Rob Dobson / SCARA_Arms

Calculations for a Dual-Arm SCARA robot Computes the shoulder angles to make the robot move to an XY position Also the reverse calculation - mainly useful as a cross-check

Description of a Dual-Arm SCARA robot (more info at http://robdobson.com/scara-arm-calculations)

The two arms of the robot are akin to two human arms with the hands permanently clasped together The arms are always in the same plane (generally horizontal) and the hands hold a stick (also in the same plane) On the end of the stick is the tool (pen/actuayor/nozzle/laser etc)

The measurements required to describe a Dual-Arm SCARA robot of the kind described above are: 1) Distance between shoulders 2) Distance from shoulder to elbow 3) Distance from elbow to hand 4) Distance from hand to tool (length of stick holding the tool)

Example Usage

Setup calculation double betweenShouldersMM = 320; double shoulderToElbowMM = 138; double elbowToHandMM = 307; double handToToolMM = 22.5; ScaraArms scaraArms(betweenShouldersMM, shoulderToElbowMM, elbowToHandMM, handToToolMM);

Compute the angles at the shoulders given the required XY position of the tool in radians double requiredX = 200; double requiredY = 180; double theta1, theta2; scaraArms.ConvertXYtoScara(requiredX, requiredY, theta1, theta2);

Show result printf("Angles required: left (from 3 O'Clock counter-clockwise) %f and right (from 9 O'Clock clockwise) %f", theta1, theta2);

ScaraArms.h@0:9a3fc5ff8de3, 2015-05-15 (annotated)

Committer:
Bobty
Date:
Fri May 15 08:50:58 2015 +0000
Revision:
0:9a3fc5ff8de3
Initial revision

Who changed what in which revision?

UserRevisionLine numberNew contents of line
Bobty 0:9a3fc5ff8de3 1 // SCARA_Arms library
Bobty 0:9a3fc5ff8de3 2 // Code to compute the shoulder angles required to move a Dual-Arm SCARA robot to required x,y position
Bobty 0:9a3fc5ff8de3 3 // More information at http://robdobson.com/scara-arm-calculations
Bobty 0:9a3fc5ff8de3 4 // Copyright (C) Rob Dobson 2013-2015, MIT License
Bobty 0:9a3fc5ff8de3 5
Bobty 0:9a3fc5ff8de3 6 #ifndef SCARAARMS_H
Bobty 0:9a3fc5ff8de3 7 #define SCARAARMS_H
Bobty 0:9a3fc5ff8de3 8
Bobty 0:9a3fc5ff8de3 9 // Description of a Dual-Arm SCARA robot
Bobty 0:9a3fc5ff8de3 10 // The two arms of the robot are akin to two human arms with the hands permanently clasped together
Bobty 0:9a3fc5ff8de3 11 // The arms are always in the same plane (generally horizontal) and the hands hold a stick (also in the same plane)
Bobty 0:9a3fc5ff8de3 12 // On the end of the stick is the tool (pen/actuayor/nozzle/laser etc)
Bobty 0:9a3fc5ff8de3 13
Bobty 0:9a3fc5ff8de3 14 class ScaraArms
Bobty 0:9a3fc5ff8de3 15 {
Bobty 0:9a3fc5ff8de3 16 public:
Bobty 0:9a3fc5ff8de3 17 // Constructor
Bobty 0:9a3fc5ff8de3 18 // The measurements required to describe a Dual-Arm SCARA robot of the kind described above are:
Bobty 0:9a3fc5ff8de3 19 // 1) Distance between shoulders
Bobty 0:9a3fc5ff8de3 20 // 2) Distance from shoulder to elbow
Bobty 0:9a3fc5ff8de3 21 // 3) Distance from elbow to hand
Bobty 0:9a3fc5ff8de3 22 // 4) Distance from hand to tool (length of stick holding the tool)
Bobty 0:9a3fc5ff8de3 23 ScaraArms(double betweenShouldersMM, double shoulderToElbowMM, double elbowToHandMM, double handToToolMM);
Bobty 0:9a3fc5ff8de3 24
Bobty 0:9a3fc5ff8de3 25 // Compute the angles at the shoulders given the required XY position of the tool in radians
Bobty 0:9a3fc5ff8de3 26 // Note that the way the angles are measured is that theta1 (the left arm angle) is measured counter-clockwise from 3 O'Clock
Bobty 0:9a3fc5ff8de3 27 // theta2 (the right arm angle) is measured clockwise from 9 O'Clock
Bobty 0:9a3fc5ff8de3 28 // To calculate both clockwise from 9 O'Clock use PI-theta2
Bobty 0:9a3fc5ff8de3 29 // To convert the angles to degrees multiply by 180/PI
Bobty 0:9a3fc5ff8de3 30 // The XY position has it's origin (0,0) at the left shoulder
Bobty 0:9a3fc5ff8de3 31 void ConvertXYtoScara(double x, double y, double &theta1, double &theta2);
Bobty 0:9a3fc5ff8de3 32
Bobty 0:9a3fc5ff8de3 33 // Compute the XY position of the tool given the angles at the shoulders
Bobty 0:9a3fc5ff8de3 34 // See the comments above for the reverse calculation concerning the way the angles are measured and the origin
Bobty 0:9a3fc5ff8de3 35 // of the XY coordinates
Bobty 0:9a3fc5ff8de3 36 // These calculations use a different mathematical model as the conversion in this direction is simpler and
Bobty 0:9a3fc5ff8de3 37 // it provides a useful cross check
Bobty 0:9a3fc5ff8de3 38 void ConvertScaratoXY(double theta1, double theta2, double &x, double &y);
Bobty 0:9a3fc5ff8de3 39
Bobty 0:9a3fc5ff8de3 40 private:
Bobty 0:9a3fc5ff8de3 41 double _betweenShouldersMM;
Bobty 0:9a3fc5ff8de3 42 double _shoulderToElbowMM;
Bobty 0:9a3fc5ff8de3 43 double _elbowToHandMM;
Bobty 0:9a3fc5ff8de3 44 double _handToToolMM;
Bobty 0:9a3fc5ff8de3 45 };
Bobty 0:9a3fc5ff8de3 46
Bobty 0:9a3fc5ff8de3 47 #endif