Patent Description:
A pivot drive is an electromechanical device which allows a controlled movement of an output element with respect to a reference element, e.g. a base. Preferably, the output element can be moved around all three axis of a Cartesian coordinate system.

Pivot drives can be used for many applications. One example is a gripper which is attached to the output element and which can be displaced with respect to the base of the pivot drive. The base of the pivot drive in turn can be connected to an arm of a robot.

One example of a prior art pivot drive is known from <CIT>. This known pivot drive is disadvantageous in that a displacement around one axis results in a translational displacement of another axis around which a displacement of the output element is possible. This complicates a displacement of the output element with respect to the base.

<CIT> discloses a motion-decoupled hydraulically driven three-degree-of-freedom spherical wrist with a rotation hydraulic motor, an angle sensor, a frame, a first displacement sensor, a tilting hydraulic pressure Cylinder, a tilting ring, a first connecting screw, a connecting rib, a second connecting screw, a side swing end cover, a first bearing, a second transmission shaft, an universal joint, a first transmission shaft, a coupling, a second bearing, a side swing hydraulic cylinder and second displacement sensor (<NUM>).

<CIT> shows a device for grinding solid workpieces, comprising a grinding wheel, a bearing, a grinding wheel driver, actuators and a digital control unit.

In <CIT> an artificial joint is disclosed having two components, one of which can rotate and can also flex relative to the other.

The object of the invention is to provide a pivot drive in which a controlled movement of the output element with respect to the base is possible.

In order to achieve this object, the invention provides a pivot drive comprising a base, an output element rotatable around an axis of rotation and pivotable around two or more axes, the pivot axes intersecting each other at a point of intersection which is arranged on the axis of rotation, and having a rotation actuator and two or more pivot actuators, the output element is supported on the drive element which in turn is supported on the base, the drive element being rotatable with respect to the base, the rotation actuator and the pivot actuators being mounted in a stationary manner with respect to the base. Arranging the pivot axes such that they intersect each other at a point of intersection which is arranged on the axis of rotation ensures that a displacement around one axis does not result in the other axis as such being in displaced in a translational manner. Ensuring that all axis intersect in a single point significantly simplifies the control of the displacement of the output element. Further, arranging all actuators in a stationary manner with respect to the base ensures that none of the motors used in the actuators is displaced, during a displacement of the output element, with respect to the base such that there is no issue with cables or conductors on which a bending load would act if the motors were displaced with respect to the base.

One of the displacements of the output element is a rotation around the axis of rotation, this displacement also being referred to as a yawing displacement. In order to achieve this movement, the output element can be mounted to a drive element in a manner so as to be pivotable with respect thereto but non-rotatably.

The drive element can be mounted rotatably with respect to the base, in particular by means of a cross-roller bearing. The bearing provides for a smooth, low friction and precise movement of the drive element with respect to the base. In case of a cross-roller bearing, the loads acting on the output element can be reliably transmitted to the base.

As an alternative to a cross-roller bearing, a sliding bearing or a simple roller bearing can be used.

The rotation actuator can be connected to the drive element by means of a gear arranged in the drive path between a rotation motor and the drive element. The gear allows to increase the torque provided by the rotation motor, thereby allowing the use of a compact rotation motor.

Depending on the requirements, the gear can be self-locking or non-locking. For a self-locking gear, a worm gear is particularly suitable.

According to an embodiment, the output element is mounted to the drive element by means of a cardan joint or a universal joint. This joint provides for torque transmission between the drive element and the output element while at the same time allowing the pivot movement of the output element with respect to the base.

As an alternative to the cardan joint or the universal joint, a constant velocity joint could be used.

According to an embodiment, a pivot ring is mounted to the output element so as to be rotatable with respect thereto around an axis which coincides with the axis of rotation of the output element. The pivot ring allows engaging at the output element so as to pivot it around the pivot axes in a mechanically very simple manner.

For moving the pivot ring with respect to the base, the pivot actuators engage at the pivot ring, in particular at an angle of <NUM>° with respect to each other. The combined action of the pivot actuators allows displacing the pivot ring and thus of the output element in all directions.

For displacing the pivot ring, each pivot actuator is operatively connected to an engagement element for engaging at the pivot ring, the engagement element being displaceable in a translational manner. This results in a mechanically simple structure of the pivot gear.

According to an embodiment, each pivot actuator is operatively connected to a gear for converting a rotational movement of the pivot motor into a translational movement of the engagement element. The gear allows introducing high actuation forces into the pivot ring while at the same time using a compact motor.

Depending from the requirements, the pivot gear can be a self-locking gear, in particular a spindle drive, or a non-locking gear.

For transferring the action of the pivot gears to the pivot ring, the engagement element of the pivot gear is one of a claw and a ball-shaped element. This mechanically simple structure allows to reliably transmit the movement of the engagement element to the pivot ring while at the same time allowing for a compensation of the movement of the claw and the ball-shaped element with respect to each other.

The pivot ring is preferably held non-rotatably with respect to the base in order to increase the position precision of the pivot gears.

Preferably, the pivot ring comprises an abutment element which engages between two or more guide surfaces, the guide surfaces being provided by the outer surfaces of the spindle drives. In this manner, a particularly compact construction is achieved which does not require space for a separate guide.

The spindles of the pivot gears can in particular extend perpendicularly to the plane of extend of the base which results in a space saving construction.

The axis of rotation of the motors can be arranged such that they are parallel to the central axis of the spindle drives and thus arranged on top of the base so as to accommodate the motor adjacent to the spindle drives, thus achieving a compact design.

In the alternative, the motors can be accommodated in the base of the pivot drive.

The invention will now be described with reference to two embodiments which are shown in the enclosed drawings. In the drawings,.

A first embodiment of a pivot drive <NUM> is shown in <FIG>.

Generally speaking, pivot drive <NUM> serves for displacing an output element <NUM> with respect to a base <NUM> of pivot drive <NUM>. Displacement of output element <NUM> is possible around the three axes of a Cartesian coordinate system (please see <FIG>), namely a rolling movement around an axis X, a pitching movement around an axis Y and a yawing movement around an axis Z. The movement around the axis z is in the following referred to as a rotation while the movement around axis x, y is in the following referred to as pivoting.

Base <NUM> can be mounted in a stationary manner. As an alternative, base <NUM> itself is arranged in a moveable manner, e.g. mounted to the end of an arm of a robot.

Output element <NUM> is intended to receive an element which is to be displaced by pivot drive <NUM>. In the first embodiment, a mounting bracket <NUM> is shown as connected to output element <NUM>. It can receive for example a mechanically actuated gripper.

Rotation is here possible by a range of ± <NUM>° (please see <FIG>) while a pivoting movement is possible with a range of ± <NUM>° (please see <FIG>) for example.

Output element <NUM> is supported on a drive element <NUM> which in turn is supported on base <NUM> so as to be rotatable with respect thereto.

For mounting drive element <NUM> in a rotatable manner on base <NUM>, a roller bearing <NUM> (only schematically depicted here) is used. The outer ring of bearing <NUM> is connected to base <NUM> (here by means of screws <NUM>; please see in particular <FIG>) while the inner ring of bearing <NUM> is connected to drive element <NUM>. Here again, screws can be used.

Roller bearing <NUM> is preferably a cross-roller bearing.

As alternative to a cross-roller bearing, a simple roller bearing can be used. It is also possible to use a slide bearing.

Irrespective of the particular type of bearing which is used, bearing <NUM> is adapted for precisely guiding drive element <NUM> with respect to base <NUM> while at the same time being able to support the loads which act on output element <NUM>.

Output element <NUM> is connected to drive element <NUM> in a manner which allows output element <NUM> to pivot with respect to drive element <NUM> while at the same time being connected thereto in a non-rotatable manner.

In the subject embodiment, a cardan joint or universal joint <NUM> is used for connecting output element <NUM> to drive element <NUM>.

Cardan joint <NUM> here comprises a cardan ring <NUM> which is connected to a drive head <NUM> of drive element <NUM> by means of a pin <NUM> which extends through drive head <NUM> and is oriented perpendicularly with respect to the axis of rotation of drive element <NUM>.

As an alternative to a single pin <NUM>, two shorter pins arranged on a common axis and protruding from opposite sides of drive head <NUM> could be used.

A second set of pins <NUM> with a common axis is arranged at an angle of <NUM>° with respect to the first pin <NUM>, with the second pins <NUM> connecting cardan ring <NUM> to output element <NUM>.

As an alternative to cardan joint <NUM>, a constant velocity joint could be used for connecting output element <NUM> to drive element <NUM> in a torque-transmitting but pivotable manner.

A rotation actuator is provided for rotating drive element <NUM> and consequently also output element <NUM> with respect to base <NUM>.

The rotation actuator comprises an electric motor <NUM> which preferably is a stepper motor.

As an alternative to a stepper motor, a servo motor or a similar motor can be used.

Rotation actuator <NUM> is connected to drive element <NUM> by means of a gear <NUM> (please see in particular <FIG>). Gear <NUM> here comprises a worm gear <NUM> which is driven by rotation actuator <NUM>, and a gear wheel <NUM> which engages into worm gear <NUM> and is connected non-rotatably to drive element <NUM>.

Gear <NUM> here is formed in a self-locking manner so that no brake or similar device is necessary for preventing rotation of output element <NUM> under external loads, when rotation actuator <NUM> is deactivated.

Should no self-locking properties of the gear be desired, different constructions can be used for connecting the rotation actuator <NUM> to drive element <NUM>.

In <FIG>, a stop pin <NUM> is visible which engages into an arc provided in gear wheel <NUM>. Stop pin <NUM> provides for a mechanical end stop which prevents excessive rotation of drive element <NUM> with respect to base <NUM>.

It is possible to mechanically rotate worm gear <NUM> without using rotation actuator <NUM>. To this end, a plug <NUM> is provided in base <NUM> which, when removed, provides access to an end face of the shaft on which worm gear <NUM> is arranged. The shaft can be turned by inserting a screw driver, an Allen key or a similar tool.

For pivoting output element <NUM> with respect to drive element <NUM>, at least two pivot actuators <NUM>, <NUM> are provided. In a manner similar to rotation actuator <NUM>, stepper motors are preferred. As an alternative, servo motors or similar drive devices can be used.

Generally speaking, pivot actuators <NUM>, <NUM> act on a pivot ring <NUM> which is connected to output element <NUM> in a manner so as to be rotatable with respect thereto. Preferably, a roller bearing <NUM> is used for mounting pivot ring <NUM> on output element <NUM>. Thus, any pivoting movement introduced into pivot ring <NUM> is transferred to output element <NUM>.

Pivot ring <NUM> is provided with two actuation projections <NUM> which here are arranged at an angle of <NUM>° with respect to each other (please see <FIG>). In the embodiment shown in the drawings, actuation projections <NUM> are spherical elements which are bolted to pivot ring <NUM>.

Arranging the actuation projections <NUM> at an angle of <NUM>° with respect to each other is advantageous in that the resulting lever arms for displacing the pivot ring <NUM> are at a maximum. It however is possible to use different angle, except for an arrangement where the actuation projections <NUM> are arranged (almost) diametrically with respect to each other.

At each actuating projection <NUM>, an engagement element <NUM> engages which here is formed as a claw (please see in particular <FIG> and <FIG>).

The actuating projections <NUM> are formed with a partially spherical shape which is engaged by at least two flat surfaces arranged opposite each other and in parallel with each other. This structure allows the actuating projections <NUM> to pivot with respect to the claws while at the same time being displaceable with respect thereto in a translational manner.

Each engagement element <NUM> is connected to a nut <NUM> which is arranged on a spindle <NUM>. Each spindle <NUM> is part of a spindle drive <NUM> or pivot drive which is used for displacing engagement element <NUM> in a translational manner.

Each spindle <NUM> (please see also <FIG>) is connected to the respective pivot actuator <NUM>, <NUM> by means of a gear <NUM> (please see <FIG>).

Each spindle drive <NUM> comprises a casing <NUM> which serves for preventing rotation of nut <NUM> when spindle <NUM> is rotated.

Pivot ring <NUM> is held non-rotatably with respect to base <NUM>, meaning that it cannot be rotated around the axis of rotation/center axis of output element <NUM>. In a simple embodiment, this could be achieved by supporting any torque via spindle drives <NUM>, in particular by means of the engagement between the actuating projections <NUM> and the claws <NUM>.

In order to achieve a higher precision, pivot ring <NUM> is here provided with an abutment element <NUM> which engages between the casings <NUM> of the spindle drives.

In a manner similar to the rotation drive, each spindle drive <NUM> is provided with an end cap <NUM> which allows, when removed, access to the end of the respective spindle so that the spindle can be rotated manually without operating the pivot actuators <NUM>, <NUM>.

A housing <NUM> is provided which seals all components of pivot drive <NUM> with respect to the environment. A flexible seal <NUM> is arranged between an edge of housing <NUM> and output element <NUM> so as to prevent contaminations from entering into housing <NUM>.

When both engagement elements <NUM> are displaced in the same direction, output element <NUM> performs a pivot movement around axis y. If one of the engagement elements is moved upwardly while the other one is moved downwardly, a pivot movement around axis y is performed. A suitable control of the displacement of the engagement elements <NUM> allows pivoting output element <NUM> in every direction.

Further, output element <NUM> can be rotated by operating rotation actuator <NUM>.

Any pivot movement takes place around axes which intersect each other at a point of intersection which is arranged on the axis of rotation of both output element <NUM> and drive element <NUM>. In other words, the point of intersection is arranged at the center of the cardan joint which connects drive element <NUM> to output element <NUM>.

As can be seen in <FIG>, the spindle drives are arranged such that the axes of rotation of the spindles <NUM> extend perpendicularly with respect to the plane of extent of base <NUM>. As can be further seen in particular in <FIG>, the axis of rotation of drive element <NUM> is also arranged perpendicularly with respect to the plane of extent of base <NUM>.

Actuators <NUM>, <NUM>, <NUM> are here arranged in parallel with the spindle drives <NUM>. Preferably, the axis of rotation of the motors used in actuators <NUM>, <NUM>, <NUM> is also arranged perpendicularly with respect to the plane of extend of base <NUM>.

The drive electronics used for controlling actuators <NUM>, <NUM>, <NUM> is preferably integrated into pivot drive <NUM>. They can in particular be arranged underneath housing <NUM> adjacent to actuators <NUM>, <NUM>, <NUM>.

A second embodiment of pivot drive <NUM> is shown in <FIG>. For all elements known from the first embodiment, the same reference numerals are used, and reference is made to the above comments.

The difference between the first and the second embodiment is that in the second embodiment, actuators <NUM>, <NUM>,<NUM> are not arranged on top of base <NUM> at the side of spindle drives <NUM> which is opposite output element <NUM>, but within base <NUM>. To this end, base <NUM> is increased in height so as to create the space which is necessary for accommodating the actuators <NUM>, <NUM>, <NUM> (and possibly also their associated drive electronics).

Claim 1:
A pivot drive (<NUM>) comprising:
a base (<NUM>); and
an output element (<NUM>) beingrotatable around an axis of rotation and pivotable around two or more pivot axes, the two or more pivot axes intersecting each other at a point of intersection which is arranged on the axis of rotation, and
wherein
the pivot drive (<NUM>) has a rotation actuator (<NUM>) and two or more pivot actuators (<NUM>, <NUM>), and
the output element (<NUM>) is supported on a drive element (<NUM>) which in turn is supported on the base (<NUM>), the drive element (<NUM>) being rotatable with respect to the base (<NUM>),
characterized in that
the rotation actuator (<NUM>) and the pivot actuators (<NUM>, <NUM>) are mounted in a stationary manner with respect to the base (<NUM>).