Conveyors as workstations

Conveyors can serve as the foundation for a workstation equivalent to a workbench.  For the most part, there is no difference in approach between the design setup of a bench workstation and a conveyor workstation.  However, there are some special issues that must be taken into account:

• Tools and materials cannot be placed directly on the conveyor
• Manipulating items on a conveyor may involve special considerations
• Conveyors cannot be adjusted for individual employee height when more than one person works on the same line

Ideas and Options

Placement of tools and materials

Car assembly — Materials distant from point of use

Unlike a standard workbench, tools and materials cannot be placed directly on the conveyor.  In the car assembly plant shown above the conveyor system is quite large.  Materials that are needed must be placed off line, which can require considerable walking (perhaps unavoidable, but an issue to evaluate).

Material containers on table under the overhead conveyor	Tools and parts containers adjacent to conveyor line

Fortunately, for smaller conveyor lines, it is usually much easier to place equipment like racks and tools adjacent to the point of use.  With some careful thinking, there may not be much difference between the setup of a conveyor workstation and that of a standard workbench.

Rotators

Product on conveyor line	Rotator turning product 180°	Rotator without product

Rotating a heavy item on a standard workbench can easily be accomplished with an inexpensive turntable or other similar options.  However, rotating on a conveyor line can be another matter.  In the sequence of photos above, a turntable on a powered cylinder has been incorporated into the line.  When the product moving down the line reaches the turntable, it lifts up and rotates 180°, thus eliminating long reaches to assemble on the opposite side of the line.

Tilters

Before	After

The example above shows how a tilter can be integrated into a conveyor line.  A powered cylinder on one side of the line lifts the product.  A backstop is at the far end to prevent the product from sliding backward.

Adjustable height conveyors

Up position	Down position (with product)

It is common for a section of a conveyor line to be placed on a powered lift to enable work on both upper and lower portions of a large product.  In this sense, there is no difference between a conveyor workstation and a standard workbench, but sometimes this option is overlooked when conveyor lines are installed

Low	Medium	High

The height of an entire conveyor line can be adjusted for products of different heights.  Note in the photos above that the system uses (a) a powered scissors lift and (b) a sawhorse-type support with a flip-down upper section for use when the conveyor is in the medium and high positions.

Upenders

Two examples of upenders integrated into a conveyor line

Many times, is it necessary to change the position of large products from one side to another.  Upenders can easily be integrated into conveyor lines for this purpose.

Knee Clearance

Conveyor sides block knees	Pressure point

Work surfaces should normally be as thin as possible in order to provide good knee clearance (see clearance).  However, conveyors usually need thick sides in order to support the load on the conveyor and belt conveyors need space for the full loop of the belt.  Consequently, the sides of the conveyor can inhibit knee clearance.  Sometimes these problems can be minimized with thinner or tighter belts, plus there are alternative ways to provide sufficient stability to the conveyor.  Nonetheless, providing proper clearance can be a problem that is difficult to resolve.

Multiple employees on same conveyor line

Short and tall working on overhead monorail

When more than one employees works on the same conveyor, it can be difficult to provide optimal working height.  Sometimes it is possible to provide variable height standing platforms, but employees must always stay in the same location to do so.  More commonly, employees need to move up and down the line, which makes platforms infeasible.

The same problem can occur when multiple employees work on the same workbench.  However, typically it is much easier to provide height adjustment for benchwork.  A moving conveyor line creates a bigger challenge.

Orientation to conveyor

In the previous examples, employees work directly on the conveyor. However, it is common to pull a product from a moving conveyor for work at a machine or separate workstation. This situation raises the issue of the best orientation of the employee to the moving line.

Poor: Workstation facing away from line	Best: Workstation perpendicular to the line, facing flow

The photo above left shows an awkward layout, where a machine is located away from the line, facing the opposite direction. This orientation crates extra motions and long reaches. Above right is a much better layout. The machine is adjacent and perpendicular to the line. The employee is able to easily see upstream to the parts that are coming. Additionally the reach is shorter.

Note: The workstation above right can be improved in two additional ways: (1) raising the conveyor to be exactly level with the fixture in the machine, and (2) adding a small slide to eliminate the need to pick up the product.

OK: Parallel to line (facing line)	Better: Perpendicular to line

It can sometimes be acceptable to orient a workstation parallel with the line (facing the line) if the items are small and the forward reach is minimal. However, in most cases, the perpendicular layout is better.

Moving line – general adaptations

Model T Ford assembly, Highland Park, MI

Working on any object that is moving can be difficult in any circumstance.  When the job is highly repetitive, many more problems arise.  Indeed, assembly line work has been a symbol of the negative side of manufacturing since its inception.

One strategy for improving assembly line work is to incorporate stationary work within the line.  The following are several options:

• Slide the product off the moving conveyor for work, then push it back onto the line.
• Enlarge the jobs, so that each employee performs more tasks, and thus enables the product to be held stationary longer.
• Index the line so that the entire line stops while the work is performed, then advances to move the product to the next position (the cycle time of all tasks must be highly balanced).
• Make sub-assemblies off line, then add to the product on the moving line.
• Space products closer together (if possible) and slow the line.  Thus, throughput can remain the same even if the line runs slower.  Sometimes expanding the length of the conveyor can enable closer spacing of the products.