Introduction
This example demonstrates the usage of the gripper control via baxter interface. The main() function enables the robot and invokes the map_keyboard() function. It is at this function where the keyboard keys are mapped to individual gripper actions and the commands are executed periodically.
Interfaces -
- Gripper.reboot()
- Gripper.calibrate()
- Gripper.close()
- Gripper.open()
- Gripper.set_velocity(<double>)
- Gripper.stop()
- Gripper.position()
- Gripper.command_position(<double>,<double>)
- Gripper.parameters()
- Gripper.set_holding_force(<double>, <double>)
- Gripper.set_moving_force(<double>, <double>)
- Gripper.set_velocity(<double>, <double>)
- Gripper.set_dead_band(<double>, <double>)
Code Walkthrough
Now, let's break down the code.
33 import argparse
34
35 import rospy
36
37 import baxter_interface
38 import baxter_external_devices
39
40 from baxter_interface import CHECK_VERSION
This imports the baxter interface for accessing the limb and the gripper class. The baxter_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():
44 # initialize interfaces
45 print("Getting robot state... ")
46 rs = baxter_interface.RobotEnable(CHECK_VERSION)
47 init_state = rs.state().enabled
48 left = baxter_interface.Gripper('left', CHECK_VERSION)
49 right = baxter_interface.Gripper('right', CHECK_VERSION)
The init_state variable captures the current state of the robot. Two instances of the Gripper class are created for either of Baxter's limbs.
51 def clean_shutdown():
52 if not init_state:
53 print("Disabling robot...")
54 rs.disable()
55 print("Exiting example.")
56 rospy.on_shutdown(clean_shutdown)
On shutdown request, Baxter's state is sent back to its initial state.
58 def capability_warning(gripper, cmd):
59 msg = ("%s %s - not capable of '%s' command" %
60 (gripper.name, gripper.type(), cmd))
61 rospy.logwarn(msg)
This function is invoked when a gripper control command is called with custom grippers. It displays a warning message.
63 def offset_position(gripper, offset):
64 if gripper.type() != 'electric':
65 capability_warning(gripper, 'command_position')
66 return
67 current = gripper.position()
68 gripper.command_position(current + offset)
The gripper type is checked for an electric gripper. command_position() sets the gripper to the commanded position. It moves the fingers from close(0) to open(100) state based on the passed double value.
70 def offset_holding(gripper, offset):
71 if gripper.type() != 'electric':
72 capability_warning(gripper, 'set_holding_force')
73 return
74 current = gripper.parameters()['holding_force']
75 gripper.set_holding_force(current + offset)
set_holding_force() method is used to set the force of the grippers when the fingers come in contact with an object between them.
77 def offset_moving(gripper, offset):
78 if gripper.type() != 'electric':
79 capability_warning(gripper, 'set_moving_force')
80 return
81 current = gripper.parameters()['moving_force']
82 gripper.set_moving_force(current + offset)
set_moving_force() method is used to set the force of the grippers immediately before the fingers come in contact with an object between them.
84 def offset_velocity(gripper, offset):
85 if gripper.type() != 'electric':
86 capability_warning(gripper, 'set_velocity')
87 return
88 current = gripper.parameters()['velocity']
89 gripper.set_velocity(current + offset)
set_velocity() method is used to set the velocity at which the grippers would open/close.
91 def offset_dead_band(gripper, offset):
92 if gripper.type() != 'electric':
93 capability_warning(gripper, 'set_dead_band')
94 return
95 current = gripper.parameters()['dead_zone']
96 gripper.set_dead_band(current + offset)
set_dead_band() method is used to set the dead zone of the grippers. Precisely, it refers to the minimum distance between the gripper fingers when they are in closed state.
98 bindings = {
99 # key: (function, args, description)
100 'r': (left.reboot, [], "left: reboot"),
101 'R': (right.reboot, [], "right: reboot"),
102 'c': (left.calibrate, [], "left: calibrate"),
103 'C': (right.calibrate, [], "right: calibrate"),
104 'q': (left.close, [], "left: close"),
105 'Q': (right.close, [], "right: close"),
106 'w': (left.open, [], "left: open"),
107 'W': (right.open, [], "right: open"),
108 '[': (left.set_velocity, [100.0], "left: set 100% velocity"),
109 '{': (right.set_velocity, [100.0], "right: set 100% velocity"),
110 ']': (left.set_velocity, [30.0], "left: set 30% velocity"),
111 '}': (right.set_velocity, [30.0], "right: set 30% velocity"),
112 's': (left.stop, [], "left: stop"),
113 'S': (right.stop, [], "right: stop"),
114 'z': (offset_dead_band, [left, -1.0], "left: decrease dead band"),
115 'Z': (offset_dead_band, [right, -1.0], "right: decrease dead band"),
116 'x': (offset_dead_band, [left, 1.0], "left: increase dead band"),
117 'X': (offset_dead_band, [right, 1.0], "right: increase dead band"),
118 'f': (offset_moving, [left, -5.0], "left: decrease moving force"),
119 'F': (offset_moving, [right, -5.0], "right: decrease moving force"),
120 'g': (offset_moving, [left, 5.0], "left: increase moving force"),
121 'G': (offset_moving, [right, 5.0], "right: increase moving force"),
122 'h': (offset_holding, [left, -5.0], "left: decrease holding force"),
123 'H': (offset_holding, [right, -5.0], "right: decrease holding force"),
124 'j': (offset_holding, [left, 5.0], "left: increase holding force"),
125 'J': (offset_holding, [right, 5.0], "right: increase holding force"),
126 'v': (offset_velocity, [left, -5.0], "left: decrease velocity"),
127 'V': (offset_velocity, [right, -5.0], "right: decrease velocity"),
128 'b': (offset_velocity, [left, 5.0], "left: increase velocity"),
129 'B': (offset_velocity, [right, 5.0], "right: increase velocity"),
130 'u': (offset_position, [left, -15.0], "left: decrease position"),
131 'U': (offset_position, [right, -15.0], "right: decrease position"),
132 'i': (offset_position, [left, 15.0], "left: increase position"),
133 'I': (offset_position, [right, 15.0], "right: increase position"),
134 }
The bindings is a dictionary that holds the set of characters in the keyboard and their corresponding gripperfunctions.
136 done = False
137 print("Enabling robot... ")
138 rs.enable()
139 print("Controlling grippers. Press ? for help, Esc to quit.")
140 while not done and not rospy.is_shutdown():
141 c = baxter_external_devices.getch()
142 if c:
143 if c in ['\x1b', '\x03']:
144 done = True
The done variable is used to capture if "esc" or "ctrl-c" was hit. The while loop iterates till the "esc" or "ctrl-c" is inputted 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 shutdown signal is sent.
145 elif c in bindings:
146 cmd = bindings[c]
147 cmd[0](*cmd[1])
148 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.
149 else:
150 print("key bindings: ")
151 print(" Esc: Quit")
152 print(" ?: Help")
153 for key, val in sorted(bindings.items(),
154 key=lambda x: x[1][2]):
155 print(" %s: %s" % (key, val[2]))
156 # force shutdown call if caught by key handler
157 rospy.signal_shutdown("Example finished.")
This case is executed when the key pressed is not valid. So, the key is sorted and printed along with its corresponding description.
160 def main():
161 """RSDK Gripper Example: Keyboard Control
162
163 Use your dev machine's keyboard to control and configure
164 Baxter's grippers.
165
166 Run this example to command various gripper movements while
167 adjusting gripper parameters, including calibration, velocity,
168 and force. Uses the baxter_interface.Gripper class and the
169 helper function, baxter_external_devices.getch.
170 """
171 epilog = """
172 See help inside the example with the '?' key for key bindings.
173 """
174 arg_fmt = argparse.RawDescriptionHelpFormatter
175 parser = argparse.ArgumentParser(formatter_class=arg_fmt,
176 description=main.__doc__,
177 epilog=epilog)
178 parser.parse_args(rospy.myargv()[1:])
179
180 print("Initializing node... ")
181 rospy.init_node("rsdk_gripper_keyboard")
The node is initialized.
183 map_keyboard()
184
185
186 if __name__ == '__main__':
187 main()
It is important to note that Baxter should be enabled before trying to move its joints. map_keyboard() function captures the key input and moves the joint as explained above.
