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Title:
A TELESCOPIC SHAFT FOR A PARALLEL KINEMATICS ROBOT
Document Type and Number:
WIPO Patent Application WO/2017/178051
Kind Code:
A1
Abstract:
A telescopic shaft (10) comprises a first shaft (20) and a second shaft (30) movable in relation to the first shaft (20) in an axial direction (40). A clockwise wheel set (70) exerts force on the first shaft (20) when the second shaft (30) rotates clockwise (80) about a longitudinal axis (90) of the second shaft (30), and a counter-clockwise wheel set (100) exerts force on the first shaft (20) when the second shaft (30) rotates counter-clockwise (110) about the longitudinal axis (90). Each of the clockwise wheel set (70) and the counter-clockwise wheel set (100) comprises a plurality of wheels (50) configured to roll against guide tracks (60) on the first shaft (20). Each of the wheels (50) is configured to always contribute in transmitting torque between the first and second shafts (20, 30) either when the second shaft (30) rotates clockwise (80) or when the second shaft (30) rotates counter-clockwise (110). The telescopic shaft (10) is configured to connect a base (210) of a parallel kinematics robot (200) to an end effector (220) of the same.

Inventors:
OLSSON, Mats (Isblocksvägen 5, Västerås, 722 31, SE)
Application Number:
EP2016/058190
Publication Date:
October 19, 2017
Filing Date:
April 14, 2016
Export Citation:
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Assignee:
ABB SCHWEIZ AG (Brown Boveri Strasse 6, 5400 Baden, 8050, CH)
International Classes:
F16C3/035; B25J17/02; B25J18/02; F16C29/04; F16D3/06; B23Q1/54; B25J9/00
Foreign References:
DE2705331A11978-08-10
JP2007162871A2007-06-28
DE102006030105A12008-01-03
EP2301726A12011-03-30
DE102008019725A12009-10-29
US20110240817A12011-10-06
US20140096636A12014-04-10
US3478541A1969-11-18
US2983120A1961-05-09
JP2007162871A2007-06-28
Attorney, Agent or Firm:
SAVELA, Reino (ABB AB, Intellectual PropertyIngenjör Bååths Gata 11, Västerås, 721 83, SE)
Download PDF:
Claims:
CLAIMS

A telescopic shaft (10) comprising:

a first shaft (20),

a second shaft (30) movable in relation to the first shaft (20) in an axial direction (40),

at least one clockwise wheel set (70) configured to exert force on the first shaft (20) when the second shaft (30) rotates clockwise (80) about a longitudinal axis (90) of the second shaft (30), at least one

counter-clockwise wheel set (100) configured to exert force on the first shaft (20) when the second shaft (30) rotates counter-clockwise (110) about the longitudinal axis (90), each of the clockwise wheel set (70) and the counter-clockwise wheel set (100) comprising a plurality of wheels (50) configured to roll against guide tracks (60) on the first shaft (20), and each of the wheels (50) being configured to always contribute in

transmitting torque between the first and second shafts (20, 30) either when the second shaft (30) rotates clockwise (80) or when the second shaft (30) rotates counter-clockwise (110),

characterized in that the telescopic shaft (10) is configured to connect a base (210) of a parallel

kinematics robot (200) to an end effector (220) of the same .

A telescopic shaft (10) according to claim 1, wherein the wheels (50) rotate about wheel axes (140) that are immobile in relation to the second shaft (30) .

A telescopic shaft (10) according to any of the

preceding claims, wherein the wheel axes (140) are parallel to, but offset from, a radial direction (135) of the longitudinal axis (90) .

4. A telescopic shaft (10) according to any of the

preceding claims, wherein each clockwise wheel set (70) and each counter-clockwise wheel set (100) comprises at least three wheels (50) . 5. A telescopic shaft (10) according to any of the

preceding claims, wherein the wheels (50) in each wheel set are symmetrically distributed about the longitudinal axis (90) .

6. A telescopic shaft (10) according to any of the

preceding claims, wherein the at least one clockwise wheel set (70) is offset from the at least one counter¬ clockwise wheel set (100) in a direction perpendicular to a radial direction (135) of the longitudinal axis (90), the offset (150) being fixed. 7. A telescopic shaft (10) according to any of the

preceding claims, wherein the second shaft (30)

comprises at least two clockwise wheel sets (70) and at least two counter-clockwise wheel sets (100).

8. A telescopic shaft (10) according to any of the

preceding claims, wherein the guide tracks (60) have a length of at least 10 cm, such as at least 20 cm, at least 30 cm, at least 40 cm or at least 50 cm.

9. A telescopic shaft (10) according to any of the

preceding claims, wherein the second shaft (30) is at least partially within the first shaft (20) .

10. A telescopic shaft (10) according to any of the

preceding claims, wherein the telescopic shaft (10) further comprises a third shaft (190) being movable in relation to the second shaft (30) in the axial direction (40), at least one clockwise wheel set (70) configured to exert force on the second shaft (30) when the third shaft (190) rotates clockwise (80) about a longitudinal axis (90) of the third shaft (190), at least one

counter-clockwise wheel set (100) configured to exert force on the second shaft (30) when the third shaft (190) rotates counter-clockwise (110) about the

longitudinal axis (90) of the third shaft (190), each of the clockwise wheel set (70) and the counter-clockwise wheel set (100) comprising a plurality of wheels (50) configured to roll against guide tracks (60) on the second shaft (30), and each of the wheels (50) being configured to always contribute in transmitting torque between the second and third shafts (30, 190) either when the third shaft (190) rotates clockwise (80) or when the third shaft (190) rotates counter-clockwise (110) .

11. A telescopic shaft (10) according to claim 10, wherein the third shaft (190) is at least partially within the second shaft (30) .

12. A parallel kinematics robot (200) comprising a

telescopic shaft (10) according to any of the preceding claims .

13. A parallel kinematics robot (200) according to claim 12, wherein the telescopic shaft (10) connects a base (210) of the parallel kinematics robot (200) to an end

effector (220) of the same.

Description:
A telescopic shaft for a parallel kinematics robot 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.

BACKGROUND ART

In parallel kinematics robots there is often a need to transmit rotational movement 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 pair of universal joints are used for the purpose. It is conventionally known to use an axial bushing such as a ball spline bushing in combination with a grooved steel shaft. The bushing allows axial movement but prevents radial movement in relation to the shaft. The ball spline nut has a plurality of small balls rotating at a high speed during the relatively fast movements of a typical parallel kinematics robot, and this generates wear and heat. The balls circulate within the ball spline nut such that their axes of rotation move both in relation to the shaft and in relation to the ball spline nut at relative movement of the two, and only part of the balls at a time contribute in transmitting torque between the ball spline nut and the shaft. It also becomes necessary to lubricate the full length of the shaft. Another design used for telescopic shafts is to use low friction material in the contact surface between the inner and outer parts, and transmit the torque with e.g. splines. Such design allows a high torque transmission but is not optimized for high axial speeds because of the sliding contacts between the parts. There is a risk for wear and heat generation.

US20140096636A1 discloses a parallel kinematics robot with a telescopic shaft comprising a combination of a rail member and a slider. The slider includes a plurality of cylindrical rolling elements circulating within the slider such that their axes of rotation move both in relation to the rail member and in relation to the slider at relative movement of the two, and only part of the rolling elements at a time contribute in transmitting torque between the rail member and the slider. The rolling elements have relatively small diameters. Also documents US3478541A and US2983120A disclose circulating rolling elements.

JP2007162871A discloses a telescopic steering shaft with a male shaft, a female shaft, and two torque transmitting means interposed in between the two such that torque can be transmitted allowing a free movement in the axial direction. The torque transmitting means for different directions are arranged on separate elements with an energizing spring affecting in circumferential direction in between in order to remove an angular play from between the two shafts. The axial movement appears to be relatively short and slow.

There remains a desire to mitigate the problems experienced in telescopic shafts connecting a base and an end effector of a parallel kinematics robot because of the wear and heat generated in the telescopic shafts during relatively long and fast movements.

SUMMARY OF THE INVENTION

One object of the invention is to provide an improved telescopic shaft for connecting a base and an end effector of a parallel kinematics robot, which improved telescopic shaft generates little wear and heat, and can be implemented using low cost components.

These object is achieved by the device according to appended claim 1. The invention is based on the realization that when torque between two shafts is transmitted through wheels that do not need to be circulated, the wheels can be made much larger in diameter without increasing the dimensions of the shafts.

According to a first aspect of the invention, there is provided a telescopic shaft comprising: a first shaft, a second shaft movable in relation to the first shaft in an axial direction, at least one clockwise wheel set configured to exert force on the first shaft when the second shaft rotates clockwise about a longitudinal axis of the second shaft, at least one counter-clockwise wheel set configured to exert force on the first shaft when the second shaft rotates counter-clockwise about the longitudinal axis, each of the clockwise wheel set and the counter-clockwise wheel set comprising a plurality of wheels configured to roll against guide tracks on the first shaft, and each of the wheels being configured to always contribute in transmitting torque between the first and second shafts either when the second shaft rotates clockwise or when the second shaft rotates counter-clockwise. The telescopic shaft is

configured to connect a base of a parallel kinematics robot to an end effector of the same.

Since each of the wheels is configured to always contribute in transmitting torque between the first and second shafts either when the second shaft rotates clockwise or when the second shaft rotates counter-clockwise, the wheels do not need to be circulated. Consequently, the wheels can be dimensioned large in diameter without increasing the dimensions of the shafts. Wheels with large diameters are less sensitive to dirt and do not require lubrication.

According to one embodiment of the invention, the wheels rotate about wheel axes that are immobile in relation to the second shaft.

According to one embodiment of the invention, the wheel axes are parallel to, but offset from, a radial direction of the longitudinal axis.

According to one embodiment of the invention, each clockwise wheel set and each counter-clockwise wheel set comprises at least three wheels.

According to one embodiment of the invention, the wheels in each wheel set are symmetrically distributed about the longitudinal axis. According to one embodiment of the invention, the at least one clockwise wheel set is offset from the at least one counter-clockwise wheel set in a direction perpendicular to a radial direction of the longitudinal axis, the offset being fixed. According to one embodiment of the invention, the second shaft comprises at least two clockwise wheel sets and at least two counter-clockwise wheel sets.

According to one embodiment of the invention, the guide tracks have a length of at least 10 cm, such as at least 20 cm, at least 30 cm, at least 40 cm or at least 50 cm.

According to one embodiment of the invention, the second shaft is at least partially within the first shaft.

According to one embodiment of the invention, the telescopic shaft further comprises a third shaft being movable in relation to the second shaft in the axial direction, at least one clockwise wheel set configured to exert force on the second shaft when the third shaft rotates clockwise about a longitudinal axis of the third shaft, at least one counter-clockwise wheel set configured to exert force on the second shaft when the third shaft rotates counter-clockwise about the longitudinal axis of the third shaft, each of the clockwise wheel set and the counter-clockwise wheel set comprising a plurality of wheels configured to roll against guide tracks on the second shaft, and each of the wheels being configured to always contribute in transmitting torque between the second and third shafts either when the third shaft rotates clockwise or when the third shaft rotates counter-clockwise . According to one embodiment of the invention, the third shaft is at least partially within the second shaft.

According to a second aspect of the invention, there is provided a parallel kinematics robot comprising a telescopic shaft according to any of the preceding embodiments. According to one embodiment of the invention, the telescopic shaft connects a base of the parallel kinematics robot to an end effector of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail with reference to the accompanying drawings, wherein figure la shows part of a telescopic shaft according to one embodiment of the invention, figure lb shows part of a telescopic shaft according to one embodiment of the invention, figure 2 shows a view along a longitudinal axis of a telescopic shaft of figure la, figure 3 illustrates rotational movements of wheels during operation of a telescopic shaft according to one embodiment of the invention, figure 4 shows a telescopic shaft according to one

embodiment of the invention, figure 5a shows a telescopic shaft according to one

embodiment of the invention, figure 5b shows a view along a longitudinal axis of a

telescopic shaft of figure 5a, and figure 6 shows a parallel kinematics robot with a

telescopic shaft according to one embodiment of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to figures la and lb, a telescopic shaft 10 according to one embodiment of the invention comprises a first shaft 20 and a second shaft 30. The second shaft 30 is partially within the first shaft 20 and movable in relation to the same in an axial direction 40. A plurality of wheels 50 is attached to the second shaft 30 and configured to roll against guide tracks 60 on the first shaft 20. A clockwise wheel set 70 comprising three wheels 50 symmetrically distributed about a longitudinal axis 90 of the second shaft 30 exerts force on the first shaft 20 when the second shaft 30 rotates clockwise 80 about the longitudinal axis 90, and a counter-clockwise wheel set 100 exerts force on the first shaft 20 when the second shaft 30 rotates counter-clockwise 110 about the longitudinal axis 90. The embodiment of figure lb comprises two clockwise wheel sets 70 and two counter ¬ clockwise wheel sets 100.

Referring to figures lb, 2 and 3, the wheels 50 are arranged on a wheel unit 120 that is part of the second shaft 30 and comprises wheel shafts 130 that are parallel to, but

slightly offset from, a radial direction 135 of the

longitudinal axis 90. The wheels 50 are arranged on bearings on the wheel shafts 130 and thereby rotate about wheel axes 140 that are parallel to, but slightly offset from, the radial direction 135, and immobile in relation to the second shaft 30. The clockwise and counter-clockwise wheel sets 70, 100 are identical, but due to the offset 150 they are configured to come into contact with different guide tracks 60 on the first shaft 20, and to transmit torque in

different directions. All the wheel shafts 130 are immobile in relation to the wheel unit 120, and the offset 150 is thereby fixed.

In contrast to the circulating rolling elements discussed in the background art section, of which only a part contributes in transmitting torque between two members in certain direction at a time, according to the present invention each of the wheels 50 is configured to always contribute in transmitting torque between the first and second shafts 20, 30 either when the second shaft 30 rotates clockwise 80 or when the second shaft 30 rotates counter-clockwise 110.

Referring to figure 4, a telescopic shaft 10 according to one embodiment of the invention comprises three support wheels 160 at an open end of the first shaft 20. The

function of the support wheels 160 is to give additional radial support to the second shaft 30 especially when the second shaft 30 is retracted deep within the first shaft 20. The first shaft 20 comprises a first fixture 170 for attachment to a base 210 of a parallel kinematics robot 200 (see figure 6) , and the second shaft 30 comprises a second fixture 180 for attachment to an end effector 220 of the parallel kinematics robot 200. The relative movement between the first and second shafts 20, 30 can be configured to be in the order of 10 cm to 70 cm, and the guide tracks 60 can thereby have a corresponding length in the order of 30 cm to 90 cm.

Referring to figures 5a and 5b, a telescopic shaft 10 according to one embodiment of the invention comprises a third shaft 190 partially within the second shaft 30 and movable in relation to the same in the axial direction 40. A plurality of wheels 50 is attached to the third shaft 190 and configured to roll against guide tracks 60 on the second shaft 30. A clockwise wheel set 70 comprising three wheels 50 symmetrically distributed about the longitudinal axis 90 exerts force on the second shaft 30 when the third shaft 190 rotates clockwise 80 about the longitudinal axis 90, and a counter-clockwise wheel set 100 exerts force on the second shaft 30 when the third shaft 190 rotates counter-clockwise 110 about the longitudinal axis 90. The guide tracks 60 of the second shaft 30 are identical with those of the first shaft 20, and the wheels 50 and wheel axes 140 of the third shaft 190 are identical with those of the second shaft 30. Referring to figure 6, the telescopic shaft 10 is configured to connect a base 210 of a parallel kinematics robot 200 to an end effector 220 of the same.

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.