Joint Position Example

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The joint position example(keyboard, joystick) demonstrates basic joint position control. The key or button mapped to either increasing or decreasing the angle of a particular joint on Sawyer's arm.

Usage

Start the joint position keyboard example program, ex:

$ rosrun intera_examples joint_position_keyboard.py

Start the joint position joystick example program, ex:

$ rosrun intera_examples joint_position_joystick.py

Upon startup, you will be prompted with the following:

Initializing node... 
Getting robot state... 
Enabling robot... 
[INFO] [WallTime: 1399575163.891211] Robot Enabled
Controlling joints. Press ? for help, Esc to quit.

Arguments

Important Arguments:

See the joint position example available arguments on the command line by passing:

$ rosrun intera_examples joint_position_keyboard.py -h
usage: joint_position_keyboard.py [-h] [-l LIMB]

RSDK Joint Position Example: Keyboard Control
    Use your dev machine's keyboard to control joint positions.
    Each key corresponds to increasing or decreasing the angle
    of a joint on Sawyer's arm. The increasing and descreasing
    are represented by number key and letter key next to the number.
    

optional arguments:
  -h, --help            show this help message and exit
  -l LIMB, --limb LIMB
                        Limb on which to run the joint position keyboard example

For joint position joystick example:

$ rosrun intera_examples joint_position_joystick.py -h
usage: joint_position_joystick.py [-h] [-l LIMB] [-j JOYSTICK]

SDK Joint Position Example: Joystick Control
    Use a game controller to control the angular joint positions
    of Sawyer's arms.
    Attach a game controller to your dev machine and run this
    example along with the ROS joy_node to control the position
    of each joint in Sawyer's arm using the joystick. Be sure to
    provide your *joystick* type to setup appropriate key mappings.
    Each stick axis maps to a joint angle; which joints are currently
    controlled can be incremented by using the mapped increment buttons.
    Ex:
      (x,y -> e0,e1) >>increment>> (x,y -> e1,e2)

required arguments:
  -j, --joystick        specify the type of joystick to use

optional arguments:
  -h, --help            show this help message and exit
  -l LIMB, --limb LIMB
                        Limb on which to run the joint position joystick example


Joint Position Keyboard Code Walkthrough

Now, let's break down the code.

33 """
34 SDK Joint Position Example: keyboard
35 """
36 import argparse
37 
38 import rospy
39 
40 import intera_interface
41 import intera_external_devices
42 
43 from intera_interface import CHECK_VERSION

This imports the intera interface for accessing the limb and the gripper class. The intera_external_devices is imported to use its getch function, that captures the key presses on the keyboard. The CHECK_VERSION is imported to check if the software running on the robot would be compatible with this local version. It is not necessary to check the version in custom programs.

43 def map_keyboard(side):
44     limb = intera_interface.Limb(side)
45     
46     try:
47         gripper = intera_interface.Gripper(side)
48     except:
49         has_gripper = False
50         rospy.logerr("Could not initalize the gripper.")
51     else:
52         has_gripper = True
53 
54     joints = limb.joint_names()

The instance of Limb class, limb and the instance of Gripper class, gripper are created. joint_names() method returns an array of joints of the limb.

56     def set_j(limb, joint_name, delta):
57         current_position = limb.joint_angle(joint_name)
58         joint_command = {joint_name: current_position + delta}
59         limb.set_joint_positions(joint_command)
60 
61     def set_g(action):
62         if has_gripper:
63             if action == "close":
64                 gripper.close()
65             elif action == "open":
66                 gripper.open()
67             elif action == "calibrate":
68                 gripper.calibrate()

The set_j() function is invoked whenever a valid key press occurs. The limb refers to the limb instance of Sawyer's limb. delta refers to the required displacement of the joint from its current position. The method joint_angle() returns the current position of that joint. Then the joint command message is updated for that corresponding joint to indicate the new position. set_joint_position() method publishes the joint commands to the position controller. The set_g function calls gripper action function(open(), or close() or calibrate()) when corresponding action is provided.

70     bindings = {
71         '1': (set_j, [limb, joints[0], 0.1], joints[0]+" increase"),
72         'q': (set_j, [limb, joints[0], -0.1], joints[0]+" decrease"),
73         '2': (set_j, [limb, joints[1], 0.1], joints[1]+" increase"),
74         'w': (set_j, [limb, joints[1], -0.1], joints[1]+" decrease"),
75         '3': (set_j, [limb, joints[2], 0.1], joints[2]+" increase"),
76         'e': (set_j, [limb, joints[2], -0.1], joints[2]+" decrease"),
77         '4': (set_j, [limb, joints[3], 0.1], joints[3]+" increase"),
78         'r': (set_j, [limb, joints[3], -0.1], joints[3]+" decrease"),
79         '5': (set_j, [limb, joints[4], 0.1], joints[4]+" increase"),
80         't': (set_j, [limb, joints[4], -0.1], joints[4]+" decrease"),
81         '6': (set_j, [limb, joints[5], 0.1], joints[5]+" increase"),
82         'y': (set_j, [limb, joints[5], -0.1], joints[5]+" decrease"),
83         '7': (set_j, [limb, joints[6], 0.1], joints[6]+" increase"),
84         'u': (set_j, [limb, joints[6], -0.1], joints[6]+" decrease"),
85         '8': (set_g, "close", side+" gripper close"),
86         'i': (set_g, "open", side+" gripper open"),
87         '9': (set_g, "calibrate", side+" gripper calibrate")
88      }

The bindings is a dictionary that holds the set of characters in the keyboard and their corresponding joints.

89     done = False
90     print("Controlling joints. Press ? for help, Esc to quit.")
91     while not done and not rospy.is_shutdown():
92         c = intera_external_devices.getch()
93         if c:
94             #catch Esc or ctrl-c
95             if c in ['\x1b', '\x03']:
96                 done = True
97                 rospy.signal_shutdown("Example finished.")

The done variable captures whether "esc" or "ctrl-c" was hit. The while loop iterates as long as the "esc" or "ctrl-c" is hit or ros-shutdown signal is given. c captures the keyboard input. If "esc" or "ctrl-c" is given then done gets updated as true, and a shutdown signal will be sent.

 98             elif c in bindings:
 99                 cmd = bindings[c]
100                 if c == '8' or c == 'i' or c == '9':
101                     cmd[0](cmd[1])
102                     print("command: %s" % (cmd[2],))
103                 else:
104                     #expand binding to something like "set_j(right, 'j0', 0.1)"
105                     cmd[0](*cmd[1])
106                     print("command: %s" % (cmd[2],))

The user inputted key is checked whether it is in the bindings dictionary. bindings[c] returns the value of the key c from the dictionary. The 0th index of the value refers to the function to be called and the next index holds the arguments to be sent along with that function. cmd[2] is the description of the joint command from the dictionary above.

107             else:
108                 print("key bindings: ")
109                 print("  Esc: Quit")
110                 print("  ?: Help")
111                 for key, val in sorted(bindings.items(),
112                                        key=lambda x: x[1][2]):
113                     print("  %s: %s" % (key, val[2]))

This case is executed when the key pressed is not a valid input. So, the key is sorted and is printed along with its corresponding description.

115 def main():
116     """RSDK Joint Position Example: Keyboard Control
117     Use your dev machine's keyboard to control joint positions.
118     Each key corresponds to increasing or decreasing the angle
119     of a joint on Sawyer's arm. The increasing and descreasing
120     are represented by number key and letter key next to the number.
121     """
122     epilog = """
123 See help inside the example with the '?' key for key bindings.
124     """
125     rp = intera_interface.RobotParams()
126     valid_limbs = rp.get_limb_names()
127     if not valid_limbs:
128         rp.log_message(("Cannot detect any limb parameters on this robot. "
129                         "Exiting."), "ERROR")
130         return
131     arg_fmt = argparse.RawDescriptionHelpFormatter
132     parser = argparse.ArgumentParser(formatter_class=arg_fmt,
133                                      description=main.__doc__,
134                                      epilog=epilog)
135     parser.add_argument(
136         "-l", "--limb", dest="limb", default=valid_limbs[0],
137         choices=valid_limbs,
138         help="Limb on which to run the joint position keyboard example"
139     )
140     args = parser.parse_args(rospy.myargv()[1:])
141 
142     print("Initializing node... ")
143     rospy.init_node("sdk_joint_position_keyboard")
144     print("Getting robot state... ")
145     rs = intera_interface.RobotEnable(CHECK_VERSION)
146     init_state = rs.state().enabled

The node is initialized and then the software version is checked for compatiblity with the local version. init_state captures Sawyer's initial state. This is to make sure that Sawyer is sent back to the same state after the program exits.

150     def clean_shutdown():
151         print("\nExiting example.")
152         if not init_state:
153             print("Disabling robot...")
154             rs.disable()
155     rospy.on_shutdown(clean_shutdown)

As explained above, the robot is checked if it was initially disabled and if so, it is disabled upon the program's termination.

157     rospy.loginfo("Enabling robot...")
158     rs.enable()
159     map_keyboard(args.limb)
160     print("Done.")
161 
162 
163 if __name__ == '__main__':
164     main()

The robot is enabled before the programs execution. It is important to note that Sawyer should be auto-enabled before trying to move its joints. map_keyboard() function captures the key input and moves the joint as explained above.

Joint Position Joystick Code Walkthrough

Now, let's break down the code.

33 import argparse
34 
35 import rospy
36 
37 import intera_interface
38 import intera_external_devices
39 
40 from intera_interface import CHECK_VERSION

This imports the intera interface for accessing the limb and the gripper class. The intera_external_devices is imported to use its joystick function, that captures the key presses on the joystick. The CHECK_VERSION is imported to check if the software running on the robot would be compatible with this local version. It is not necessary to check the version in custom programs.

43 def rotate(l):
44     """
45     Rotates a list left.
46     @param l: the list
47     """
48     if len(l):
49         v = l[0]
50         l[:-1] = l[1:]
51         l[-1] = v

The rotate function rotates a list, it will be used in bindings. This moves all the elements in the list to one position to their left. So the element at 0th position moves to the nth position, element at nth position moves to (n-1)th position, and so on.

54 def set_j(cmd, limb, joints, index, delta):
55     """
56     Set the selected joint to current pos + delta.
57     @param cmd: the joint command dictionary
58     @param limb: the limb to get the pos from
59     @param joints: a list of joint names
60     @param index: the index in the list of names
61     @param delta: delta to update the joint by
62     joint/index is to make this work in the bindings.
63     """
64     joint = joints[index]
65     cmd[joint] = delta + limb.joint_angle(joint)

joint_angle() method returns the current angle of the corresponding joint. This function builds the dictionary that is to be passed as a joint command. The last line assigns the new position which has an offset of delta from the current position.

69 def map_joystick(joystick, side):
70     """
71     Maps joystick input to joint position commands.
72     @param joystick: an instance of a Joystick
73     """
74     limb = intera_interface.Limb(side)
75     gripper = None
76     try:
77         gripper = intera_interface.Gripper(side)
78     except:
79         rospy.loginfo("Could not detect a connected electric gripper.")

The instance of Limb class and the instance of Gripper class are created. No gripper will raise could not detect gripper info.

82     def set_g(action):
83         if gripper is not None:
84             if action == "close":
85                 gripper.close()
86             elif action == "open":
87                 gripper.open()
88             elif action == "calibrate":
89                 gripper.calibrate()

The set_g function calls gripper action function(open(), or close() or calibrate()) when corresponding action is provided.

 91     limb_cmd = {}
 92 
 93     #available joints
 94     joints = limb.joint_names()
 95 
 96     #abbreviations
 97     jhi = lambda s: joystick.stick_value(s) > 0
 98     jlo = lambda s: joystick.stick_value(s) < 0
 99     bdn = joystick.button_down
100     bup = joystick.button_up

Create instance of joint names and abbreviations for joystick values, button up and button down. The joint_names() method returns a list of joints associated with the limb. The stick_value() method returns the dead-banded, scaled and offset value of the axis. The abbreviations for all these functions are created to be used within the bindings dictionary below.

102     def print_help(bindings_list):
103         print("Press Ctrl-C to quit.")
104         for bindings in bindings_list:
105             for (test, _cmd, doc) in bindings:
106                 if callable(doc):
107                     doc = doc()
108                 print("%s: %s" % (str(test[1][0]), doc))

The information about the joystick buttons and the corresponding joints are displayed. This information is available in bindings_list as below. The doc refers to the last element of the tuple and it is checked if it is a callable function. So, if there is a lambda function that evaluates and returns a string, then that function is called. Finally, the results are displayed.

110     bindings_list = []
111     bindings = [
112         ((jlo, ['leftStickHorz']), (set_j, [limb_cmd, limb, joints, 0, 0.1]),
113             lambda: "Increase " + joints[0]),
114         ((jhi, ['leftStickHorz']), (set_j, [limb_cmd, limb, joints, 0, -0.1]),
115             lambda: "Decrease " + joints[0]),
116         ((jlo, ['leftStickVert']), (set_j, [limb_cmd, limb, joints, 1, 0.1]),
117             lambda: "Increase " + joints[1]),
118         ((jhi, ['leftStickVert']), (set_j, [limb_cmd, limb, joints, 1, -0.1]),
119             lambda: "Decrease " + joints[1]),
120         ((jlo, ['rightStickHorz']), (set_j, [limb_cmd, limb, joints, 2, 0.1]),
121             lambda: "Increase " + joints[2]),
122         ((jhi, ['rightStickHorz']), (set_j, [limb_cmd, limb, joints, 2, -0.1]),
123             lambda: "Decrease " + joints[2]),
124         ((jlo, ['rightStickVert']), (set_j, [limb_cmd, limb, joints, 3, 0.1]),
125             lambda: "Increase " + joints[3]),
126         ((jhi, ['rightStickVert']), (set_j, [limb_cmd, limb, joints, 3, -0.1]),
127             lambda: "Decrease " + joints[3]),
128         ((bdn, ['leftBumper']), (rotate, [joints]), side + ": cycle joint"),
129         ((bdn, ['function1']), (print_help, [bindings_list]), "help"),
130         ((bdn, ['function2']), (print_help, [bindings_list]), "help"),
131         ]
132     if gripper:
133         bindings.extend([
134             ((bdn, ['rightTrigger']), (set_g, ['close'], gripper), side + " gripper close"),
135             ((bup, ['rightTrigger']), (set_g, ['open'], gripper), side + " gripper open"),
136             ((bdn, ['btnLeft']), (set_g, ['calibrate'], gripper), "right calibrate")
137             ])
138     bindings_list.append(bindings)

The first element of every tuple refers to the command that has to be executed. As indicated above set_j, bdn, bup, jhi and jlo refers to the function and their acronyms. The second tuple has a list that holds the list of arguments to be passed along with that function. The last element holds a string or a function that evaluates and forms a string to detail the joint under consideration.

140     rate = rospy.Rate(100)
141     print_help(bindings_list)
142     print("Press Ctrl-C to stop. ")
143     while not rospy.is_shutdown():
144         for (test, cmd, doc) in bindings:
145             if test[0](*test[1]):
146                 cmd[0](*cmd[1])
147                 if callable(doc):
148                     print(doc())
149                 else:
150                     print(doc)
151         if len(limb_cmd):
152             limb.set_joint_positions(limb_cmd)
153             limb_cmd.clear()
154         rate.sleep()
155     return False

The test tuple holds the function that needs to be called for a particular value to be tested. For instance, the first tuple holds the abbreviation bdn and the parameter rightTrigger that is passed along. This test function checks whether the joystick's button_down is pressed. If this is true then the cmd, that refers to the second tuple (gripper.close,[]) is parsed as above. For the first binding, the expression cmd[0](*cmd[1]) returns the function call gripper.close([]). The next line checks if the last tuple is a function (lambda) or not (string). Since the joints being controlled are updated dynamically, the lambda function is used to retrieve the current joints rj[0] and rj[1]. The dictionaries limb_cmd hold the joint commands for the limb. These dictionaries get populated when the set_j method is called by the previous section of code.

158 def main():
159     """SDK Joint Position Example: Joystick Control
160     Use a game controller to control the angular joint positions
161     of Sawyer's arms.
162     Attach a game controller to your dev machine and run this
163     example along with the ROS joy_node to control the position
164     of each joint in Sawyer's arm using the joystick. Be sure to
165     provide your *joystick* type to setup appropriate key mappings.
166     Each stick axis maps to a joint angle; which joints are currently
167     controlled can be incremented by using the mapped increment buttons.
168     Ex:
169       (x,y -> e0,e1) >>increment>> (x,y -> e1,e2)
170     """
171     epilog = """
172 See help inside the example with the "Start" button for controller
173 key bindings.
174     """
175     rp = intera_interface.RobotParams()
176     valid_limbs = rp.get_limb_names()
177     if not valid_limbs:
178         rp.log_message(("Cannot detect any limb parameters on this robot. "
179                         "Exiting."), "ERROR")
180         return
181     arg_fmt = argparse.RawDescriptionHelpFormatter
182     parser = argparse.ArgumentParser(formatter_class=arg_fmt,
183                                      description=main.__doc__,
184                                      epilog=epilog)
185     required = parser.add_argument_group('required arguments')
186     required.add_argument(
187         '-j', '--joystick', required=True,
188         choices=['xbox', 'logitech', 'ps3'],
189         help='specify the type of joystick to use'
190     )
191     parser.add_argument(
192         "-l", "--limb", dest="limb", default=valid_limbs[0],
193         choices=valid_limbs,
194         help="Limb on which to run the joint position joystick example"
195     )
196     args = parser.parse_args(rospy.myargv()[1:])
197 
198     joystick = None
199     if args.joystick == 'xbox':
200         joystick = intera_external_devices.joystick.XboxController()
201     elif args.joystick == 'logitech':
202         joystick = intera_external_devices.joystick.LogitechController()
203     elif args.joystick == 'ps3':
204         joystick = intera_external_devices.joystick.PS3Controller()
205     else:
206         parser.error("Unsupported joystick type '%s'" % (args.joystick))
207 
208     print("Initializing node... ")
209     rospy.init_node("sdk_joint_position_joystick")
210     print("Getting robot state... ")
211     rs = intera_interface.RobotEnable(CHECK_VERSION)
212     init_state = rs.state().enabled

The type of joystick input is captured as entered by the user and an instance of the corresponding interface is created. The node is initialized and the robot is enabled.

217     def clean_shutdown():
218         print("\nExiting example.")
219         if not init_state:
220             print("Disabling robot...")
221             rs.disable()
222     rospy.on_shutdown(clean_shutdown)
223 
224     rospy.loginfo("Enabling robot...")
225     rs.enable()
226 
227     map_joystick(joystick, args.limb)
228     print("Done.")
229 
230 
231 if __name__ == '__main__':
232     main()

The map_joystick() method performs the mapping and execution of the commands as explained above.