The example demonstrates basic joint position control. A joint position waypoint is a configuration of the arm in joint space (ie. simultaneous joint angles for the arm's seven degrees of freedom). In this example, we enable the robot moving the limb in zero-g mode. Interacting with the arm's navigator buttons, we can record a sequence of joint position waypoints. Upon completion of recording, we will continuously command the limb loop through the recorded joint sequence.
Introduction
This example demonstrates the usage of the position controller for simple joint position moves. The main() function calls the record() method which records the waypoints as desired by the user. Then, the playback() method is invoked which demonstrates a smooth motion playback through the recorded joint positions.
Interfaces -
- Limb.move_to_joint_positions()
- Limb.set_joint_position_speed()
- Limb.joint_angles()
- Navigator.wheel()
- Navigator.button_state()
If you would like to follow along with the actual source code for the example on GitHub, it can be found through this link for joint position waypoints example.
Usage
Verify that the robot is enabled from an SDK terminal session, ex:
$ rosrun intera_interface robot_enable.py
Start the joint position waypoints example program, you can specify the joint position motion speed ratio -s or joint position accuracy(rad) -a on which we will run the example.
For example, run the example with 0.1 speed ratio and 0.1 accuracy:
$ rosrun intera_examples joint_position_waypoints.py -s 0.1 -a 0.1
Moving the arm in zero-g mode, when we reach a joint position configuration we would like to record, press that navigator wheel.
You will then be prompted with instructions for recording joint position waypoints.
Press Navigator 'OK/Wheel' button to record a new joint joint position waypoint.
Press Navigator 'Rethink' button when finished recording waypoints to begin playback.
Moving the arm in zero-g mode, when we reach a joint position configuration we would like to record, press that navigator wheel.
You will get the feedback that the joint position waypoint has been recorded:
Waypoint Recorded
When done recording waypoints, pressing the navigator's 'Rethink' button will begin playback.
[INFO] [WallTime: 1399571721.540300] Waypoint Playback Started
Press Ctrl-C to stop...
The program will begin looping through the recorded joint positions. When the previous joint position command is fully achieved (within the accuracy threshold), the next recorded joint position will be commanded.
Waypoint playback loop #1
Waypoint playback loop #2
...
Pressing Control-C at any time will stop playback and exit the example.
Arguments
Important Arguments:
-s or --speed : The joint position motion speed ratio [0.0-1.0] (default:= 0.3)
-a or --accuracy : The threshold in Radians at which the current joint position command is considered successful before sending the next following joint position command. (default:= 0.008726646)
See the joint position waypoint's available arguments on the command line by passing joint_position_waypoints.py the -h, help argument:
$ rosrun intera_examples joint_position_waypoints.py -h
usage: joint_position_waypoints.py [-h] [-s SPEED] [-a ACCURACY]
RSDK Joint Position Waypoints Example
Records joint positions each time the navigator 'OK/wheel'
button is pressed.
Upon pressing the navigator 'Rethink' button, the recorded joint positions
will begin playing back in a loop.
optional arguments:
-h, --help show this help message and exit
-s SPEED, --speed SPEED
joint position motion speed ratio [0.0-1.0] (default:=
0.3)
-a ACCURACY, --accuracy ACCURACY
joint position accuracy (rad) at which waypoints must
achieve
Code Walkthrough
Now, let's break down the code.
33 import argparse
34 import sys
35
36 import rospy
37
38 import intera_interface
This imports the intera interface for accessing the limb and the gripper class.
41 class Waypoints(object):
42 def __init__(self, speed, accuracy, limb="right"):
43 # Create intera_interface limb instance
44 self._arm = limb
45 self._limb = intera_interface.Limb(self._arm)
46
47 # Parameters which will describe joint position moves
48 self._speed = speed
49 self._accuracy = accuracy
50
51 # Recorded waypoints
52 self._waypoints = list()
53
54 # Recording state
55 self._is_recording = False
56
57 # Verify robot is enabled
58 print("Getting robot state... ")
59 self._rs = intera_interface.RobotEnable()
60 self._init_state = self._rs.state().enabled
61 print("Enabling robot... ")
62 self._rs.enable()
63
64 # Create Navigator I/O
65 self._navigator_io = intera_interface.Navigator(self._arm)
An instance of the limb interface for the side under interest is created. An instance of the interface for the corresponding navigator, _navigator_io, is also created. The robot is then enabled. It is important to note that the robot should be enabled in order to control the limb's movement.
67 def _record_waypoint(self, value):
68 """
69 Stores joint position waypoints
70
71 Navigator 'OK/Wheel' button callback
72 """
73 if value != 'OFF':
74 print("Waypoint Recorded")
75 self._waypoints.append(self._limb.joint_angles())
The joint_angles() method retrieves the current joint angles and they are then appended to the _waypoints list.
77 def _stop_recording(self, value):
78 """
79 Sets is_recording to false
80
81 Navigator 'Rethink' button callback
82 """
83 # On navigator Rethink button press, stop recording
84 if value != 'OFF':
85 print("Recording Stopped")
86 self._is_recording = False
This Rethink button's press event is captured.
88 def record(self):
89 """
90 Records joint position waypoints upon each Navigator 'OK/Wheel' button
91 press.
92 """
93 rospy.loginfo("Waypoint Recording Started")
94 print("Press Navigator 'OK/Wheel' button to record a new joint "
95 "joint position waypoint.")
96 print("Press Navigator 'Rethink' button when finished recording "
97 "waypoints to begin playback")
98 # Connect Navigator callbacks
99 # Navigator scroll wheel button press
100 ok_id = self._navigator.register_callback(self._record_waypoint, 'right_button_ok')
101 # Navigator Rethink button press
102 show_id = self._navigator.register_callback(self._stop_recording, 'right_button_show')
103
104 # Set recording flag
105 self._is_recording = True
106
107 # Loop until waypoints are done being recorded ('Rethink' Button Press)
108 while not rospy.is_shutdown() and self._is_recording:
109 rospy.sleep(1.0)
110
111 # We are now done with the navigator callbacks, disconnecting them
112 self._navigator.deregister_callback(ok_id)
113 self._navigator.deregister_callback(show_id)
The navigator 'OK/Wheel' button invokes the _record_waypoint() method on a press event, which records the current joint positions as explained above. Similarly, the navigator 'Rethink' button invokes the _stop_recording method on a press event, which sets the is_recording variable to false.
115 def playback(self):
116 """
117 Loops playback of recorded joint position waypoints until program is
118 exited
119 """
120 rospy.sleep(1.0)
121
122 rospy.loginfo("Waypoint Playback Started")
123 print(" Press Ctrl-C to stop...")
124
125 # Set joint position speed ratio for execution
126 self._limb.set_joint_position_speed(self._speed)
127
128 # Loop until program is exited
129 loop = 0
130 while not rospy.is_shutdown():
131 loop += 1
132 print("Waypoint playback loop #%d " % (loop,))
133 for waypoint in self._waypoints:
134 if rospy.is_shutdown():
135 break
136 self._limb.move_to_joint_positions(waypoint, timeout=20.0,
137 threshold=self._accuracy)
138 # Sleep for a few seconds between playback loops
139 rospy.sleep(3.0)
140
141 # Set joint position speed back to default
142 self._limb.set_joint_position_speed(0.3)
The set_joint_position_speed() method sets the ratio of max joint speed to use during joint position moves. The method move_to_joint_positions(), moves the joints to the commanded position. It is important to note that there is not trajectory planning involved here. Instead, this is passed onto a low pass filter and the intermediate positions between the start and goal positions are obtained. They are then published as a joint command message using the set_joint_positions() method. Thus, all the waypoints that were stored are visited along a smooth trajectory.
144 def clean_shutdown(self):
145 print("\nExiting example...")
146 if not self._init_state:
147 print("Disabling robot...")
148 self._rs.disable()
149 return True
On shutdown, the robot is sent to its initial state that was captured.
152 def main():
153 """RSDK Joint Position Waypoints Example
154
155 Records joint positions each time the navigator 'OK/wheel'
156 button is pressed.
157 Upon pressing the navigator 'Rethink' button, the recorded joint positions
158 will begin playing back in a loop.
159 """
160 arg_fmt = argparse.RawDescriptionHelpFormatter
161 parser = argparse.ArgumentParser(formatter_class=arg_fmt,
162 description=main.__doc__)
163 parser.add_argument(
164 '-s', '--speed', default=0.3, type=float,
165 help='joint position motion speed ratio [0.0-1.0] (default:= 0.3)'
166 )
167 parser.add_argument(
168 '-a', '--accuracy',
169 default=intera_interface.settings.JOINT_ANGLE_TOLERANCE, type=float,
170 help='joint position accuracy (rad) at which waypoints must achieve'
171 )
172 args = parser.parse_args(rospy.myargv()[1:])
The speed and accuracy on which the example is to be demonstrated is captured from the command line arguments.
178 print("Initializing node... ")
179 rospy.init_node("rsdk_joint_position_waypoints")
180
181 waypoints = Waypoints(args.speed, args.accuracy)
182
183 # Register clean shutdown
184 rospy.on_shutdown(waypoints.clean_shutdown)
185
186 # Begin example program
187 waypoints.record()
188 waypoints.playback()
189
190 if __name__ == '__main__':
191 main()
The node is initialized and an instance of the Waypoints class is created. The user defined waypoints are recorded using the record() method and are played back using the playback() method as explained above.
