ball bearing assemblies supporting said carriage on said base in two orthogonal directions which are each orthogonal to the first direction;
• and
• a secondary or auxiliary support system including:
• a housing mounted to the other of said base and said carriage, said housing having an orifice for receiving gas under pressure, a housing surface facing and in close proximity to said rail surface, said housing surface having a plurality of openings for the egress of gas therethrough and a gas passage for connecting the orifice with each of the openings, said gas passage allowing transmission of the pressurized gas from the orifice to the openings to provide an air cushion between and a gas force on the housing surface and the rail surface;
• and
• a spring element, a means for captivating under compression said spring element within the housing and between said housing surface and the other of said base and said carriage, whereby when the pressurized gas is applied to the orifice, the pressurized gas is directed to the openings in the housing surface creating an air cushion captivated between the rail surface and the housing surface, providing an air bearing therebetween, with the compression on the spring element approximately equaling the pressurized gas force, whereby the carriage may be moved in the first direction relative to the base over the air cushion and the force on the ball bearing assemblies is reduced by the auxiliary support system.

A method for improving repeatability in coordinate measuring apparatus by reducing the friction in mechanical bearings which mount a carriage to a base in the apparatus for relative movement therebetween, the steps of which method comprise:

• providing a housing having a passage leading from an inlet to a plurality of egress openings provided on a lower surface of the housing;
• mounting a rail to the base in proximity to the lower surface of the housing;
• mounting a biasing member between the housing and the carriage;
• applying a force to said biasing member for providing a repelling force between the housing and the carriage;
• and
• coupling a fluid under pressure to said inlet, whereby the fluid is transmitted through the passage to the plurality of openings on the lower surface of the housing to create a fluid force and a fluid cushion between the lower surface and the rail, said fluid force being approximately equal to the force of the biasing member, whereby the air cushion and biasing member reduce the friction in the mechanical bearings.

In combination with a measuring apparatus having a base, a carriage, means for mounting said carriage to said base for movement of the carriage relative to said base, said means including a plurality of bearing for supporting the carriage during movement, the improvement wherein at least one of said bearings for supporting said carriage is a bearing assembly comprising:

• mechanical bearings means for supporting said carriage in a first direction and a third direction and for allowing said carriage to move in a second direction;
• and
• air bearing means for supporting said carriage in the first direction and for allowing the carriage to move in the second direction, said air bearing means including:
• a rail mounted to one of said base at an adjustable incline with respect to said first and third directions and extending in said second direction;
• and
• a housing carried on the other of said carriage and said base, said housing having a plurality of passages connected together and each terminating in an aperture in a surface of said housing in contact with said rail, and means for receiving and directing air under pressure to said passages to direct air of said apertures and between said surface of said rail for creating an air cushion and an air force therebetween, whereby the air cushion between said rail and said surface allows the movement of the carriage in said second direction relative to the base with reduced friction on the mechanical bearing means which support the carriage in the first and third directions.