WO1998058775A1

WO1998058775A1 - A device for detecting the angular position of a rotary member in a numerically-controlled angular positioning system, particularly a member of a manipulator robot, and a robot incorporating the device

Info

Publication number: WO1998058775A1
Application number: PCT/EP1998/003741
Authority: WO
Inventors: Antonio Codatto
Original assignee: Antonio Codatto
Priority date: 1997-06-23
Filing date: 1998-06-19
Publication date: 1998-12-30
Also published as: ITTO970547A0; ITTO970547A1; IT1293381B1

Abstract

A rotary encoder (126) is used for detecting the angular position of a rotary member (50). A set of teeth (106) is fixed rigidly to the rotary member (50). The encoder (126) is coupled to a shaft (118) having a sprocket (120) meshed with the set of teeth (106).

Description

A device for detectincr the ancrular position of a rotary member in a numerically-controlled angular positioning system, particularly a member of a manipulator robot, and a robot incorporating the device

The present invention relates to a device for detecting the angular position of a rotary member according to the preamble to Claim 1.

The invention has been devised for application to a manipulator robot which is to form part of a panelling machine, that is, a machine comprising the robot and a bending press for processing sheet-metal panels.

It may, however, be used for detecting the angular position of any rotary member for which maximum accuracy of angular positioning is required.

Numerically-controlled machines are designed, amongst other things, to achieve positioning with maximum accuracy.

In general, a numerical control system comprises, on the one hand, a stepping electric motor, and on the other hand, a position detector which serves to send to the control system a feedback signal for the purposes of the angular positioning of the rotary member controlled by the motor.

The preferred angular position detector is constituted by a rotary encoder.

In the prior art, rotary encoders were connected directly to the motor shaft .

When the motor shaft and the rotary member controlled thereby are interconnected by a mechanical transmission, the detection of the angular position of the motor shaft by means of the encoder does not take account of play in the transmission so that the detection of the angular position of the rotary member suffers from an error which, in certain applications, has a highly adverse effect on accuracy.

The object of the present invention is to provide a detection device according to the preamble to Claim 1 which does not suffer from the aforementioned error.

According to the invention, this object is achieved by means of a detection device as claimed.

By virtue of the solution claimed, to favour accuracy, the rotary encoder detects the angular position of the rotary member directly, and not that of the motor shaft.

The invention also relates to a robot, particularly a manipulator robot, incorporating the device claimed.

The invention will be understood more clearly from a reading of the following detailed description, given with reference to the appended drawings, provided by way of non-limiting example, in which:

Figure 1 is a side elevational view of a manipulator robot with an arm,

Figure 2 is a sectioned elevational view showing, on an enlarged scale, a unit, indicated II in Figure 1, which is disposed at the free end of the robot arm,

Figure 3 is a partial section taken in the vertical plane indicated III-III in Figure 1, on an enlarged scale,

Figure 4 is a partial elevational view taken on the arrow IV of Figure 2, Figure 5 is a transverse section taken in the plane indicated V-V in Figure 2,

Figure 6 is a partially-sectioned, partial side elevational view taken on the arrow VI of Figure 3 , and

Figure 7 is a partial transverse section taken in the plane indicated VII-VII in Figure 3.

With reference to Figure 1, a manipulator robot comprises a telescopic arm 10 which can swing about a vertical axis A.

At the end of the telescopic arm 10 there is a working head 12 which, in the embodiment in question, is in the form of a gripping head provided with suction cups for the manipulation of sheet-metal panels.

The telescopic arm 10 is supported by a hollow pillar 14 rotatable about the vertical axis A, as indicated by the double arrow Fl .

The pillar 14 in turn is supported by a fixed base 16.

A hollow portion 18 of the arm 10 is mounted on the top of the pillar 14 so as to be able to pivot about a horizontal axis B, as indicated by the double arrow F2.

A movable portion 20 is slidable telescopically in the hollow portion 18, as indicated by the double arrow F3.

The arm 10 is moved about the horizontal axis B by a numerically-controlled electric motor 22 by means of a threaded-shaft transmission the shaft of which is indicated 24. The telescopic movements of the movable portion 20 are brought about by a numerically-controlled motor 26 by means of a threaded-shaft transmission, not shown in detail.

At its free end, the movable portion 20 of the arm 10 carries a first element 28 rotatable about a substantially horizontal axis C by means of a numerically-controlled electric motor 30, as indicated by the double arrow F4.

The first element 28 in turn supports a second element 32 pivotable about a horizontal axis D, as indicated by the double arrow F5.

The angular pivoting of the second element 32 is brought about by a numerically-controlled electric motor 34 and by means of a threaded-shaft transmission the shaft of which is indicated 36.

The head 12 is mounted for rotating, as indicated by the double arrow F6 , on a free end of the second element 32.

The axis of rotation of the head 12 is indicated E.

For further details relating to the characteristics of the robot of Figure 1 and to its field of application as a manipulator in a panelling machine, reference should be made to a PCT patent application for "A device for pivoting a swinging arm, such as an arm of a manipulator robot, about a vertical axis, and a manipulator robot including the device" filed by the Applicant on the same date.

With reference to Figure 2, the head 12 comprises a bar 38 which carries two sets of suction cups 40.

The bar 38 is fixed to an attachment 42 with an internal, conical, "Morse" -type seat 44. The corresponding cone of a rotary spindle 46, rotatable about the axis E, is fitted in the seat 44, the spindle having an internal duct 48 for drawing in the air from the suction cups 40.

The spindle 46 is fixed to the lower portion of a rotary member 50.

A cavity 52 inside the rotary member 50 communicates, by means of radial ducts 54 and in a manner not shown, with a vacuum source .

The rotary member 50 is mounted for rotating about the axis E in a hollow support body 56 fixed rigidly to a bracket 58 which forms part of the second element 32 of Figure 1.

A reduction unit 60, mounted in an upper portion of the hollow body 56, has a driven member 62 in the form of a hub fixed rigidly to the rotary member 50.

A driving member 64, in the form of a hub, of the reduction unit 60 is keyed to a small shaft 66 rotatable about the same axis E.

The reduction unit 60 is preferably of the Cyclo type described and illustrated in the Applicant's PCT patent application of the same date, already mentioned.

The bracket 58 carries a numerically-controlled electric motor 68 to the output shaft 70 of which a toothed pulley 72 is keyed. A toothed pulley 74 of the same diameter and with the same number of teeth is keyed to the small shaft 66.

The two pulleys 72, 74 are interconnected by a toothed belt 76 which transmits the motion of the shaft 70 of the motor 68 to the driving member 64 of the reduction unit 60, with a ratio of 1:1. With the use of a Cyclo-type reduction unit 60, a high reduction ratio which may be equal to 1/179 is preferably used.

The further details which can be seen in Figure 2 will be described further below with reference to this drawing and to Figures 4 and 5.

Reference will now be made to Figure 3 to describe the structure for supporting and rotating the hollow pillar 14 about the vertical axis A.

A fixed structure 78 which is substantially C-shaped in cross-section is fixed to the base 16.

The hollow pillar 14 is supported by a rotatable platform 80 which comprises an annular peripheral portion 82 bearing on the movable ring of a radial-axial bearing 83.

The rotatable platform 80 also comprises a spoke which extends in the space defined by the C-shape of the fixed structure 78 and which terminates in a flange-like portion 84 centred on the axis A.

The fixed structure 78 supports a mechanical transmission constituted by a pair of planetary reduction units, preferably of the Cyclo type .

A first, main reduction unit is generally indicated 86 and a second, secondary reduction unit is generally indicated 88.

For all details of the reduction units 86 and 88 and for further details of the structure shown in Figure 3, reference should be made to the Applicant's PCT patent application, already mentioned, filed on the same date. A support 90 which is substantially Ω-shaped in diametral section is fitted on the main reduction unit 86.

A numerically-controlled, reversible electric motor 92 has its casing fixed to the support 90 and its shaft, which is centred on the axis A, is coupled to the driving members 94, 96 of both reduction units 86, 88.

The driven members 98, 100 of both reduction units 86, 88 are fixed to the flange-like portion 84 of the rotatable platform 80.

The use of two planetary reduction units 86, 88 which work mechanically in parallel enables the angular play between the motor shaft 92 and the pillar 14 to be cancelled out by means of an adjustment system described in the Applicant's PCT patent application already mentioned, filed on the same date.

The means which, both in the case of the rotary member 50 of Figure 2 , and in the case of the rotary member constituted by the rotatable platform 80 of Figure 3, enable the angular position of these members to be detected with maximum accuracy will now be described.

Since these means are substantially identical both in the case of Figure 2 and in that of Figure 3 , the same reference numerals will be used as far as possible in the description thereof .

For the case of Figure 2 , reference will be made to Figures 4 and 5, and for the case of Figure 3, reference will be made to Figures 6 and 7.

Figures 4 and 5, on the one hand, and Figures 6 and 7, on the other hand, have been placed side by side on the same sheet for the reader ' s convenience . A toothed ring 104 centred on the axis E is fixed to the rotary member 80 of Figure 2.

A ring with peripheral teeth and also indicated 104 is fixed to the rotary platform 80 of Figure 3.

The sets of teeth of these toothed rings are indicated 106.

A support block 108 is fixed to a peripheral region of the fixed body 56 of Figure 2 and of the fixed structure 78 of Figure 3 and a forked bracket 110 in turn is fixed thereto.

A movable element in the form of a rocker-like lever 112 is mounted in the bracket 110 for pivoting on a vertical pin 114.

A small vertical shaft 118 is mounted in one arm 116 of the lever 112 and a sprocket 120, keyed thereto, is kept meshed with the set of teeth 106.

In the case of Figures 6 and 7 , an annular plate 122 supported in a position raised from the base 16 (Figure 3) carries a sleeve-like support 124 on which a rotary encoder 126 with a vertical axis aligned with the small shaft 118 is fixed as an angular position detector.

In the case of Figure 2, the encoder 126 is supported by the bracket 58, again in alignment with the small shaft 118.

In both cases, the shaft of the encoder 126 is connected to the small shaft 118 of the sprocket 120 by means of flexible couplings 128.

As will be understood, to favour accuracy, both in the case of Figures 4 and 5 and in the case of Figures 6 and 7 , the encoder 126 detects the position of the rotary member 50 of Figure 2, or of the pillar 14 of Figure 3 directly, and not that of the shaft of the motor 68 of Figure 2 or of the motor 92 of Figure 3.

In order further to increase the accuracy of the detection of the angular position, another arm 130 of the rocker-like lever 112 contains a sliding pin 132 which reacts against the block 108 under the force of resilient means constituted by a helical spring 134.

The spring 134 keeps the sprocket 120 in engagement with the set of teeth 106 without play for even greater accuracy in the detection of the angular position of the rotary member 50 and of the head 12 of Figure 2 or of the pillar 14 of Figure 3.

Figures 5 and 7 show a means for detecting a "zero" position of the rotary member 50 and of the respective head 12 of Figure 2, or of the pillar 14 and of the respective arm 10 of Figures 1 and 3.

The "zero" position, which is input into the numerical control system as a basic datum, may correspond, for example, to a certain orientation of the head 12 of Figure 2 , or to a certain orientation of the arm 10 of Figure 1.

A bracket 136 fixed on one side of the support body 56 of Figure 2 or of the fixed structure 78 of Figure 3 in turn carries a position detector 138 in the form of a proximity switch the sensitive end of which faces the set of teeth 106, in close proximity thereto.

A blind radial hole 140 corresponding to a "zero" position, is formed between two teeth of the set of teeth 106.

The presence of the hole 140 in front of the switch 138 causes a change in the state of the switch and the transmission of a corresponding signal to the numerical control system, or the interruption of the signal.

Claims

1. A device for detecting the angular position of a rotary member (50; 78) mounted on a support (56; 78) and rotated by a motor (68; 92) in a numerically-controlled angular positioning system, in which a rotary encoder (126) is used for detecting the angular position,

characterized in that it comprises a set of teeth (106) fixed rigidly to the rotary member (50, 78), and in that the encoder (126) is coupled to a shaft (118) having a sprocket (120) meshed with the set of teeth (106) .

2. A device according to Claim 1, characterized in that the sprocket (120) is supported by the support body (56; 78) by means of a movable element (112) incorporating resilient means (134) tending to eliminate the play between the teeth of the set of teeth (106) and the sprocket (120) .

3. A device according to Claim 2 , characterized in that the movable element is in the form of a lever (112) pivoting about a fulcrum (114) parallel to the axis of rotation (A; E) of the rotary member (50; 78) and of its set of teeth (106), and the sprocket (120) is carried by an arm (116) of the lever (112) .

4. A device according to Claim 3 , characterized in that the lever (112) is in the form of a rocker with two opposite arms of which one (116) carries the shaft (118) coupled to the encoder (126) and the other (130) is acted on by resilient means in the form of a helical compression spring (134) .

5. A device according to any one of the preceding claims, characterized in that it comprises a means for detecting a "zero" position of the rotary member (50; 78), the means being constituted by a proximity switch (138) having a sensitive end facing the set of teeth (106) , and in that a hole (140) to the presence of which the proximity switch (138) is sensitive, is formed between two teeth of the set of teeth (106) .

6. A robot, particularly a manipulator robot, incorporating a device according to any one of the preceding claims .