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Moving an Arm
Description: This tutorial shows step-by-step how to move an ArbotiX-based arm controlled by the simple arm server.Tutorial Level: INTERMEDIATE
Prerequisites
This tutorial assumes that you have an ArbotiX/Dynamixel-based arm, with a trajectory controller and URDF properly configured.
Overview
The simple arm server allows you to move an arm through a series of goals. The MoveArm request contains a header and an array of ArmAction goals:
std_msgs/Header header ArmAction[] goals
The header is used to specify the frame_id of the goals, while each ArmAction goal consists of several fields:
byte type # move the arm or the gripper? geometry_msgs/Pose goal # goal for an arm float64 command # goal for a gripper duration move_time
Arm Position Goals
Most goals will move the arm to a position. In this case, we fill out the pose goal and set type to MOVE_ARM, a constant defined in the ArmAction message.
Gripper Goals
Goals can also set the commanded position of the gripper. In this case, we set type equal to MOVE_GRIPPER and set the command field of the request.
Example Code
The multi_waypoint_test.py example in simple_arm_server shows how to move the arm through a small trajectory, picking up a block, and then dropping it in a different location:
1 import roslib; roslib.load_manifest('simple_arm_server')
2 import rospy
3 import sys
4
5 import tf
6 from tf.transformations import euler_from_quaternion, quaternion_from_euler
7
8 from simple_arm_server.msg import *
9 from simple_arm_server.srv import *
10
11 if __name__ == '__main__':
12 rospy.init_node('simple_arm_server_test')
13 rospy.wait_for_service('simple_arm_server/move')
14 move_srv = rospy.ServiceProxy('simple_arm_server/move', MoveArm)
15
16 req = MoveArmRequest()
17 req.header.frame_id = "base_link"
18
19 action = ArmAction()
20 action.type = ArmAction.MOVE_ARM
21 action.goal.position.x = 0.2
22 action.goal.position.y = -0.09
23 action.goal.position.z = .1
24 q = quaternion_from_euler(0.0, 1.57, 0.0, 'sxyz')
25 action.goal.orientation.x = q[0]
26 action.goal.orientation.y = q[1]
27 action.goal.orientation.z = q[2]
28 action.goal.orientation.w = q[3]
29 action.move_time = rospy.Duration(5.0)
30 req.goals.append(action)
31
32 action = ArmAction()
33 action.type = ArmAction.MOVE_GRIPPER
34 action.command = 0.03
35 action.move_time = rospy.Duration(1.0)
36 req.goals.append(action)
37
38 action = ArmAction()
39 action.type = ArmAction.MOVE_ARM
40 action.goal.position.x = 0.2
41 action.goal.position.y = -0.09
42 action.goal.position.z = .04
43 q = quaternion_from_euler(0.0, 1.57, 0.0, 'sxyz')
44 action.goal.orientation.x = q[0]
45 action.goal.orientation.y = q[1]
46 action.goal.orientation.z = q[2]
47 action.goal.orientation.w = q[3]
48 action.move_time = rospy.Duration(1.0)
49 req.goals.append(action)
50
51 action = ArmAction()
52 action.type = ArmAction.MOVE_GRIPPER
53 action.command = 0.0254
54 action.move_time = rospy.Duration(2.0)
55 req.goals.append(action)
56
57 action = ArmAction()
58 action.type = ArmAction.MOVE_ARM
59 action.goal.position.x = 0.2
60 action.goal.position.y = -0.09
61 action.goal.position.z = .1
62 q = quaternion_from_euler(0.0, 1.57, 0.0, 'sxyz')
63 action.goal.orientation.x = q[0]
64 action.goal.orientation.y = q[1]
65 action.goal.orientation.z = q[2]
66 action.goal.orientation.w = q[3]
67 action.move_time = rospy.Duration(1.0)
68 req.goals.append(action)
69
70 action = ArmAction()
71 action.type = ArmAction.MOVE_ARM
72 action.goal.position.x = 0.2
73 action.goal.position.y = 0.09
74 action.goal.position.z = .1
75 q = quaternion_from_euler(0.0, 1.57, 0.0, 'sxyz')
76 action.goal.orientation.x = q[0]
77 action.goal.orientation.y = q[1]
78 action.goal.orientation.z = q[2]
79 action.goal.orientation.w = q[3]
80 action.move_time = rospy.Duration(5.0)
81 req.goals.append(action)
82
83 action = ArmAction()
84 action.type = ArmAction.MOVE_GRIPPER
85 action.command = 0.03
86 action.move_time = rospy.Duration(2.0)
87 req.goals.append(action)
88
89 action = ArmAction()
90 action.type = ArmAction.MOVE_GRIPPER
91 action.command = 0.0254
92 action.move_time = rospy.Duration(1.0)
93 req.goals.append(action)
94
95 try:
96 r = move_srv(req)
97 print r
98 except rospy.ServiceException, e:
99 print "Service did not process request: %s"%str(e)
Summary
This tutorial has shown how to move the arm through a series of poses. This can be used for simple pick and place, although the server offers no collision checking. Please see the Moving the Arm tutorial for Mini Maxwell for a specific example.