Material Handling Equipment

II. Positioning Equipment

Positioning equipment is used to handle material at a single location so that the material is in the correct position for subsequent handling, machining, transport, or storage. Unlike transport equipment, positioning equipment is usually used for handling at a single workplace. Material can also be positioned manually using no equipment. The major types of positioning equipment are:

  1. Manual (no equipment)
  2. Lift/tilt/turn table
  3. Dock leveler
  4. Ball transfer table
  5. Rotary index table
  6. Parts feeder
  7. Air film device
  1. Hoist
  2. Balancer
  3. Manipulator
    1. Rigid-link manipulator
    2. Articulated jib crane manipulator
    3. Vacuum manipulator
  4. Industrial robot

As compared to manual handling, the use of positioning equipment can provide the following benefits [Modern Materials Handling, Sept. 1993]:

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1. Manual (No Equipment)

Material can be positioned manually using no equipment

Under ideal circumstances, maximum recommended weight for manual lifting to avoid back injuries is 51 lbs.

Recommendation based on NIOSH (National Institute for Occupational Safety and Health) 1994 Lifting Equation, which uses six multipliers to reduce maximum recommended weight for less than ideal lifting tasks

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2. Lift/Tilt/Turn Table

Used when positioning involves the lifting, tilting, or turning of a load

Can be used to reduce or limit a worker’s lifting and/or reaching motions

Pallet load levelers are lift and turn tables used in manual palletizing to reduce the amount of bending and stooping involved with manually loading a pallet by combining a lifting and turning mechanism with a device that lowers the table as each layer is completed so that loading always takes place at the optimal height of 30 inches

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3. Dock Leveler

Used at loading docks to compensate for height differences between a truck bed and the dock

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4. Ball Transfer Table

Used in conveyor systems to permit manual transfer to and from machines and conveyors and between different sections of conveyors

Since loads are pushed on the table, ball friction limits the maximum load weight to 600 lbs.

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5. Rotary Index Table

Used for the synchronous transfer of small parts from station to station in a single workcenter

Circular table rotates in discrete intermittent steps to advance parts between stations located along its perimeter

Since each part moves between stations at the same time, it is difficult to put buffers between stations

Different from conveyors used as in-line indexing machines, where linear transfers can take place between multiple workcenters separated by long distances, since a rotary index table is restricted to circular transfers with a single compact workcenter

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6. Parts Feeder

Used for feeding and orienting small identical parts, particularly in automatic assembly operations [13]

Motion of parts in a random pile channeled so that each part automatically assumes a specified orientation, where the symmetries of a part define its possible orientations

Motion can be imparted through vibration, gravity, centrifugal force, tumbling, or air pressure

In a vibratory bowl feeder, the most versatile type of parts feeder, parts are dumped into a bowl and then move vibrate uphill along a track towards an outlet, where rejected parts fall off the track and are recycled

Parts feeders can be used to provide inspection capabilities with respect to the shape and weight of parts (e.g., the coin feeder of a vending machine)

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7. Air Film Device

Used to enable precision positioning of heavy loads

Sometimes referred to as "air pallets"

Can be used in place of cranes and hoists

Thin film of compressed (10–50 psi) air used to float loads of up to 300,000 lbs. so that a horizontal push of 1 lb. can move 1000 lb. load; floating action enables load to rotated or translated in any direction in the horizontal plane

Requires a smooth floor surface against which air streams underneath the device can push

Can be used in warehousing as the mechanism to convert stationary racks into sliding racks

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8. Hoist

Used for vertical translation (i.e., lifting and lowering) of loads

Frequently attached to cranes and monorails to provide vertical translation capability

Can be operated manually, electrically, or pneumatically

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9. Balancer

Mechanism used to support and control loads so that an operator need only guide a balanced ("weightless") load, thus providing precision positioning

Can also be attached to hoists and manipulators

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10. Manipulator

Used for vertical and horizontal translation and rotation of loads

Acting as "muscle multipliers," manipulators counterbalance the weight of a load so that an operator lifts a small portion (1%) of the load’s weight

Can be powered manually, electrically, or pneumatically

Manipulator’s end-effector can be equipped with mechanical grippers, vacuum grippers, electromechanical grippers, or other tooling

Manipulators fill the gap between hoists and industrial robots: they can be used for a wider range of positioning tasks than hoists and are more flexible than industrial robots due to their use of manual control

10(a) Rigid-Link Manipulator

Although similar in construction, a rigid-link manipulator is distinguished from an industrial robot by the use of an operator for control as opposed to automatic computer control

10(b) Articulated Jib Crane Manipulator

Extends a jib crane’s reaching capability in a work area through the use of additional links or "arms"

10(c) Vacuum Manipulator

Provides increased flexibility because rigid links are not used (vacuum, rigid-link, and articulated jib crane manipulators can all use vacuum gripper end-effectors)

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11. Industrial Robot

Used in positioning to provide variable programmed motions of loads

"Intelligent" industrial robots utilize sensory information for complex control actions, as opposed to simple repetitive "pick-and-place" motions

Industrial robots also used for parts fabrication, inspection, and assembly tasks

Consists of a chain of several rigid links connected in series by revolute or prismatic joints with one end of the chain attached to a supporting base and the other end free and equipped with an end-effector

Robot’s end-effector can be equipped with mechanical grippers, vacuum grippers, electromechanical grippers, welding heads, paint spray heads, or any other tooling

Although similar in construction, an industrial robot is distinguished from a manipulator by the use of programmed control logic as opposed manual control

Pick-and-place industrial robots used as automatic palletizers

Mobile robots similar in construction to free-ranging AGVs

Can be powered manually, electrically, or pneumatically

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Last modified: September 30, 1999