envelope stuffer


Requested Project

Assist a consumer, who has limited fine motor skills, to place letters into envelopes.  Russ Schuchmann has volunteered for this project.

Design Notes

Envelope stuffer Project #329 for Options of Linn County  - Designer,  Russ Schuchmann

Options of Linn County provides services for certain clients where envelopes are stuffed with the mailing materials and prepared for mailing.  This is a task that requires reasonably good motor skills to perform in an expeditious manner.  Consequently the thrust of this project is to provide a device that will perform the task through a series of guided motions that can be done with limited motor skills.  The series of tasks is as follows:

1. Open the envelope flap to prepare the envelope to receive the contents
2. Prop open the envelope opening to provide a good target to receive the contents
3. Provide a guided chute that will allow the contents to easily slide into the envelope

To facilitate these tasks the envelope stuffer starts with a flat bed or platen with a well-defined area to place the envelope.  Boundaries of the area locate the envelope for the sequence of operations that follow.  The platen is fitted with a slide that can move the envelope back and forth as the slide is moved manually by pushing or pulling on a lever having a knob to grasp.  The envelope motion is constrained by tracks on the slide (small ball-bearing drawer slides) to produce a forward or backward motion of the envelope, while the range of forward/backward motion is limited to that which is required.  Figure 1 provides an overall view of this platen and its auxiliary parts.

The end of the platen is sawed at a 30 degree angle with respect to the top surface of the platen.  A second cut at the same angle is made across the platen, but only partially through the platen material.  Figure 2 includes a side view of these cuts. The remaining material left after the second cut supports a tray (when it is in the lowered position) that is used to hold the insert material, while space between the bottom of the tray and the second partial cut forms a slot that will direct the flap end of the envelope downward as it is pushed into the slot by the aforementioned slide.  When the flap end of the envelope is bent down the flap will raise up away from the envelope and remain partially raised as the envelope is withdrawn from the slot by the slide moving backward.  

As the envelope was being pushed forward into the slot it had passed beneath a small rod spanning the width of the platen (This rod is identified in Figure 3).  When withdrawn from the slot the body of the envelope again passes beneath the rod, however, the flap of the envelope, now raised, catches on the rod and as the envelope is withdrawn further the flap is folded back to an open position.  So, this point the flap is out of the way for the insertion of the materials that will go into the envelope.

The materials that go into the envelope are now placed into the insert tray (See Figure 5).  This tray has sides and a back (the lower end of the tray which is perched at a 30 degree angle) that holds the insert in alignment with a path to enter the envelope.  This tray is mounted to a pivot mechanism (see Figure 2) that allows the tray to swing from its rest position to an insert position that makes a ramp downward to the mouth of the envelope.  Figure 7 provides a view of the Plexiglas tray mounts and the pivot point. The tray is made from brass which provides a smooth surface on which to slide the insert materials.

Another important element of the tray is a thin set of metal blades that are mounted to a rod which spans the sides of the front end of the insert tray and is about 3/8? above the tray bed.  (See Figure 4 for a view of these blades) These blades are oriented and guided by a cam mechanism such that, as the tray is swung into the upright position, they will enter the mouth of the envelope and prop it open.  Further, the blades form a channel between themselves and the bottom of the tray which forces the insert to glide into the mouth of the envelope when it is pushed manually down the ramp formed by the tray in upright position.

Once the insert has been slid into the envelope the insert tray can be lowered and the envelope removed, now containing the insert materials.  Thumb slots visible in Figure 4 are provided on each side of the platen so the envelope can be easily grasped from either side for removal.

There are additional details of the construction that are important to successful application of the plan above.  First, the slide that controls envelope motion must easily accept the envelope when it is placed on the platen, but must be able to grasp the envelope when it is withdrawn in the sliding motion that opens the flap.  This is accomplished by a pincer mechanism controlled by the knob that is used to operated the slide.  When the knob is pushed to move the envelope forward and end of travel is reached additional pressure on the knob lever will snap it to a forward position which clamps the pincer on the envelope and permits it to be pulled back with the slide.  As end of travel in the home position is reached additional withdrawal pressure on the knob will undo this latch and free the envelope.  The latching mechanism is a cabinet latch operating on the diameter of the rod that supports the knob.  A close-up view of the latch and pincer mechanism is shown in Figure 6.

The layout of the envelope stuffer is highly dependent on the type of envelope being used.  These factors include the flap width which can range from a narrow flap without much taper to the edges to a wide flap that has a large taper to the edges.  These factors affect the location of the rod that flips open the flap and the home position of the envelope with respect to the insert tray.  Consequently, the envelope that will be used should be known when the design is made.

Another factor affecting the design is that envelopes often have windows to show addresses located on the insert.  The edges of these windows are internal to the envelope and the edges of the windows can catch on the envelope opening blades.  This can be mitigated either by altering the blade length (as has been done for the outer or auxiliary blades) or by shaping the blade such that the edge will lift slightly to look like the front end of a ski before reaching the flap.  This bend is noted in Figure 1. This is accomplished by a small bend near the end of the blade where the bend point acts as a pivot to raise the blade end as the far end of the blade is lowered along with the front edge of the insert tray.

New envelopes will normally be quite flat with very little space between envelope front and back at the envelope mouth.  Thus for a blade to penetrate this seam it must be forced against the back of the envelope (which lies on the platen).  This is accomplished by the cam mechanism shown in the accompanying pictures that rotates the rod upon which the blades are mounted.  The center blade is fixed to the rod with a set screw and thus its rotation is controlled by the rod and cam.  In the current mechanization the blade is in the way as the envelope flap is opened.  For this reason the cam must allow the blade to be flipped back by the flap to allow the flap to pass under it.  Design features that permit this to happen can be observed in Figure 3.  The cam design also reduces pressure on the blade tip after entering the envelope to minimize the likelihood that the blade will catch on the edge of an envelope window.

Another feature that facilitates proper operation is the handle that is grasped to raise the  insert tray. Details of this handle are shown in Figure 5. As this handle is raised to lift the insert tray, tines on the opposite side of the handle to clamp the inserts in position so they will not slide toward the mouth of the envelope before the blades have properly opened the mouth area.

A spring is required to hold the insert tray in the upright position.  A suitable spring type is shown in Figure 8.  This spring is attached to the lower side of the platen with an eye screw on one end and the other is attached to a rod spanning the insert tray pivots that moves as the tray pivots.  The same rod is also used in the interlock that prevents collisions of the envelope slide with the blades of the insert tray.  The knob and latch mechanism that moves the envelope slide contains on the under side a pin that is constrained by the ends of a slot milled into the platen to control movement.  The interlock mechanism slips over this pin from the under side such that a slide bar moves on the underside along with the slide on the top side.  When the insert tray is in the up position this bar will abut the rod to which the spring is attached.  Any forward movement of the envelope slide will push the insert tray to the down position, thus avoiding any collision between the slide and the envelope opener blades.  Alternately when the insert tray is in the down position and the slide is forward the lower slide bar passes beneath the spring attachment rod and blocks its movement to the upward position.  Thus in either situation the blades are protected from damage.  Details of the slide bar interlock mechanism are shown in Figure 8

Finally, a board (pointed out in Figure 1) is provided at one end of the base of the stuffer so that it could be clamped to a work surface to prevent sliding around on the work surface when the machine is operated.

A prototype of the stuffer was delivered to Options of Linn County and testing revealed the following issues:

1. When motor functions of the consumer resulted in very jerky motion applied to the slide knob the latching mechanism that grasps the envelope could be set or reset by the inertial force from the jerk applied to the handle.  The best way to overcome this might be to drive the slide movement electrically where only button pushes are required to cause the movement.
2. It was possible to move the slide forward at the same time the insert tray was in the up (insert) position.  This permitted a collision between the slide and the blades on the insert tray which could damage the blades.  This was corrected by providing an interlock that would push the tray down if the slide were moved forward while the tray was up.  The same interlock prevents the tray to be lifted while the slide is in a forward position.
3. When several pieces of material were to be inserted into the envelope the build-up of thickness would sometimes cause the top of the insert pile to hang up at the edges of the envelope mouth.  This was corrected by providing auxiliary blades at the edges of the insert tray in addition to the main blade in the middle of the tray.  A later modification not shown in any of the figures is the addition of stops mounted on the shaft supporting the blades that limit the travel of these auxiliary blades to keep them from flipping 180 degrees and thus becoming useless.  These stops are small cylinders, locked to the shaft by a set screw, that have a tab extending over the blade to limit its travel.
4. Different consumers preferred to operate the stuffer from one side or the other necessitating thumb slots for envelope removal on both sides of the machine.
5. When the slide was pulled back with a very rapid motion the opening flap of the envelope could flip the main (center) blade over leaving it in a useless position.  To correct this a stop that limits blade motion was added.  This stop mechanism is shown in Figure 7.

Items 2, 3, 4 and 5 have been incorporated in the design.  Note that some of the photos used in Figures 1 through 8 were taken either before of after these modifications.

The updated version of the envelope stuffer has been delivered to Options of Linn County.


RCRV designer is Russell Schuchmann, and was requested by Options of Linn County, Wayne Clayton. The project was begun Dec 30, 2008 and completed Mar 30, 2009.


Additional Information:

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Envelope Stuffer Figures

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