M3 Design Product Teardown Ameda Purely Yours Breast Pump

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1 28 Sep, 2010 Why do the product teardowns? M3 Design Product Teardown Ameda Purely Yours Breast Pump 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 page 1 of 13

2 Overview M3 has recently been researching small form factor pumps and had the opportunity to take apart a consumer-level pumping product. The patient for this product teardown session was an Ameda Purely Yours breast pump. The team figured, How complex can this product be? As it turns out, the mechanics are simple but the controlling electronics are a bit more intricate than expected. External Construction The outer housing consists of two molded shells held together with 12 small snap fit fingers. The upper shell overhangs a lip in the lower shell, creating a labyrinth seal. This type of interlocking seal is probably a good idea since the product is used around liquids and this design makes the housing more impermeable to liquids. The lower shell has a thick piece of molded mastic installed likely included to damp vibrations and to keep the operating noise low. Overall product view M3 Design, Inc page 2 of 13

3 Noise-absorbing mastic Systems The breast pump consists of three primary subsystems: the user interface, the mechanical pump, and the controlling electronics. User interface The user has two adjustment knobs accessible during normal operation: suction strength and pumping speed. The suction strength knob basically controls how deep the vacuum is drawn. The pumping speed knob controls the dwell time between cycles rather than the actual speed of each cycle. One may guess that these knobs are connected to potentiometers that are read by the pump controller. Once the cover was removed, the teardown team discovered that the detecting circuit is two concentric copper rings and a pair of wiper fingers for each knob. This 2-ring/2-finger setup makes up half of the controlling circuit for both vacuum and speed. The other half will be discussed later. M3 Design, Inc page 3 of 13

4 Concentric rings for knob position inner and outer ring contact points discrete sections on outer ring concentric contact rings Underside of knob showing 2 contact fingers Close-up of concentric contact rings Mechanical pump The pump mechanism is a reciprocating piston with a rolling diaphragm employed as the seal. Part of the diaphragm covers a vent hole in the piston head. When the piston draws back to create suction the negative pressure in the chamber seals the diaphragm over the valve hole. When the piston moves in the opposite direction (compresses the air in the chamber) the positive air pressure unseats the flexible diaphragm membrane from the valve hole, therefore venting the chamber s air to the atmosphere. M3 Design, Inc page 4 of 13

5 piston housing piston head rolling diaphragm piston rear section noise damper plastic lead screw Exploded mechanical pump assembly Rear end of piston head indicating valve seat Front face of piston head showing valve hole M3 Design, Inc page 5 of 13

6 piston head rolling diaphragm piston rear section Piston head and rear piston section are permanently joined in the assembly to capture the rolling diaphragm piston housing flexible rolling diaphragm sealed against valve hole due to negative pressure rolling diaphragm vacuum draw piston back piston head piston rear section Sealed valve during suction stroke of piston M3 Design, Inc page 6 of 13

7 piston housing pressurized air escapes past diaphragm through valve hole rolling diaphragm positive pressure push piston shut piston head piston rear section Open valve hole allows air to escape during compression stroke of piston A simple DC motor (Mabuchi RS-380SH) with an O-ring gear reduction (3.9:1) turns a molded lead screw. The lead screw drives the piston to varying stroke lengths. If anything causes the piston to jam during operation, the team surmised that the O-ring would provide a reliable slip clutch. This feature is critical to prevent the motor from burning up. We found that the fixed end of the lead screw is housed in a shielded ball bearing (607Z). While a less expensive, molded plastic PV bearing could have been used, the advantages of a ball bearing such as lower noise generation, better handling of high rotational speeds, and prolonged operating life may warrant this more expensive component. The floating end of the lead screw is supported by the internal threads of the rear piston section. Initially perplexing was how the device regulated how far to draw back the piston based on the useradjusted suction strength setting more on that later. M3 Design, Inc page 7 of 13

8 Pump, motor, and lead screw End view showing lead screw bearing M3 Design, Inc page 8 of 13

9 Controlling electronics While the mechanical pump was fairly straightforward, the electronics were a bit more elaborate. The major components consist of the microcontroller, motor control, and piston position feedback. The microcontroller is a Zilog Z86E0412SSC 18-pin device, which controls all aspects of the product. The motor control is handled by the microcontroller, which activates and deactivates a pair of N- and P-channel MOSFETs, forming an H-bridge. This configuration allows bi-directional control of the motor. Because an H-bridge also allows speed control of a motor, it may be implemented in this product to keep the motor at maximum efficiency. The motor speed did not vary during operation, however. The final electronics feature we investigated was the piston control feedback. There are two linear copper traces on the bottom of the PCBA which served an integral part in position control. A wiper assembly attached to the piston contacts these traces forming part of a circuit. The Suction knob concentric traces (see User Interface) completes the circuit. The combination of the knob position and the piston position sends a signal from the knob through the linear wiper to a multiplexer (MUX). The MUX reads which channel is ON and sends a 3-bit output signal to the microcontroller. Based on the 3-bit signal the microcontroller changes the motor s direction to reverse the piston. This system is how the product controls the suction strength level. M3 Design, Inc page 9 of 13

10 Linear traces on control board and associated piston wiper fingers M3 Design, Inc page 10 of 13

11 Simulating piston position feedback Summary & Conclusions Initially, the team was a bit surprised about the complexity of the electronics control incorporated in this product. At first glance it seems overkill. However, the need to reliably sense piston location probably necessitates the subsystem electronics we discovered. The $160 retail price of the product certainly supports the development and manufacturing of a complex PCBA. The mechanical components also seem to be high quality. The molded parts are nicely made and everything has a precise fit without any undue sloppiness between components. Epoxy or hot melt glue is used in a few places to ensure any clearances between parts are filled. Using glue as a gap filler tends to be an oops -type afterthought, but no design is perfect. Reflecting on this system s design, it appears the copper trace wiper is a simple way to provide reliable piston and knob feedback for the entire life of the product. While the two user input knobs could be connected to potentiometers, it would require the microcontroller to have two analog inputs to read the knob position. In all likelihood, a linear potentiometer for detecting piston position would not support the required product life and would also increase the friction force the motor must overcome. Since the product can be powered by AA batteries or an AC adapter, it is logical to reduce the load on the motor to improve battery life. M3 Design, Inc page 11 of 13

12 Example of clearance-reducing glue Motor and controller; microcontroller is visible on the right side of the board M3 Design, Inc page 12 of 13

13 Electronics chips HEF4051BT 8-channel analogue multiplexer/de-multiplexer, used as a digital MUX/DEMUX. In this product it was used to determine how far the piston should travel based on the user control knob setting. Depending on which of the input channels was connected, the 3-bit output value changed, therefore telling the micro-controller where the piston was positioned. Zilog Z86E0412SSC microcontroller 18 pin MCU, 14 I/O lines, 2 analog comparators. International Rectifier IRF7105 HEXFET power MOSFET (2 ea) Dual N and P channel MOSFET; set up as an H- bridge to control motor direction. M3 Design, Inc page 13 of 13