parallel_single_servo_controller.py
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00001 #!/usr/bin/env python
00002 
00003 """
00004   parallel_single_servo_controller.py - controls a single-servo parallel-jaw gripper
00005   Copyright (c) 2011 Vanadium Labs LLC.  All right reserved.
00006 
00007   Redistribution and use in source and binary forms, with or without
00008   modification, are permitted provided that the following conditions are met:
00009       * Redistributions of source code must retain the above copyright
00010         notice, this list of conditions and the following disclaimer.
00011       * Redistributions in binary form must reproduce the above copyright
00012         notice, this list of conditions and the following disclaimer in the
00013         documentation and/or other materials provided with the distribution.
00014       * Neither the name of Vanadium Labs LLC nor the names of its 
00015         contributors may be used to endorse or promote products derived 
00016         from this software without specific prior written permission.
00017   
00018   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
00019   ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
00020   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
00021   DISCLAIMED. IN NO EVENT SHALL VANADIUM LABS BE LIABLE FOR ANY DIRECT, INDIRECT,
00022   INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
00023   LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA,
00024   OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
00025   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
00026   OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
00027   ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
00028 """
00029 
00030 import roslib; roslib.load_manifest('arbotix_controllers')
00031 import rospy, tf
00032 import thread
00033 
00034 from std_msgs.msg import Float64
00035 from sensor_msgs.msg import JointState
00036 from math import asin
00037 
00038 class ParallelGripperController:
00039     """ A simple controller that operates a single servo parallel jaw gripper. """
00040     def __init__(self):
00041         rospy.init_node("gripper_controller")
00042 
00043         # TODO: load calibration data. Form: opening->servo angle
00044         self.calib = { 0.0000 : 1.8097, 0.0159: 1.2167, 0.0254 : 0.8997, 0.0381 : 0.4499, 0.042 : 0.1943 }
00045         #self.calib = { 0.0000 : 866, 0.0159: 750, 0.0254 : 688, 0.0381 : 600, 0.042 : 550 }
00046 
00047         # parameters
00048         self.min = rospy.get_param("~min", 0.0)
00049         self.max = rospy.get_param("~max", 0.042)
00050         self.center = rospy.get_param("~center", 512)
00051         self.invert = rospy.get_param("~invert", False)
00052         
00053         # publishers
00054         self.commandPub = rospy.Publisher("gripper_joint/command", Float64)
00055         self.br = tf.TransformBroadcaster()
00056     
00057         # current width of gripper
00058         self.width = 0.0
00059 
00060         # subscribe to command and then spin
00061         rospy.Subscriber("~command", Float64, self.commandCb)
00062         rospy.Subscriber("joint_states", JointState, self.stateCb)
00063         
00064         r = rospy.Rate(15)
00065         while not rospy.is_shutdown():
00066             # output tf
00067             self.br.sendTransform((0, -self.width/2.0, 0),
00068                                    tf.transformations.quaternion_from_euler(0, 0, 0),
00069                                    rospy.Time.now(),
00070                                    "gripper_left_link",
00071                                    "gripper_link")
00072             self.br.sendTransform((0, self.width/2.0, 0),
00073                                    tf.transformations.quaternion_from_euler(0, 0, 0),
00074                                    rospy.Time.now(),
00075                                    "gripper_right_link",
00076                                    "gripper_link")
00077             r.sleep()
00078 
00079     def getCommand(self, width):
00080         """ Get servo command for an opening width. """
00081         keys = self.calib.keys(); keys.sort()   
00082         # find end points of segment
00083         low = keys[0]; 
00084         high = keys[-1]
00085         for w in keys[1:-1]:
00086             if w > low and w < width:
00087                 low = w
00088             if w < high and w > width:
00089                 high = w
00090         # linear interpolation
00091         scale = (width-low)/(high-low)
00092         return ((self.calib[high]-self.calib[low])*scale) + self.calib[low]
00093 
00094     def getWidth(self, command):
00095         """ Get opening width for a particular servo command. """
00096         reverse_calib = dict()
00097         for k, v in self.calib.items():
00098             reverse_calib[v] = k
00099         keys = reverse_calib.keys(); keys.sort()
00100         # find end points of segment
00101         low = keys[0]
00102         high = keys[-1]
00103         for c in keys[1:-1]:
00104             if c > low and c < command:
00105                 low = c
00106             if c < high and c > command:
00107                 high = c
00108         # linear interpolation
00109         scale = (command-low)/(high-low)
00110         return ((reverse_calib[high]-reverse_calib[low])*scale) + reverse_calib[low]
00111 
00112     def commandCb(self, msg):
00113         """ Take an input command of width to open gripper. """
00114         # check limits
00115         if msg.data > self.max or msg.data < self.min:
00116             rospy.logerr("Command exceeds limits.")
00117             return
00118         # compute angle
00119         self.commandPub.publish( Float64( self.getCommand(msg.data) ) )
00120 
00121     def stateCb(self, msg):
00122         """ The callback that listens for joint_states. """
00123         try:
00124             index = msg.name.index("gripper_joint")
00125         except ValueError:
00126             return
00127         self.width = self.getWidth(msg.position[index])
00128 
00129 if __name__=="__main__": 
00130     try:
00131         ParallelGripperController()
00132     except rospy.ROSInterruptException:
00133         rospy.loginfo("Hasta la Vista...")
00134         


arbotix_controllers
Author(s): Michael Ferguson
autogenerated on Wed Aug 26 2015 10:44:22