Pusher and diverter sorters are conveyor-based machines that move packages from a main line into selected side lanes. They are used in warehouses, parcel hubs, airports, and distribution centers where many items must be routed quickly and accurately. The physics of these systems connects motion, timing, friction, sensors, and actuator force.
Understanding how they work helps students see how mechanics and control systems solve real logistics problems.
A package is first identified by a scanner or sensor, then a controller predicts when it will reach a sorting point. At the correct moment, a pusher arm or angled diverter applies a sideways force that changes the package path without stopping the conveyor. The design must match belt speed, package mass, friction, spacing, and lane geometry so items do not collide or tip.
Good sorter performance depends on both mechanical reliability and precise timing.
Key Facts
- Throughput rate = number of sorted packages / time
- Package travel time to sorter = distance to sorter / conveyor speed
- Required lateral acceleration can be estimated with a = 2d / t^2
- Sideways force needed from an actuator is F = ma
- Static friction limit is F_f,max = μ_s N, where N is the normal force
- Minimum package spacing = conveyor speed × control response time
Vocabulary
- Pusher sorter
- A sorting device that uses a moving arm or plate to push selected packages sideways off a main conveyor.
- Diverter sorter
- A sorting device that uses angled wheels, belts, gates, or rollers to guide selected packages into another lane.
- Actuator
- A mechanical device, often pneumatic, electric, or hydraulic, that produces controlled motion or force.
- Photoelectric sensor
- A sensor that detects the presence or position of an object by using a beam of light.
- Throughput
- The number of items a system can process in a given amount of time.
Common Mistakes to Avoid
- Using belt speed as the sideways speed, which is wrong because the package has separate motion along the conveyor and across the conveyor.
- Ignoring package spacing, which is wrong because a sorter needs time to identify one item, actuate, and reset before the next item arrives.
- Assuming heavier packages always sort the same way as lighter packages, which is wrong because greater mass requires greater force for the same sideways acceleration.
- Forgetting friction limits, which is wrong because too little friction can make a package slide unpredictably while too much friction can resist the desired sideways motion.
Practice Questions
- 1 A conveyor moves at 1.5 m/s. A package is detected 3.0 m before a pusher. How many seconds after detection should the controller trigger the pusher if there is no delay?
- 2 A 4.0 kg carton must be moved sideways 0.50 m in 0.40 s. Estimate the required lateral acceleration using a = 2d / t^2, then find the required sideways force using F = ma.
- 3 A warehouse changes from small rigid boxes to tall, lightweight cartons. Explain why the sorter settings or hardware might need adjustment even if the conveyor speed stays the same.