GRIPPER FOR SPOOLS

Abstract

The invention relates to a gripper (100) for finding, clamping and releasing spools (120) having a circular grip part (122) such as a flange or a bore hole as well as a method to operate such gripper. The gripper (100) comprises a driveable clamp (102) that is provided with a scanning system (106) comprising presence-absence detectors (108) that detect the presence of the absence of the circular grip part (122). The gripper (100) is slowly moved over the flange of the spool and by means of the detectors (108) and some calculation the centre of the grip part (122) is identified followed by the gripping of the spool. The gripper (100) has the advantage that no back-and-forth movement is needed in order to locate the circular grip part (122).

Claims

1. A gripper for finding, clamping and releasing a spool with a circular grip part comprising (a) a driveable clamp for clamping and releasing said grip part on demand, said clamp having a reference axis, said reference axis coinciding with the axis of the spool when clamped, said clamp having a clamp size configured to the diameter of the circular grip part of the spool; (b) a scanning system for identifying the axis of the spool characterized in that said scanning system comprises two or more sensors organized equidistant along a line, said two or more sensors for sensing in a direction parallel to said reference axis the presence of the spool, said reference axis defining a reference plane perpendicular to said reference axis, wherein the distance between any two adjacent sensors is less than the clamp size.

2. The gripper of claim 1 wherein the distance between any two adjacent sensors is between one quarter and three quarters of the clamp size.

3. The gripper of claim 1 wherein said reference axis is situated on the perpendicular bisector between two adjacent sensors in the reference plane, said two adjacent sensors being closest to the reference axis.

4. The gripper of claim 1 wherein said reference axis is situated on the perpendicular to said line at one sensor.

5. The gripper according to claim 1 wherein the perpendicular distance in the reference plane between said reference axis and said line is less than the clamp size.

6. The gripper of claim 5 wherein the perpendicular distance in the reference plane between said reference axis and said line is more than half the clamp size.

7. The gripper according to claim 1 wherein the circular grip part is the bore hole of a spool, and said clamp is a shaft for insertion and holding in the bore hole, said clamp size corresponding to the diameter of said shaft

8. The gripper according to claim 1 wherein the circular grip part is the flange of the spool and said clamp is a flange clamp for clamping and holding at the flange, said clamp size corresponding to the diameter of said flange.

9. A method for handling a spool by means of a gripper according to claim 1, said gripper having a reference axis, the spool having a circular grip part, said method comprising the steps of: (a) Positioning the gripper in the vicinity of the spool, such that said reference axis is parallel to the axis of the spool to be gripped; (b) Providing a local controller for controlling the movement of said gripper; (c) Input the diameter of the circular grip part to said local controller from a global controller; (d) Moving said gripper in said reference plane with said two or more sensors ahead of said reference axis while recording the travelled distance over a limited travel length; (e) Detect a first changeover in the presence of the circular grip part at a first sensor and record the travelled distance at that changeover as a first point; (e) Detect a second changeover in the presence of the circular grip part at a second sensor and record the travelled distance at that changeover as a second point; (f) Based on said first and second point and said diameter: calculate the centre position of said circular grip part in said reference plane; (g) Move said reference axis to said calculated centre position; (h) Clamp and hold the spool by the circular grip part.

10. The method according to claim 9 wherein the first and second sensor are adjacent sensors.

11. The method according to claim 9 wherein the first and second sensor are one and the same.

12. A method for handling a spool by means of a gripper according to claim 1, said gripper having a reference axis, the spool having a circular grip part, said method comprising the steps of: (a) Positioning the gripper in the vicinity of the spool, such that said reference axis is parallel to the axis of the spool to be gripped; (b) Providing a local controller for controlling the movement of said gripper; (d) Moving said gripper in said reference plane with said two or more sensors ahead of said reference axis while recording the travelled distance over a limited travel length; (e) Detect a first changeover in the presence of the circular grip part at a first sensor and record the travelled distance at that changeover as a first point; (e) Detect a second changeover in the presence of the circular grip part at a second sensor and record the travelled distance at said second changeover as a second point; (e) Detect a third changeover in the presence of the circular grip part at a third sensor and record the travelled distance at said third changeover as a third point; (f) Based on said first, second and third point: calculate the centre position of said circular grip part in said reference plane; (g) Move said reference axis to said calculated centre position; (h) Clamp and hold the spool by the circular grip part.

13. The method according to claim 12 wherein said third sensor is either said first or said second sensor.

14. The method of claim 12 wherein after step (b) the step (c) is introduced: (c) Input the diameter of the circular grip part to said local controller from a global controller; and after step (f) step (f) is introduced: (f) calculate the diameter of the circular grip part and emit an alarm when the calculated and input values differ by more than 5%;

15. The method according to claim 9, wherein in case step (d) ends at the limited travel length the gripper is repositioned to its original position and shifted along the line of said sensors over a shift that is equal to the distance between adjacent sensors times the number of sensors and the step of (d) is repeated.

16. The method according to claim 9 wherein said limited travel length ends when the gripper has travelled the diameter of the circular grip part after the detection of the first changeover.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0051] FIG. 1 shows a general overview of the gripper according the invention in its most general form;

[0052] FIGS. 2a and 2b illustrates the first and second case of the first mode of operation;

[0053] FIGS. 3a and 3b illustrate the first and second case of the second mode of operation

[0054] FIG. 4 shows an actual embodiment of the gripper;

[0055] FIG. 5 shows how the gripper aligns with the spool.

[0056] Like parts over different figures have the same unit and tens number while the hundred number refers to the figure number.

MODE(S) FOR CARRYING OUT THE INVENTION

[0057] FIG. 1 shows a view from above of a general embodiment of the gripper 100. The gripper comprises a driveable clamp 102 that is mounted on an arm of a robot or automatically guided vehicle or similar device (not shown). The clamp 102 has a reference axis indicated with 104 that is in this case perpendicular to the plane of the sheet. The spool to be gripped is shown as 120 and has a circular grip part 122 that is in this case the bore hole of the spool 120. The circular grip part 122 has a diameter indicated with D. The clamp sizecorresponding to the diameter of the clamp 102is thus slightly less than D in order to allow insertion of the clamp into the bore hole. The gripper has a scanning system 106 comprising four sensors indicated with 108, 108, 108, 108 on a line 110. The sensors are separated from one another by a distance . The distance A is just less than D/2 for example 0.45D. The sensors sense the presence or absence of the spool body 120 in a direction parallel to the reference axis 104. The sensors are for example photoelectric presence-absence sensors based on reflection of light such as the LR-W series of Keyence.

[0058] The reference axis 104 is situated on the perpendicular bisector 112 between the two adjacent sensors 108 and 108. The perpendicular distance between the reference axis 104 and the line of sensors 110 is indicated with d. d is less than the diameter D but larger than D/2. During use the gripper scans for the presence of the circular grip part in the direction {right arrow over (v)} in parallel with the perpendicular bisector 112.

[0059] The first mode of operation of the gripper is illustrated in FIGS. 2a and 2b. Here the case of two sensors (N=2) is used to illustrate the working. A fixed reference frame is constructed with the X-axis along the line of sensors 210 and the Y-axis along the perpendicular bisector 212. y coordinates increase with the movement of the gripper {right arrow over (v)}. Hence, the first sensor 208 is initially situated at coordinates (/2, 0) and the second sensor at (+/2, 0). The reference axis 204 is initially situated at (0, d). As the gripper moves, the X-coordinates remain invariant, but the Y-coordinates increase. When the local controller takes over, the Y-coordinate is zeroed.

[0060] First the gripper is positioned in the vicinity of the spool and the reference axis 204 is brought in alignment with the axis of the spool under the control of the global controller. The global controller will also indicate a direction of movement {right arrow over (v)} to the local controller. The diameter D of the circular grip part is transmitted to the local controller by the global controller. Then control of movement is surrendered to the local controller. The radius of the circular grip part is indicated with R in FIG. 2 and is equal to D/2.

[0061] Then the local controller moves the gripper in the direction {right arrow over (v)} at slow speed in the reference plane with the two sensors 208 and 208 ahead of the reference axis 204. At (x.sub.1,y.sub.1) a first changeoverfrom the spool flange to the bore holeis detected by sensor 208 defining a first point at (/2,y.sub.1) wherein y.sub.1 is the distance travelled along direction {right arrow over (v)}. The scan continues until the second sensor 208 detects a second changeoveragain from the spool flange to the bore holeat the point (x.sub.2,y.sub.2). The second point thus has coordinates (+/2,y.sub.2).

[0062] Now the local controller calculates the position of the centre C of the circular grip part as follows:

[0063] First the distance a between the first and second point is calculated:

a={square root over ((x.sub.2x.sub.1).sup.2+(y.sub.2y.sub.1).sup.2)}={square root over (.sup.2+(y.sub.2y.sub.1).sup.2)}

[0064] Then the quantity is calculated

[00001]$A=\sqrt{\frac{D^2}{a^2}-1}$

[0065] Now the two possible solutions for the centre C have coordinates (x.sub.0,y.sub.0):

x.sub.0=[(x.sub.2+x.sub.1)A(y.sub.2y.sub.1)] and y.sub.0=[(y.sub.2+y.sub.1)A(x.sub.2x.sub.1)]

[0066] In this case the solution with the highest y.sub.0 must be chosen as the other solutionindicated with 222 in FIG. 2awould not be commensurate with the order of first and second detected point resulting in:

x.sub.0=[A(y.sub.2y.sub.1)] and y.sub.0=[(y.sub.2+y.sub.1)A(x.sub.2x.sub.1)]

[0067] Note that if 208 would detect the first changeover the sign of x.sub.0 must be reversed.

[0068] In the second case of the first mode of operation one of the sensors 208 detects a first changeoverfrom spool flange to bore holebut the same detector 208 also detects a second changeoverfrom bore hole to flangewhile the other sensor 208 does not detect any changeover. In that case the coordinates of (x.sub.1,y.sub.1) become (/2, y.sub.1) and of (x.sub.2,y.sub.2) are (/2, y.sub.2).

[0069] Hence the formulas simplify to:

a={square root over ((x.sub.2x.sub.1).sup.2+(y.sub.2y.sub.1).sup.2)}=|y.sub.2y.sub.1|

and

x.sub.0=[A(y.sub.2y.sub.1)] and y.sub.0=[(y.sub.2+y.sub.1)]

[0070] wherein the leftmost solution must be chosen as the alternative solutionindicated with 222 in FIG. 2bwould have been detected by sensor 208. Mutatis mutandis the reasoning and formulas also holds when 208 only detects two changeovers when passing to the left of the centre point C but then the other solution must be chosen resulting in:

x.sub.0=[+A(y.sub.2y.sub.1)] and y.sub.0=[(y.sub.2+y.sub.1)]

[0071] The position of the centre of the circular grip part is thus known in the fixed reference frame. Now the reference axis 204 of the clamp 202 still has to be moved to the correct position. As at the moment of the detection of the second changeover, the reference axis is situated at (0, y.sub.2d) only a translation from there to (x.sub.0, y.sub.0) must be completed or a final translation of (x.sub.0,y.sub.0y.sub.2+d).

[0072] Note that in this procedure the total scan width W is equal to A+2R with the proviso that A is smaller than R.

[0073] FIGS. 3a and 3b illustrate the second mode of operation wherein the diameter of the circular grip part is initially not known. The method is illustrated with three sensors (N=3) although it equally well works with two sensors. The X-axis of the fixed reference frame is taken along the line of the sensors. The zero of the X-axis is taken at the perpendicular through the reference axis 304. The reference axis is thus situated at (0,d). The Y-axis is parallel to the movement direction {right arrow over (v)} and is zeroed at the start of the scan.

[0074] When scanning it may occur that first the sensor 308 notices a changeover thereby recording the point (x.sub.1,y.sub.1) followed by the sensor 308 that records point (x.sub.2,y.sub.2) and finally by sensor 308 that records point (x.sub.3,y.sub.3). As soon as three changeovers have been detected, the position of the centre C (x.sub.0,y.sub.0) of the circular part is calculated with the formulas:

[00002]$\mathrm{Det}=\left|\begin{array}{ccc}{x}_1& y_1& 1\\ x_2& y_2& 1\\ x_3& y_3& 1\end{array}\right|,r_1^2=x_1^2+y_1^2,r_2^2=x_2^2+y_2^2,r_3^2=x_3^2+y_3^2$$x_0=\underset{2.Math..Math.\mathrm{Det}}{\underset{\_}{\left|\begin{array}{ccc}{r}_1^2& y_1& 1\\ r_2^2& y_2& 1\\ r_3^2& y_3& 1\end{array}\right|}}.Math..Math.y_0=\underset{2.Math..Math.\mathrm{Det}}{\underset{\_}{\left|\begin{array}{ccc}{x}_1& r_1^2& 1\\ x_2& r_2^2& 1\\ x_3& r_3^2& 1\end{array}\right|}}$

[0075] In this case there is only one possible solution for C.

[0076] Alternatively the situation as depicted in FIG. 3b may occur. There the first changeover is detected by sensor 308 thereby defining the first point (x.sub.1,y.sub.1). Thereafter the sensor 308 detects the two changeovers at (x.sub.2,y.sub.2) and at (x.sub.3,y.sub.3). As soon as these three points are known the position of the centre point C with coordinates (x.sub.0,y.sub.0) can be calculated with the same formulas as above. Again there is only one possible solution for C.

[0077] At the moment three changeovers have been detected, the reference axis 304 is at position (0, y.sub.3d). The gripper than only has to translate over the vector (x.sub.0,y.sub.0y.sub.3+d) to position the reference axis 304 in line with the centre point C. When positioned the gripper shaft can be introduced into the bore hole by translation along the reference axis.

[0078] As now the centre point C of the circular grip part is known, the radius and the diameter D can easily be calculated as the distance between any one of the recorded points and C. The result can be compared to the diameter of the circular grip part obtained from the global controller in order to verify whether the correct spool is present.

[0079] If none or only two changeovers have been detected when the limited travel length is reached, the procedure is repeated after having repositioned the gripper to its starting position and having it shifted in the direction away from the sensors that have not detected any changeover over a length that is equal to the N. A reasonable travel limit length is reached when after a first changeover detection the scan is continued for a length equal to the diameter of the circular grip part. If that diameter is not known, then a maximum diameter of all circular grip parts used within the fracture can be used as a limit.

[0080] FIG. 4 shows an actual implementation of the gripper 400 with all the various components: the reference axis 404 is indicated with the driveable clamp 402. The clamp is provided with claws 420 that engage with an internal groove in the bore hole of the spool. The claws 420 can be retracted in order to release spool upon command. Two laser presence-absence detectors 408 and 408 are indicated thatduring movement of the gripperprecede the clamp 402.

[0081] FIG. 5 shows the alignment of the clamp 500 with the spool 520 when the reference axis is in line with the axis of the spool prior to the gripping of the spool.