kins − kinematics definitions for LinuxCNC
loadrt trivkins (use for most cartesian machines)
loadrt lineardeltakins (see separate manpage)
Rather than exporting HAL pins and functions, these components provide the forward and inverse kinematics definitions for LinuxCNC.
− generalized trivial kinematics
Joint numbers are assigned sequentialy according to the axis letters specified with the coordinates= parameter.
coordinates= parameter is omitted, joint numbers are
assigned sequentially to every known axis letter
Example: loadrt trivkins
Assigns all axis letters to joint numbers in sequence:
a==joint3, b==joint4, c==joint5
u==joint6, v==joint7, w==joint8
Example: loadrt trivkins coordinates=xyz
Assigns: x==joint0, y==joint1, z==joint2
Example: loadrt trivkins coordinates=xz
Assigns: x==joint0, z==joint1
Example: loadrt trivkins coordinates=xyzy
Assigns: x==joint0, y0==joint1, z==joint2, y1==joint3
kinematics type is KINEMATICS_IDENTITY. Guis may
provide special features for configurations using this
default kinematics type. For instance, the axis gui
automatically handles joint and world mode operations so
that the distinctions between joints and axes are not
visible to the operator. This is feasible since there is an
exact correspondence between a joint number and its matching
The kinematics type can be set with the kinstype= parameter:
kinstype=1 for KINEMATICS_IDENTITY (default if kinstype= omitted)
kinstype=[b|B] for KINEMATICS_BOTH
kinstype=[f|F] for KINEMATICS_FORWARD_ONLY
kinstype=[i|I] for KINEMATICS_INVERSE_ONLY
Example: loadrt trivkins coordinates=xyz kinstype=b
Use kinstype=B (KINEMATICS_BOTH) for configurations that need to move joints independently (joint mode) or as coordinated (teleop) movements in world coordinates.
When using the axis gui with KINEMATICS_BOTH, the ’$’ key is used to toggle between joint and teleop (world) modes.
An axis letter
may be used more than once (duplicated) to assign
multiple joints to a single axis coordinate letter.
Example: coordinates=xyyzw kinstype=B
Assigns: x==joint0, y==joint1 AND joint2, z==joint3, w==joint4
The above example illustrates a gantry configuration that uses duplicated coordinate letters to indicate that two joints (joint1 and joint2) move a single axis (y). Using kinstype=B allows the configuration to be toggled between joint and world modes of operation. Homing configuration options are available to synchronize the final homing move for selected joints -- see the documentation for Homing Configuration.
NOTES for duplicated coordinates:
When duplicated coordinate letters are used, specifying KINEMATICS_BOTH (kinstype=B) allows a gui to support jogging of each individual joint in joint mode. Caution is required for machines where the movement of a single joint (in a set specified by a duplicated coordinate letter) can lead to gantry racking or other unwanted outcomes. When the kinstype= parameter is omitted, operation defaults to KINEMATICS_IDENTITY (kinstype=1) and a gui may allow jogging based upon a selected axis coordinate letter (or by a keyboard key) before homing is completed and the machine is still in joint mode. The joint selected will depend upon the gui implementation but typically only one of the multiple joints in the set will jog. Consequently, specifying KINEMATICS_BOTH is recommended as it enables support for unambiguous, independent jogging of each individual joint. Machines that implement homing for all joints (including the provisions for synchronizing the final homing move for multiple joints) may be homed at machine startup and automatically switch to world mode where per-coordinate jogging is available.
− CoreXY Kinematics
X = 0.5*(JOINT_0 + JOINT_1)
Y = 0.5*(JOINT_0 − JOINT_1)
Z = JOINT_2
[KINS]JOINTS= must specify 3 or more joints (maximum 9)
If enabled by the number of [KINS]JOINTS= specified, JOINT_3,4,5,6,7,8
correspond to coordinates A,B,C,U,V,W respectively.
− Hexapod Kinematics
Gives six degrees of freedom in position and orientation (XYZABC). The location of base and platform joints is defined by hal parameters. The forward kinematics iteration is controlled by hal pins.
Parameters describing the Nth joint’s coordinates.
Added to all joints Z coordinates to change the machine origin. Facilitates adjusting spindle position.
Parameters describing unit vectors of Nth joint’s axis. Used to calculate strut length correction for cardanic joints and non-captive actuators.
Lead of strut actuator screw, positive for the right-handed thread. Default is 0 (strut length correction disabled).
Current values of strut length correction for non-captive actuators with cardanic joints. genhexkins.convergence−criterion Minimum error value that ends iterations with converged solution.
Limit of iterations, if exceeded iterations stop with no convergence.
Maximum error value, if exceeded iterations stop with no convergence.
Number of iterations spent for the last forward kinematics solution.
Maximum number of iterations spent for a converged solution during current session.
TCP offset from platform origin along Z to implement RTCP function. To avoid joints jump change tool offset only when the platform is not tilted.
− generalized serial kinematics
Kinematics that can model a general serial-link manipulator with up to 6 angular joints.
use Denavit-Hartenberg definition for the joint and links.
The DH definitions are the ones used by John J Craig in
"Introduction to Robotics: Mechanics and Control"
The parameters for the manipulator are defined by hal pins.
Note that this uses a convention sometimes known as
"Modified DH Paremeters" and this must be borne in
mind when setting up the system.
Parameters describing the Nth joint’s geometry.
− 5-axis kinematics example
Kinematics for Chris Radek’s tabletop 5 axis mill named ’max’ with tilting head (B axis) and horizintal rotary mounted to the table (C axis). Provides UVW motion in the rotated coordinate system. The source file, maxkins.c, may be a useful starting point for other 5-axis systems.
− kinematics for puma typed robots
Kinematics for a puma-style robot with 6 joints
Describe the geometry of the robot
− kinematics for a rose engine using
a transverse, longitudinal, and rotary joint (3 joints)
− kinematics for a rotary delta machine
Rotary delta robot (3 Joints)
− Rotated Kinematics
The X and Y axes are rotated 45 degrees compared to the joints 0 and 1.
− kinematics for SCARA-type robots
Vertical distance from the ground plane to the center of the inner arm.
Horizontal distance between joint axis and joint axis, ie. the length of the inner arm.
Vertical distance from the center of the inner arm to the center of the outer arm. May be positive or negative depending on the structure of the robot.
Horizontal distance between joint axis and joint axis, ie. the length of the outer arm.
Vertical distance from the end effector to the tooltip. Positive means the tooltip is lower than the end effector, and is the normal case.
Horizontal distance from the centerline of the end effector (and the joints 2 and 3 axis) and the tooltip. Zero means the tooltip is on the centerline. Non-zero values should be positive, if negative they introduce a 180 degree offset on the value of joint.
− Tripod Kinematics
The joints represent the distance of the controlled point from three predefined locations (the motors), giving three degrees of freedom in position (XYZ)
The location of the three motors is (0,0), (Bx,0), and (Cx,Cy)
− 5 Axis mill (Table Rotary/Tilting)
Tilting table (A) and horizontal rotary mounted tothe table (C) (5 Joints)
− 5 Axis mill (Table Rotary/Tilting)
Tilting table (B) and horizontal rotary mounted to table (C axis) (5 Joints)
− 5 Axis bridge mill
XYZBC (5 Joints)
Kinematics section in the LinuxCNC documentation