22 Jun, 2009 Why do the product teardowns? M3 Design Product Teardown Waterpik WP-100 Oral Irrigator Part of the product development process is to apply knowledge gained from prior experience during the concept development and design phases. Some experience comes from actively designing something in the past while other experience is gleaned from more indirect sources. It is this indirect product development experience that we gain via product teardowns. Teardowns are different from reverse engineering Reverse engineering is nothing more than figuring out the design and manufacturing methods of a product, typically for copying. Conversely, M3 Design views product teardowns as ways to gain insight into the design to become better product developers. We focus on "why" questions. Why did the designer make the choices they did? Why were specific construction techniques chosen? Why were certain features included and others left out? Why was the particular design approach chosen? This serves to gain more in depth understanding into the product's design rather than a superficial once-over. How does M3 Design approach product teardowns? Our teardown process is a rigorous approach to carefully catalog the product s deconstruction in both pictures and written descriptions. This procedure serves two purposes: 1. It forces the deconstruction team to carefully investigate the product pieces and learn as much about the design details as possible. 2. It provides a detailed record of the process for future reference by other designers. The end result of this meticulous process is the beneficial expansion of applicable knowledge regarding product designs. We employ the lessons and insights garnered from these teardowns during brainstorms, design, prototype development, and troubleshooting. This method of obtaining indirect product development experience is just one of many important tools that sets M3 Design apart from other product development firms. M3 Design, Inc. 2009 www.m3design.com page 1 of 14
Overview For this exercise, we chose to focus on a consumer home healthcare device. The Waterpik WP100 is interesting because of the variable force pulsing jet to help clear away food particles. It is also in wide use and is a highvolume consumer product. Once we got into the guts of the product we were impressed by the thought that went into its design. Initial Observations Overall view; different attachments; storage of attachments in the reservoir cover The outside design of the Waterpik is styled to have smooth, curved lines and be pleasing to the eye. Although this device would typically be found in the bathroom away from general view, the aesthetic design allows it to fit in nicely. The included tips store in the reservoir cover away from view and are protected from general handling. The press-in tips secure with a spring loaded detent. An O-ring seal in the handle prevents water leakage. Each tip has a 12-sided polygon-shaped key that prevents it from rotating after being installed. This locks the tip to the handle but the cap of the handle can turn via ratcheting detent. Presumably this is to allow the tip to be repositioned while at the same time resist rotating from contact with the mouth. The detent provides tactile feedback if something moves during use. Putting this feature into the handle rather than in each tip saves part cost and complexity. Finally, there is a momentary-contact shutoff valve in the handle that allows the user to stop water flow by pressing a button. It doesn t latch so we believe its intent is to provide a momentary water flow stop while repositioning the device in the user s mouth. M3 Design, Inc. 2009 www.m3design.com page 2 of 14
Systems The Waterpik can be classified into three main systems: Reservoir Pump/motor Wand/tip. The water flows through each of these and ultimately into the user s mouth. O-rings and other elastomeric seals were used to provide seals between the systems and to prevent water leakage. The O-rings appeared to be inexpensive Buna-N type, adequate for the intended environment. Reservoir The reservoir held up to 600 ml of water and had a plunger type seal on the bottom that prevented water from exiting until it was placed on the main base. A feature on the base pushed up the seal and allowed water to flow Elastomer seal on reservoir (left) and plunger on base (right) Reservoir plunger closed and open M3 Design, Inc. 2009 www.m3design.com page 3 of 14
Initial Observations We found conflicting definitions of duty cycle. The owner s manual states that the device can be used for 5 minutes, followed by a 5 minute cool-down (50% duty cycle). However, the bottom of the case states a 4% duty cycle (5 minutes on, 120 minutes off). We are not sure which is correct, however either should be adequate for the normal, intended use of oral irrigation once or twice a day. 4% duty cycle warning M3 Design, Inc. 2009 www.m3design.com page 4 of 14
We found a simple flapper-type one-way valve that prevents water from flowing back from the wand into the system. It appeared to be stamped from a piece of polymer coated paper, likely a food-grade material. One-way flapper valve where the wand cord attaches. First O-ring found in wand attachment Removing pieces from the cover Unit disrobed M3 Design, Inc. 2009 www.m3design.com page 5 of 14
The case on/off switch was interesting in how it actuated the electrical contact. The rocker on the case rotated an arm in a slot, converting rotary motion to linear. The linear motion moved a round plunger in the electrical housing. An elastomeric seal prevents water entry. At the end of the plunger is a metal clip that closes the contact between the AC hot side and the transformer. Switch assembly. The black elastomeric seal keeps water out of the electrical connections. Switch assembly. Note the rocker arm in the slot and metal clip that completes the electrical circuit. Rocker switch moving the plunger. Although the metal clip inside the plunger isn t visible, it completes the circuit between the AC hot and transformer input. M3 Design, Inc. 2009 www.m3design.com page 6 of 14
We had expected the motor drive to be an inexpensive DC motor and were surprised when we found a single phase synchronous induction motor instead. This motor type does not require magnets to operate, but utilizes an induced magnetic field to cause the motor to spin. Probing the induced motor voltage Motor voltage was 13 VAC Motor assembly. Transformer, stator laminations, and rotor/pinion Close-up of rotor/pinion assembly. Motor stator and transformer removed, showing rotor/pinion and pump Rotor removed showing pump. M3 Design, Inc. 2009 www.m3design.com page 7 of 14
The pump is a simple reciprocating piston design. An eccentric on the driven gear provides the offset that forces the piston in and out of the cylinder. The driving gear was permanently attached to the motor rotor, with 21 teeth. The driven eccentric gear had 56 teeth, for a total reduction of 2.67:1. The entire pump housing plate is connected to the main product body with five elastomeric bushings. This helps isolate vibration coming from the reciprocating pump. On larger products, such as a reciprocating saw, a pump would likely employ a counterbalance mass to reduce vibration amplitude. Clearly that would be overkill for something as small as the Waterpik. Pump gear removed. Note the five elastomeric supports for the pump unit. Detail of pump gear: simple eccentric to drive the pump piston. One very interesting item was another eccentric adjustment on the bottom of the unit. The eccentric adjusts the position of the shaft supporting the pump eccentric gear. This is likely done for one of two purposes. First, the gear tooth clearance between the driving and driven gears can be adjusted. This can impact the noise and backlash in the gear train but since the motor only turns in one direction it doesn t seem necessary to have very low backlash. The other possible reason is to adjust the top dead center (TDC) of the piston travel within the pump cylinder. The total adjustment range is about 2mm. Pump housing plate with gears remove Underside of pump plate showing adjustable eccentric on the driven gear M3 Design, Inc. 2009 www.m3design.com page 8 of 14
The piston uses an elegant flexible skirt as the sealing device and the combo was a single molded part. The skirt was about 0.2mm (.008 ) thick and provides a snug, continuous seal inside the cylinder. As shown in the pictures the skirt flares out slightly. When the piston is moving into the cylinder the pressure of the water causes the skirt to flare out more, providing an even tighter seal. The piston was connected to the connecting rod via ball and socket. Functionally this prevents over-constraint, but molding the ball may be tricky to avoid flash on the curved surface of the ball. Exploded view of piston and connecting rod. Ball and socket to prevent over-constraint. Close-up of piston showing thin sealing skirt M3 Design, Inc. 2009 www.m3design.com page 9 of 14
The pump housing is a complex molded part with multiple pulls in the mold. This part likely makes up a fair portion of the BOM cost. The function is fairly simple: pull water in from the reservoir and force it through the wand tip. In order to do this there is a check valve installed that prevents water from flowing in an undesired direction. Multiple views of pump housing. Note the O-ring seal where the check valve installs. Check valve assembly. M3 Design, Inc. 2009 www.m3design.com page 10 of 14
Water intensity is set by an adjustment knob on the main housing. There are no units and only the water output force changes, not the pulse frequency. At the lowest setting 200 ml of water is consumed in 94 seconds, using the standard tip. At the highest setting, 200 ml of water was consumed in just 34 seconds. Each pulse from the pump was much more forceful at the higher setting as well. As the piston pulls in water from the reservoir, water flows past a check valve and into a lower chamber. The adjustment knob positions a small groove over pump outlet #1 and by turning the knob the resistance to flow changes. When the resistance is low, more water flows back into the main chamber and less flows out to the handheld nozzle. When the resistance is high, less water flows back into the main chamber and more flows out to the handheld nozzle. Presumably, this is so the pump and motor see a relatively constant load no matter how much water flows to the handheld nozzle. Flow in from reservoir Check valve Adjustment Knob Assembly Pump outlet #1 Piston Pump outlet #2 M3 Design, Inc. 2009 www.m3design.com page 11 of 14
Wand Assembly The wand handle is a two piece shell that is glued together. Inside were the momentary shutoff valve and connection for the tip. The momentary shutoff uses a piston with two O-rings to block the flow of water from reaching the tip. While this used more parts it probably saves wear and tear on the tube that would occur if a pinch valve was used. The tube is secured to the wand valve housing with a classical barb and sleeve connection. Wand dismantled Momentary shutoff valve components The tips are held in place with a simple lock tooth that fits into an annular groove in the tip. The ratcheting cover is spring loaded so that when the lock is depressed the tip is ejected. This visual feedback also lets the user know if the tip is secured after installation. Tip before installation Nearly secured. Note the ratcheting knob is extended M3 Design, Inc. 2009 www.m3design.com page 12 of 14
Tip is secured and ratcheting knob is locked in place. Ratcheting knob removed showing internal ratchet teeth and tip ejecting spring Locking mechanism O-ring seal for the interchangeable tips Barb connection with compression fitting to secure the tube M3 Design, Inc. 2009 www.m3design.com page 13 of 14
Conclusions The Waterpik is deceptively simple in construction, yet offers sophistication in its detailed design. Some design details are clearly intended to reduce costs, while others seem to only increase product cost without an obvious benefit. Perhaps it is possible that these features are common to multiple product versions and just not used in this one. This would permit common parts usage across multiple products which can reduce development and tooling costs overall. As with any product there are constraints to be met and ultimately a cost/feature balance must be made. M3 Design, Inc. 2009 www.m3design.com page 14 of 14