Sensors play an important role in the operation of a robotic system, both within the robot itself and in its interactions with other components, parts, and environment.
Analog devices that are available for motion sensing include resolvers, potentiometers, linear-variable differential transformers (LVDT), tachometers, accelerometers, Hall-effect sensors, and eddy current sensors.
Pulse-generating (or digital) motion transducers such as optical encoders (both absolute and incremental) and binary (limit) switches are also commonly used. Force, torque, and tactile (distributed touch) sensors are also quite useful in robotic tasks. They may employ piezoresistive (including strain-gauge), piezoelectric, and optical principles.
Cameras (linear or matrix, chargecoupled- device or CCD) and optical detectors with structured lighting such as lasers that can generate either single or multiple light stripes may be used in tasks such as object detection, recognition, and sensing of geometric features.
The end effector or mechanical hand plays an important role in robotic manipulation. Consequently, the control problem of multifingered mechanical hands has received much attention. Control of a robotic hand is facilitated through proper understanding and modeling of the associated system.
Here, contact analysis between a robotic finger and an object is of interest. Characteristics and phenomena such as contact friction, flexibility of finger and the object, material properties and nonelastic behavior have been studied in this context. An innovative robotic gripper has been designed, developed, and tested by us.
In the present section, the key features of the gripper are outlined. Next, an analysis of contact mechanics and kinematics of the gripper is presented.
This will form an analytical model, which has been used in computer simulation and also in design development of the gripper. What is presented here may be used as a typical example in modeling, analysis, and design of robotic grippers.
In theory, a gripper may contain any number of fingers, and each finger may consist of any number of links. In the present design, each finger, not each link joint, is driven by a single actuator.
Actuation begins with the link that is directly coupled to the particular motor. When this link makes contact with the object, subsequent actuation will result in overloading of the corresponding joint.
An innovative mechanical switch causes the next joint in that finger to be actuated. This actuation sequence will continue for all the joints of the finger, being driven by a single motor, until the mechanically-preset load thresholds of the joints are reached. Mechanical switching uses friction between two rotating members, one being in internal contact with the other.
The level of frictional force/torque is set by adjusting the normal reaction force. When the transmitted torque is less than the frictional torque threshold, the two members rotate as one integral unit.
When the torque to be transmitted exceeds this limit, that is, when the joint is overloaded, a relative motion between the two members will result.
This motion will actuate the next joint in the finger, the torque at the current joint being decided by the limiting friction.
A picture of the gripper prototype.
The particular gripper design has several advantages.
Notably, it uses fewer number of actuators than it has degrees of freedom, thereby providing quantifiable savings in weight,