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# Contigutive: requiring direct contact for adhesion to take place (such as glue, [[surface tension]], or freezing).
These categories describe the physical effects used to achieve a stable grasp between a gripper and the object to be grasped.<ref>{{cite journal | last1 = Fantoni | first1 = G. | last2 = Santochi | first2 = M. | last3 = Dini | first3 = G. | last4 = Tracht | first4 = K. | last5 = Scholz-Reiter | first5 = B. | last6 = Fleischer | first6 = J. | last7 = Lien | first7 = T.K. | last8 = Seliger | first8 = G. | last9 = Reinhart | first9 = G. | last10 = Franke | first10 = J. | last11 = Hansen | first11 = H.N. | last12 = Verl | first12 = A. | year = 2014 | title = Grasping devices and methods in automated production processes | url = http://orbit.dtu.dk/en/publications/grasping-devices-and-methods-in-automated-production-processes(ec5df835-f404-40c9-afd3-c2fb2ea6f4aa).html| journal = CIRP Annals - Manufacturing Technology | volume = 63 | issue = 2| pages = 679–701 | doi = 10.1016/j.cirp.2014.05.006 | url-access = subscription }}</ref>
Industrial grippers may employ mechanical, suction, or magnetic means. Vacuum cups and electromagnets dominate the automotive field and metal sheet handling. [[Bernoulli grip|Bernoulli grippers]] exploit the airflow between the gripper and the part, in which a lifting force brings the gripper and part close each other (using [[Bernoulli's principle]]). Bernoulli grippers are a type of contactless grippers; the object remains confined in the force field generated by the gripper without coming into direct contact with it. Bernoulli grippers have been adopted in photovoltaic cell handling, [[silicon wafer]] handling, and in the textile and leather industries.
Other principles are less used at the macro scale (part size >5mm), but in the last ten years, have demonstrated interesting applications in micro-handling. Other adopted principles include: Electrostatic grippers and van der Waals grippers based on electrostatic charges (i.e. [[van der Waals' force]]); capillary grippers; cryogenic grippers, based on a liquid medium; ultrasonic grippers; and laser grippers, the latter two being contactless-grasping principles.
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=== Gripper mechanism ===
A common form of robotic grasping is [[robotic force closure|force closure]].<ref name="fub20140320">{{cite book | last1=Lynch | first1=Kevin M. | last2=Park | first2=Frank C. | title=Modern robotics: Mechanics, planning, and control | date=2017-05-25 | publisher=Cambridge University Press | isbn=978-1-107-15630-2 | oclc=983881868}}</ref><!-- there appears to be no WP article on force closure so leaving a link to source the concept. -->
Generally, the gripping mechanism is done by the grippers or mechanical fingers. Two-finger grippers tend to be used for industrial robots performing specific tasks in less-complex applications.{{citation needed|date=March 2014}} The fingers are replaceable.{{citation needed|date=March 2014}}
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Here, the value of <math>\,g</math> should be taken as the acceleration due to gravity and <math>\,a</math> the acceleration due to movement.
For many physically interactive manipulation tasks, such as writing and handling a screwdriver, a task-related grasp criterion can be applied in order to choose grasps that are most appropriate to meeting specific task requirements. Several task-oriented grasp quality metrics<ref>{{cite journal |title=Grasp planning to maximize task coverage |journal=The International Journal of Robotics Research|volume=34|issue=9|pages=1195–1210|doi=10.1177/0278364915583880|year=2015 |last1=Lin |first1=Yun |last2=Sun|first2=Yu|s2cid=31283744 }}</ref> were proposed to guide the selection of a good grasp that would satisfy the task requirements.
== Tools ==
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== See also ==
* [[Grapple (tool)]]
* [[Prehensility]]
* [[Tongs]]
* [[Shadow Hand]]
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