Hand Grips: Power vs. Precision

Gripping Behavior

• Grip type is the interface between a person's hand and an object, affecting force generation and injury risk.

Hand Grips

• Grasps can be either power grip, or precision grip

Power Grip

• An object needs to be held forcefully and moved by more proximal muscles
• Cylindrical grip involves fingers flexed around an object with the thumb on the opposite side; used for gripping tools
• Spherical grip has fingers and thumb together around an object, like grabbing an apple or doorknob
• Hook grip involves flexing the second through fifth fingers around an object; the thumb is extended and not involved, and requires thumb or median nerve ability

Precision Grip

• An object is manipulated with fingers
• Pad to pad (Pinch grip) involves the thumb and one finger gripping
• Tip-to-tip or pincer grip uses the tip of the thumb against the tip of a finger, like picking up a coin and is difficult with long fingernails
• Lumbrical or plate grip has the MCP and PIP joints flexed and the DIP extended, using the thumb to oppose and hold something horizontal like a plate; the lumbricals flex the MCP joint

Medical Robot Design

• Medical robots are complex systems with an articulated and motorized mechanical structure, a human-machine interface (HMI), instruments, electronic components, and a software controller
• Elements are integrated to achieve daily medical tasks under optimal safety conditions
• Procedures occur in constrained, not fully structured environments, within a limited workspace inside and/or outside a patient's body, in collaboration with medical staff

Gesture of Practitioner

• A main design step is characterizing the gesture of the practitioner to determine system specifications like workspace, velocity, effort, or precision

Reconstructive Surgery Example

• The feasibility study for an assistant robot for skin harvesting in reconstructive surgery used the Dermarob robot
• The dermarob is equipped with a dermatome (a kind of razor) with an electric motor to vibrate the blades and perform skin incision
• The instrument used a force sensor (ATI gamma force sensor 130 N / 10 Nm, 6 components) and a cable actuated velocity sensor (ASM Sensor)

Kinematic Choices for Robot Design

• "Conventional" serial kinematics manipulator arms
• Parallel architecture manipulator arms
• Hybrid architecture
• Architecture with remote center of motion
• Symbolic representation involves two kinds of joints: revolute (rotational, represented by a cylinder) and prismatic (translational, represented by a cube or prism)

Serial Kinematics

• Industrial robots use serial kinematic robots extensively, which are non-redundant
• Two architectures are "anthropomorphic" and "SCARA" robots

Anthropomorphic Robots

• Anthropomorphic robots are common in the automobile industry (welding, painting) and consist of a "carrier" and a "wrist", each with three degrees of freedom (dof)
• The carrier is responsible for positioning the wrist's center, while the wrist gives the tool its orientation
• Caspar is an example of robots used for orthopedic surgeries, Hippocrates developed a robotic system to assist doctors when they are moving ultrasonic probes and pathfinder is an image-guided robot

SCARA Robots

• SCARA robots are used in manipulation industries and are four dof robots
• Two pivot joints and a prismatic joint place a point in space, and a third pivot guides the tool around a single axis
• ROBODOC is used for orthopedic surgeries and PADyC in cardiac surgeries and limits the instrument motions with respect to a pre-defined surgical plan
• SCARA workspace is a cylinder vs anthropomorphic robots which is a sphere
• SCARA arm and forearm movements are more predictable due to being constrained in a plane
• The kinematic models of the SCARA robot are simpler
• Gravity affects almost all its joints are sensitive to it for an anthropomorphic robot, while the first three pivot joints of the SCARA robot are not affected by it

Parallel Architecture

• Parallel robots have several kinematic chains linking the base to the end-effector, unlike serial robots
• In a parallel robot, the end-effector connects to the base through interconnected links
• Parallel robots have at least two "legs" or "arms", and most joints are not actuated
• Passive joints have several degrees-of-freedom (DOFs) like spherical, universal, and planar joints
• Telescoping-leg hexapods are common in motion simulators, and Delta robots are used for rapid pick-and-place
• They have a good "payload to robot weight" ratio, high velocities and accelerations, and good mechanical stiffness
• Models are easy to write but difficult to resolve, often requiring direct geometric models as high-order polynomials
• The robots tend to be tricky to calibrate
• Parallel robots have a less favorable ratio between footprint and workspace, resulting in a significant bulk within the operative area
• SurgiScope is a 3 dof "Delta" kinematics system for translations with a conventional wrist for rotations, enabling movement of a large load (operating microscope)
• Spine Assist is a "hexapod"-like robot with 6 dof, designed to be clamped onto the spine to perform operations such as pedicular screw placement with high accuracy and its high stiffness

Hybrid Architecture

• "Hybrid" architectures include several kinematic chains in parallel that can have serial kinematics with several actuators
• Solutions offer good stiffness and interesting workspace with regard to the orientation of the tools
• CT-BOT robot can perform biopsies under a CT scanner