IN RECENT YEARS, MANUFACTURERS AND RETAILERS HAVE MADE extensive investments in automated material handling systems inside and around warehouses and distribution centers. Contributing factors are increased demand from online businesses, the need for increased productivity in the midst of a challenging labor market, and worker safety mandates.
In the warehouse environment, pick and place robots are used at transfer points, such as cartoning, palletizing, sorting, and order picking. Typically, encoders are employed to aid the infeed of items to the robot via a conveyor, with encoder signals used for speed information in conjunction with a vision sensor. Encoder placement and specification should align with the typical conveyor feedback options for wheeled, shaft-mount, and thru-bore types.
A mainstay of warehouse operations for decades, forklifts are being fitted with added sensors, including encoders, to aid with productivity and worker safety. More recent entrants to the warehouse ecosystem, autonomous mobile robots (AMRs), and automated guided vehicles (AGVs) must accomplish a variety of complex tasks in dynamic operating environments. To meet performance objectives safely and efficiently, these vehicles rely on encoders for steering, propulsion, and storage and retrieval functions.
For drive motor applications in AGVs and AMRs, encoders with compact housings are preferred due to the space constraints in most mobile platforms. With long-duty cycles, heavy loads, and frequent acceleration and braking, encoders with high-temperature ratings (100° C or higher) are a must. Thru-bore options are generally preferred.
For AGV steering applications, the encoder may be fixed to the motor that operates the steering mechanism, the steering shaft, or both. Depending on the control system, incremental or absolute encoders can be applied.
Both human-operated and autonomous forklifts can benefit from encoder feedback. For controlling vertical positioning of the forks, a draw wire encoder can be applied to the tower as either primary or secondary feedback in combination with other sensors. Extendable forks can also use draw wire encoders on the horizontal axis.
Autonomous vehicles in warehouses and other facilities must adhere to safety standards due to the inherent hazards of operating heavy mobile equipment alongside human workers. To comply with functional safety requirements in AMR and AGV applications, redundant sensor feedback is necessary. Two separate sensing methods are preferred, such as both an optical and a magnetic encoder in a combination device. Functional safety requirements are challenging today’s system designers to identify sensors that are both safety compliant and cost-effective.
Automated Storage and Retrieval systems (AS/RS) are important features of the modern warehouse or distribution center. The ability to quickly and accurately locate and transport items with little to no human intervention has enabled facility operators to increase efficiency and productivity. The automated devices that are critical components in these systems benefit from encoder feedback for accuracy and reliability.
Common formats for AS/RS are carousels, vertical lifts, gantry type, and grid-based mobile robots. Encoders can be applied to gear motors or other drive motors for basic speed and direct feedback. For more precise control, absolute encoders can be employed to track specific locations of rotating or track-mounted carousel systems.
For AS/RS lift systems that employ an extractor/inserter device to store or retrieve bins, draw wire encoders can provide accurate linear measurement. Preference should be given to an industrial-duty draw-wire encoder with accurate linearity (+/- 0.05% or better) and a durable spring retraction system.
When an AS/RS system pulls bins or contents from a storage area, a conveyor may be used for transporting the items to the next station or work area. The typical encoder feedback options discussed previously can be employed in such cases. Because many AS/RS facilities are designed with networked control and monitoring systems, absolute encoders with network protocols may be required.
Pick and place robots rely on conveyor speed and motion feedback for precise timing
Typical encoder placement on an AMR
