Move an arm

Viam exposes three ways to command an arm. Three questions sort them:

  1. What do you know about the destination? A Cartesian target (a pose in space) calls for the motion service. A specific joint configuration calls for direct joint commands.
  2. Does the shape of the motion matter, or only the endpoint? If you need a straight line, a fixed orientation, or any other rule about the path itself, you need constraints.
  3. Do you want obstacle avoidance and IK picked for you, or fine manual control? The motion service handles both; direct joint commands skip both.
PatternInputObstacle avoidancePath-shape controlWhen to pick
Move to a poseCartesian targetYesNoYou know where the end effector needs to go and want the planner to figure out how.
Move with constraintsCartesian target + rulesYesYesThe shape of the motion matters (straight-line tool path, level end effector).
Move by joint positionsJoint anglesNoDirectYou know the joint angles, need predictable motion between known configurations, or want to avoid the planner picking an unexpected IK solution.

For the four constraint types the planner enforces, see Configure motion constraints.

Pick and place

Pick-and-place is the point where motion planning, vision, and gripper control meet. Each service works on its own, but the failure modes that matter most (the gripper closing on air, a depth estimate that crashes the arm into the table) only appear when all three run together.

The workflow splits into two stages so each can be developed and debugged independently:

  • Pick covers detection, approach, and grasp. The arm moves to a pre-grasp pose above the object, descends, closes the gripper on the object, and lifts.
  • Place covers transport and release. The arm moves the grasped object to a target location, descends, opens the gripper, and retreats.

Both stages reuse the obstacle definitions and geometry-attachment patterns from Obstacles and the arm-motion patterns from the table above.

How-tos

Configure constraints

Restrict how the arm moves between poses using linear, orientation, and collision constraints.

Move an arm to a pose

Use the motion service to move a robot arm to a position in 3D space.

Move with constraints

Move an arm along a straight line or with a fixed orientation using motion constraints.

Move by joint positions

Command an arm directly in joint space using MoveToJointPositions and MoveThroughJointPositions, bypassing the motion planner.

Pick an object

Detect, localize, and grasp an object with a robot arm and gripper.

Place an object

Move a grasped object to a target location and release it.