TECHNICAL FIELD

The present invention relates to a telescopic shaft that is configured to connect a base of a parallel kinematics robot to an end effector of the same for the purpose of

transferring torque.

BACKGROUND ART

In parallel kinematics robots there is often a need to transfer torque from a stationary base to a tool on a movable end effector. Since the distance of the end effector from the base varies, telescopic shafts with a universal joint at each end are used for the purpose. It is

conventionally known to use telescopic shafts comprising no more than two shafts movable in relation to each other in an axial direction, such telescopic shafts being known e.g. from EP2716921A1, EP2301726A1 and DE102008019725A1.

A problem related to telescopic shafts in parallel

kinematics robots is that a telescopic shaft potentially limits a robot's working area. Telescopic shafts namely have their respective maximum and minimum lengths that in their turn define how far away from the base and how close to the base, respectively, the end effector can come. In telescopic shafts comprising no more than two shafts movable in

relation to each other in the axial direction the maximum length typically is about twice the minimum length.

There is a desire to allow an increased working area for a parallel kinematics robot by increasing the relation between the maximum and minimum lengths of the telescopic shaft, which in the following disclosure will be termed an

"extension factor".

SUMMARY OF THE INVENTION

One object of the invention is to provide an improved telescopic shaft for parallel kinematics robots. A further object of the invention is to provide an improved parallel kinematics robot.

These objects are achieved by the devices according to appended claims 1 and 13. The invention is based on the realization that a working area of a parallel kinematics robot can be increased by increasing an extension factor of a respective telescopic shaft. In order to enable extension factors larger than two, the number of shafts with mutual relative movements between the same in an axial direction needs to be more than two. Additional advantages can be achieved when the relative movements between different pairs of shafts are constrained in relation to each other in a predetermined way.

According to a first aspect of the invention, there is provided a telescopic shaft comprising a first shaft, a second shaft configured to enable a first relative movement in an axial direction between the first and second shafts, and a third shaft configured to enable a second relative movement in the axial direction between the second and third shafts, and a third relative movement in the axial direction between the first and third shafts. The second shaft is located between the first and third shafts. The telescopic shaft is configured to connect a base of a parallel

kinematics robot to an end effector of the same for the purpose of transferring torque. By providing the telescopic shaft with more than two shafts with mutual relative movements between the same, the extension factor and by that the working area of the parallel kinematics robot can be increased .

According to one embodiment of the invention the telescopic shaft further comprises constraining means configured to predetermine the first relative movement in relation to the second relative movement. By predetermining the sequence of movements between the shafts the telescopic shaft may be optimized e.g. to minimize the maximum relative velocity between the pairs of shafts, or to minimize the inertial loading caused by the telescopic shaft.

According to one embodiment of the invention, the first relative movement and the second relative movement are configured to occur simultaneously in sync with each other. According to one embodiment of the invention, the first relative movement and the second relative movement are configured to have same velocities at each instant. By this measure the maximum relative velocity between the pairs of shafts is minimized. According to one embodiment of the invention, the

constraining means comprises at least one of the following construction pairs: a line and a pulley pair, a chain and a sprocket pair, and a rack and a pinion pair.

According to one embodiment of the invention, the first relative movement and the second relative movement are configured not to occur simultaneously.

According to one embodiment of the invention, the third shaft is configured to fully extend in relation to the second shaft before the second shaft starts to extend in relation to the first shaft. By this measure the inertial loading caused by the telescopic shaft is minimized. According to one embodiment of the invention, the second shaft is configured to fully retract in relation to the first shaft before the third shaft starts to retract in relation to the second shaft. By this measure the inertial loading caused by the telescopic shaft is minimized.

According to one embodiment of the invention, the

constraining means comprises at least one of the following: an extension spring, a compression spring, gas spring, and a motor spring. According to one embodiment of the invention, the telescopic shaft further comprises balancing means configured to balance the effect of gravity.

According to one embodiment of the invention, the balancing means comprises at least one of the following: an extension spring, a compression spring, gas spring, and a motor spring .

According to one embodiment of the invention, the balancing means functions as constraining means configured to

predetermine the first relative movement in relation to the second relative movement.

According to a second aspect of the invention, there is provided a parallel kinematics robot comprising a base, an end effector and a telescopic shaft according to any of the preceding embodiments connecting the base to the end

effector.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail with reference to the accompanying drawings, wherein figure 1 shows a telescopic shaft according to one

embodiment of the invention, figure 2 shows a telescopic shaft according to one

embodiment of the invention, figure 3 shows a telescopic shaft according to one

embodiment of the invention, and figure 4 shows a parallel kinematics robot according to one embodiment of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring to figures la-Id, a telescopic shaft 10 according to one embodiment of the invention comprises a first shaft 20, a second shaft 30 and a third shaft 40, whereby all of the three shafts 20, 30, 40 are enabled to move in relation to each other in an axial direction 50 of the shafts 20, 30, 40. In radial direction all of the three shafts 20, 30, 40 are centred about a common longitudinal axis 60. A relative radial movement between the shafts 20, 30, 40 is prevented by means of wheels 70 on one shaft 30, 40 interacting with respective guide tracks 80 on another shaft 20, 30 of each neighbouring pair of shafts 20, 30, 40, and thereby torque can be transferred between each respective pair of shafts 20, 30, 40. The first shaft 20 comprises a first fixture 90 for attachment to a base 210 of a parallel kinematics robot 200 (see figure 4), and the third shaft 40 comprises a second fixture 100 for attachment to an end effector 220 of the parallel kinematics robot 200.

Referring to figure 2, the telescopic shaft 10 according to one embodiment of the invention comprises a pulley-line arrangement with a first and second cables 110, 120 fixedly attached to the first and third shafts 20, 40, and first and second pulleys 130, 140 rotatably attached to the second shaft 30. The first cable 110 interacts with the first pulley 130 in such a way that when the third shaft 40 retracts in relation to the first and second shafts 20, 30, the second shaft 30 is caused to retract in relation to the first shaft 20. Correspondingly, the second cable 120 interacts with the second pulley 140 in such a way that when the third shaft 40 extends in relation to the first and second shafts 20, 30, the second shaft 30 is caused to extend in relation to the first shaft 20. A relative

movement between the first and second shafts 20, 30 thereby occurs simultaneously in sync and with the same velocity as a respective relative movement between the second and third shafts 30, 40 at each instant. Instead of a pulley-line arrangement many alternative mechanisms can be used to achieve the function of predetermining the simultaneous sequence of relative movements between the shafts 20, 30, 40, such as a mechanism comprising a chain and a sprocket pair, or a rack and a pinion pair. Such mechanisms are known e.g. from US3118066A, US3244883A and US20110240817A1, the content of which is hereby incorporated into this disclosure by reference.

Referring to figure 3, the telescopic shaft 10 according to one embodiment of the invention comprises a spring

arrangement with a first extension spring 150 fixedly attached to the first and second shafts 20, 30. The first extension spring 150 exerts a pulling force between the first and second shafts 20, 30 in such a way that when the third shaft 40 extends in relation to the first and second shafts 20, 30, the second shaft 30 is caused to remain stationary in relation to the first shaft 20 until the third shaft 40 is fully extended in relation to the second shaft 30. Correspondingly, when the second shaft 30 retracts in relation to the first shaft 20, the third shaft 40 is caused to remain stationary in relation to the second shaft 30 until the second shaft 30 is fully retract in relation to the first shaft 20. A relative movement between the first and second shafts 20, 30 thereby never occurs simultaneously with a respective relative movement between the second and third shafts 30, 40. Instead of a spring arrangement

comprising one or more extension springs 150, 160 many alternative mechanisms can be used to achieve the function of predetermining the non-simultaneous sequence of relative movements between the shafts 20, 30, 40, such as a mechanism comprising one or more compression springs, or one or more motor springs .

Further referring to figure 3, the first extension spring 150 may also function as a balancing means that balances the effect of gravity. During a typical operation the telescopic shaft 10 is in a substantially vertical position with a hanging load, and gravity thereby acts to extend the

telescopic shaft 10. By dimensioning the first extension spring 150 appropriately the telescopic shaft 10 can at least partially balance the effect of gravity. The

telescopic shaft 10 of figure 3 further comprises a second extension spring 160 which has the sole function of

balancing the effect of gravity. For example, the second extension spring 160 can be dimensioned to at least

partially balance the effect of gravity, and the first extension spring 150 can be dimensioned to have a slightly larger spring constant than that of the second extension spring 160 so that it, in addition to predetermining the sequence of relative movements between the shafts 20, 30, 40, also contributes to balancing the effect of gravity.

A balancing means balancing the effect of gravity can be used in combination with any type of constraining means predetermining the sequence of relative movements between the shafts 20, 30, 40. For example, the telescopic shaft 10 of figure 2 can be provided with a member corresponding to the first extension spring 150 or the second extension spring 160 of the telescopic shaft 10 of figure 3. Instead of a spring arrangement comprising one or more extension springs 150, 160 many alternative mechanisms can be used to achieve the function of balancing the effect of gravity, such as a mechanism comprising one or more compression springs, or one or more motor springs.

The invention is not limited to the embodiments shown above, but the person skilled in the art may modify them in a plurality of ways within the scope of the invention as defined by the claims. For example, the telescopic shaft 10 may comprise more than three shafts 20, 30, 40 with mutual relative movements between the same in the axial direction, such as four or any other appropriate number of shafts 20, 30, 40.