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:
As compared to manual handling, the use of positioning equipment can provide the following benefits [Modern Materials Handling, Sept. 1993]:
- raise the productivity of each worker when the frequency of handling is high,
- improve product quality and limit damage to materials and equipment when the item handled is heavy or awkward to hold and damage is likely through human error or inattention, and
- reduce fatigue and injuries when the environment is hazardous or inaccessible.
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
2. Lift/Tilt/Turn Table
Used when positioning involves the lifting, tilting, or turning of a loadCan 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
3. Dock Leveler
Used at loading docks to compensate for height differences between a truck bed and the dock4. Ball Transfer Table
Used in conveyor systems to permit manual transfer to and from machines and conveyors and between different sections of conveyorsSince loads are pushed on the table, ball friction limits the maximum load weight to 600 lbs.
5. Rotary Index Table
Used for the synchronous transfer of small parts from station to station in a single workcenterCircular 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
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)
7. Air Film Device
Used to enable precision positioning of heavy loadsSometimes 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
8. Hoist
Used for vertical translation (i.e., lifting and lowering) of loadsFrequently attached to cranes and monorails to provide vertical translation capability
Can be operated manually, electrically, or pneumatically
9. Balancer
Mechanism used to support and control loads so that an operator need only guide a balanced ("weightless") load, thus providing precision positioningCan also be attached to hoists and manipulators
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 control10(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)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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