Machine tools

Claim 2

In a machine tool, the combination comprising the base, a support movable on the base, a fixed stop on the base, a lead screw on said base for moving the support on the base toward and away from the stop, first drive means operable to drive the lead screw at a first speed, second drive means operable to drive the lead screw at a second speed less than the first speed, first clutch means energizable to provide a driving connection between said second drive means and said lead screw, second clutch means provided between said second drive means and said first clutch means and being normally operable to provide a driving connection between said second drive means and said first clutch means, said second clutch means being operable upon engagement of the support with the stop with a predetermined force to disengage the drive between said second drive means and said first clutch means, said second clutch means comprising a worm, bearing means mounting said worm for unlimited rotation and limited axial movement, a worm wheel meshing with said worm and with said lead screw, and a clutch providing a driving connection between said second driving means and said worm, the helix angle of the worm and the worm wheel being such as to preclude driving of the worm by the worm wheel, said last-mentioned clutch comprising a first clutch member connected to said second driving means a second clutch member connected to said worm, said first and second clutch members being engaged and disengaged by axial motion of said worm, spring means urging the worm axially to engage said first and second clutch members and to maintain the clutch members in engagement when the load on the worm wheel does not exceed a predetermined maximum, said spring being adapted to permit disengagement of the clutch member when the worm wheel stops due to excess torsion load thereby causing the worm to move axially relative to the worm wheel and causing the moment of inertia of the worm and associated parts to overrun the worm such as to disengage the clutch members.

Claim 3

The combination set forth in claim 1 including a third clutch operable upon axial movement of the worm in an opposite direction and functioning to disengage the driving connection from said second driving means when the torsional load in the opposite direction exceeds a predetermined amount.

Claim 4

In a transmission: a driving worm, a driven worm wheel, a source of rotational power for said worm, a torsional load driven by said worm wheel, said torsional load having a maximum normal value and subject to excursions exceeding said normal maximum, a transmission housing, bearings in said transmission housing for supporting said worm for unlimited rotation and for restricted axial movements, a first clutch member attached to said source of rotational power, a second clutch member attached to said worm, said first and second clutch members being frictionally engaged and disengaged by the axial motion of said worm, spring means adapted to urge the worm axially to engage said first and second clutch members, said spriNg means being pre-stressed to maintain the clutch members engaged when the load on the worm wheel does not exceed the said normal maximum, the said pre-stress of the said spring being further adapted to permit disengagement of said clutch members when the worm wheel stops due to excess torsional load thereby causing the worm to move axially as a screw, relative to teeth of the stopped worm wheel and the moment of inertia of the said worm and attached parts being sufficient to cause overrun of the worm whereby the said clutch parts are completely disengaged.

Claim 5

In a transmission: a driving worm, a driven worm wheel, a source of rotational power for said worm, a torsional load driven by said worm wheel, said torsional load having a maximum normal value and subject to excursions exceeding said normal maximum, a transmission housing, bearings in said transmission housing for supporting said worm for unlimited rotation and for restricted axial movements, a first clutch member attached to said source of rotational power, a second clutch member attached to said worm, said first and second clutch members being frictionally engaged and disengaged by the axial motion of said worm, spring means adapted to urge the worm axially to engage said first and second clutch members, said spriNg means being pre-stressed to maintain the clutch members engaged when the load on the worm wheel does not exceed the said normal maximum, the said pre-stress of the said spring being further adapted to permit disengagement of said clutch members when the worm wheel stops due to excess torsional load thereby causing the worm to move axially as a screw, relative to teeth of the stopped worm wheel and the moment of inertia of the said worm and attached parts being sufficient to cause overrun of the worm whereby the said clutch parts are completely disengaged.

Claim 6

In a machine tool, the combination comprising the base, a support movable on the base, a fixed stop on the base, means for moving the support on the base toward and away from the stop, first drive means operable to drive the moving means at a first speed, second drive means operable to drive the moving means at a second speed less than the first speed, first clutch means energizable to provide a driving connection between said second drive means and said moving means, second clutch means provided between said second drive means and said first clutch means and being normally energized to provide a driving connection between said second drive means and said first clutch means, said second clutch means being operable upon engagement of the support with the stop with a predetermined force to disengage the drive between said second drive means and said first clutch means, said moving means comprising a lead screw, said second clutch means comprising a worm, bearing means mounting said worm for unlimited rotation and limited axial movement, a worm wheel connected to said lead screw and meshing with said worm, and a clutch providing a driving connection between said second driving means and said worm, the helix angle of the worm and the worm wheel being such as to preclude driving of the worm by the worm wheel, said clutch comprising a first clutch member connected to said second driving means, a second clutch member connected to said worm, said first and second clutch members being engaged and disengaged by axial motion of said worm, spring means urging the worm axially to engage said first and second clutch members and to maintain the clutch members in engagement when the load on the worm wheel does not exceed a predetermined maximum, said spring being adapted to permit disengagement of the clutch member when the worm wheel stops due to excess torsion load thereby causing the worm to move axially relative to the worm wheel and causing the moment of inertia of the worm and associated parts to overrun the worm such as to disengage the clutch members.

Claim 7

In a machine tool, the combination comprising the base, a support movable on the base, a fixed stop on the base, means for moving the support on the base toward and away from the stop, first drive means operable to drive the moving means at a first speed, second drive means operable to drive the moving means at a second speed less than the first speed, first clutch means energizable to provide a driving connection between said second drive means and said moving means, second clutch means provided between said second drive means and said first clutch means and being normally energized to provide a driving connection between said second drive means and said first clutch means, said second clutch means being operable upon engagement of the support with the stop with a predetermined force to disengage the drive between said second drive means and said first clutch means, said moving means comprising a lead screw, said second clutch means comprising a worm, bearing means mounting said worm for unlimited rotation and limited axial movement, a worm wheel connected to said lead screw and meshing with said worm, and a clutch providing a driving connection between said second driving means and said worm, the helix angle of the worm and the worm wheel being such as to preclude driving of the worm by the worm wheel, said clutch comprising a first clutch member connected to said second driving means, a second clutch member connected to said worm, said first and second clutch members being engaged and disengaged by axial motion of said worm, spring means urging the worm axially to engage said first and second clutch members and to maintain the clutch members in engagement when the load on the worm wheel does not exceed a predetermined maximum, said spring being adapted to permit disengagement of the clutch member when the worm wheel stops due to excess torsion load thereby causing the worm to move axially relative to the worm wheel and causing the moment of inertia of the worm and associated parts to overrun the worm such as to disengage the clutch members.

Claim 8

The combination set forth in claim 4 including a third clutch operable upon axial movement of the worm in an opposite direction and functioning to disengage the driving connection from said second driving means when the torsional load in the opposite direction exceeds a predetermined amount.

Claim 9

The combination set forth in claim 4 including supplemental inertia means on said worm.