Robotic tool changer coupling mechanism with increased torsional rigidity and reduced freeplay
To substantially eliminate torsional freeplay in a robotic tool changer having a ball-lock coupling mechanism, scallop-like features in the form of cross-contact recesses are formed in at least one of, and preferably both of, a bearing race in a tool assembly at the points of contact of rolling members, and in the opposing inner surfaces of bores containing the rolling members in a master assembly. The cross-contact recesses are sized and shaped to receive a rolling member, but have a central void, or channel, perpendicular to the rolling member's motion in torsional freeplay, which does not contact the rolling member. The cross-contact recess contacts the rolling member at contact areas on either side of the central void. These contact areas impart two separate contact forces on the rolling member, both angled toward the center of the rolling member and hence operative to prevent side-to-side movement, or rocking, of the rolling member within the cross-contact recess, and hence substantially eliminating torsional freeplay of the robotic tool changer.
1. A robotic tool changer, comprising:
a tool assembly including a bearing race;
a plurality of spherical rolling members;
a master assembly including a plurality of bores, each configured to contain one of the plurality of spherical rolling members, and a cam having at least one tapered surface angled so as to urge the rolling members against the bearing race to couple the master and tool assemblies, and to allow the rolling members to retract away from the bearing race to decouple the master and tool assemblies;
wherein at least one of an inner surface of each of the plurality of bores and a corresponding plurality of positions on the bearing race include a cross-contact recess configured to seat a corresponding one of the rolling members when the master and tool assemblies are coupled;
wherein each of the cross-contact recesses of the plurality of bores or corresponding plurality of positions on the bearing race is generally cylindrical or spherical concave and has substantially a same radius as one of the plurality of spherical rolling members, and comprises a central void that does not contact the one of the plurality of spherical rolling members and two three-dimensional contact areas, each having a three-dimensional contact surface, one on either side of the central void, both of which contact the one of the plurality of spherical rolling members over respective corresponding three-dimensional contact areas of the one of the plurality of spherical rolling members when the master and tool assemblies are coupled, wherein each of the three-dimensional contact areas is greater than a point or line of contact.
2. The robotic tool changer of claim 1 wherein the central void is a concave channel.
3. The robotic tool changer of claim 1 wherein the central void is a rectangular channel.
4. The robotic tool changer of claim 1 , wherein both of the inner surface of each bore and the corresponding plurality of positions on the bearing race include the cross-contact recesses of the plurality of bores or corresponding plurality of positions on the bearing race.
5. The robotic tool changer of claim 4 , wherein when the master and tool assemblies are coupled, for each of the rolling members, the cross-contact recess in the inner surface of the corresponding bore and the cross-contact recess at the corresponding one of the plurality of positions on the bearing race together exert four forces on the rolling member, all directed toward a center of the rolling member.
6. A method of a coupling master assembly and tool assembly of a robotic tool changer, comprising:
moving a plurality of spherical rolling members disposed in bores in the master assembly into contact with a bearing race of the tool assembly when the master and tool assembly are abutted by advancing a cam having at least one tapered surface angled so as to urge the spherical rolling members against the bearing race to couple the master and tool assemblies; and
seating each of the plurality of spherical rolling members in a cross-contact recess formed in at least one of an inner surface of each of the bores and at a plurality of corresponding positions on the bearing race;
wherein each cross-contact recess of the bores or plurality of corresponding positions on the bearing race is generally cylindrical or spherical concave and has substantially a same radius as one of the plurality of spherical rolling members, and comprises a central void that does not contact the one of the plurality of spherical rolling members and two three-dimensional contact areas, each having a three-dimensional contact surface, one on either side of the central void, both of which contact the one of the plurality of spherical rolling members over respective corresponding three-dimensional contact areas of the one of the plurality of spherical rolling members when the master and tool assemblies are coupled, wherein each of the three-dimensional contact areas is greater than a point or line of contact; and
wherein retracting the cam allows the spherical rolling members to retract away from the bearing race to decouple the master and tool assemblies.
7. The method of claim 6 wherein the central void is a concave channel.
8. The method of claim 6 wherein the central void is a rectangular channel.
9. The method of claim 6 , wherein seating each of the plurality of rolling members comprises seating each of the plurality of rolling members in the cross-contact recess of the bores or plurality of corresponding positions on the bearing race formed both in the inner surface of the corresponding bore and at one of the plurality of corresponding positions on the coupling surface of the bearing race.
10. The method of claim 9 , wherein when the master and tool assemblies are coupled, for each of the plurality of rolling members, the cross-contact recess of the bores or plurality of corresponding positions on the bearing race in the inner surface of the corresponding bore and the cross-contact recess of the bores or plurality of corresponding positions on the bearing race at the corresponding one of the plurality of positions on the bearing race together exert four forces on the rolling member, all directed toward a center of the rolling member.