The Humanoid Hand Project
All robots need ways to interact with their target environment. Our robotic system, ISAC, is targeted to aid elderly or disabled people in their home. ISAC will be called on to help perform tasks such as feeding, using the phone, and manipulating household objects. ISAC's 6DOF arms will thus need end-effectors that will allow it to interact in a human's world. The natural choice is an anthropomorphic hand design since all objects in the environment are designed with human manipulation in mind. I am developing a robotic hand which allows human-like grasping of objects freeing the user from restricting his environment and allowing the development of algorithms to parallel our own methods for grasping.
- Anthropomorphic design
- Human-like grasping (spoon,cup,phone,ball,marker,etc.)
- Simple design and operation
- Safe operation near humans
The hand utilizes a Watt 6-Bar Linkage for coupling actuator motion for both the distal and proximal joints of a single finger. This allows one actuator to emulate the joint ranges of the proximal and distal joints of the human phalange.
The initial hand design will be limited to five force sensitive resistors (FSRs). Each finger's inside distal pad will contain an FSR that varies its resistance based on the force exerted on its surface. Additionally, one FSR will reside in the palm.
These FSRs provide the hand with feedback from its environment. One reason for this is to simplify the control of the hand. A priori knowledge of the obstacle to be grasped will allow us to set a force threshold and determine a grasping strategy to successfully obtain the object. A behavior-based implementation will demonstrate this strategy.
The backside of the palm will contain the circuitry for the FSRs. A 20-pin DIN connector will interface this circuit to the PC card's 16-bits of digital I/O. 3 bits of digital output will select an octal latch or an 8-bit A/D converter for driving the 8-bits of digital input to the PC card's I/O. An analog input will also be selected on the 8-channel, 8-bit A/D converter. Future expansion will be facilitated by the addition of octal latches for simple tactile information. 3 channels of analog input will also be available.
Reflexive Grasping: A grasping behavior is implemented based on the first grasping patterns of the neonates which are driven by sensory inputs to the palmar surface. Put simply, when a force is perceived at the palm's force sensitive resistor that exceeds some threshold, the fingers will close in an attempt to grasp the object.
Force-Based Grasping: This is a high level behavior used to grasp objects based on a priori knowledge. A grasping force and a simple boolean command (OPEN,CLOSE) are given to this behavior. If the fingers close at the given grasping force without registering any forces, this behavior issues an error message that is relayed to higher-level agents of the system.