Linkages
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Examples below on controlling machine functions, low-cost, high-speed feeders, & ultra-low cost solar mirror drives.

In addition to his expertise showing companies how to design machinery for manufacturability, Dr. Anderson is also an expert in designing linkages to generate motion functions for low-cost control of repetitive functions.   To illustrate the many functions that can be generated by linkages, he created the following model that plots out many functions from the illustrated linkages:

Motion Control with Linkages


Linkages provide a low-cost way to control repetitive machines. They can be driven by any shaft rotating at one revolution per cycle. Many repetitive machines have one of these shafts somewhere. Controlling machines with linkages will ensure the:

Lowest Possible Cost. Linkages consist of a crank mounted on an input shaft, driving a coupler link (usually a tube with rod end pivots on each end) that drives an output crank. This will cost less than cams and a lot less than computer controlled servo mechanisms or robots, either of which would be an overly expensive overkill to .control simple repetitive motions.

Cleanest possible mechanism. Linkages are clean, open, run without lubricants, and will not contaminate products or be affected by dirty environments. They do not have to be enclosed to keep lubricants on cams or keep liquids out off or electronic controllers and associated power and signal cables.
      This cleanliness makes linkage controls perfect for food processing, pharmaceuticals, and for semiconductor fab clean rooms. In fact, Dr. Anderson has designed ultra-clean wafer handling mechanisms that use non-pivoting flexing bearings near semiconductor wafers. He has also designed linkage-driven food processing to satisfy FDA cleanliness requirements.  This replaced an painted machine that was  lubricated with oil and grease with an all stainless-steel machine that was open enough to hose down and fully inspect.  It even had nozzles mounted on its pressurize frame!

Easy to build. Linkages are very easy to fabricate and assemble by low-skilled labor. First of all, the input shaft may already be in the product architecture as a gearmotor shaft or a gearbox shaft, or a two-shaft gearbox would be expanded to three or four.
     The input crank can be made from bar stock and be bolted to an off-the-shelf shaft collar. The coupler link would most likely be an internally threaded tube with off-the-shelf rod-ends or ball joints threaded and locked to each end. The output crank may just be an arm rotating protruding from the controlled member or the output crank would actually be the controlled member, which would be guided and supported by the linkage (next point).

Motion guidance. Linkages can guide and support parts or grippers through 3-dimensional space. This would obviously be less expensive and easier to build than separate systems for to (1) support the load on the moving member and (2) control the motion, with more expensive cams or computer controlled actuators.
 

Example # 1: Complex food processing machine controlled entirely by linkages. In order to satisfy increasing FDA pressures for food processing cleanliness, Dr. Anderson designed linkage-driven machine that removed the pits from peaches, which was known as the “Clean Pitter.” The drawing at the right, from Patent # 4,380,953, shows the various linkages that would: orient the peach, grip it, transfer it into a pair of blades, close the blade to grip the pit, and rotate rubber grippers in opposite directions thus cutting the peach in half – at 90 per minute.. Since this was a redesigns for cost, speed, and cleanliness, it preserved the “crown jewels” of peach pitting that was refined over decades, whose motions were guided by greased steel and controlled by a “geneva” (indexing) mechanism in an oil bath over the food zone. This effective process is known as commercialization that Dr. Anderson also teaches.  See: http://www.halfcostproducts.com/commercialization.htm  .
       The result was a low-cost, all stainless steel machine that could easily be cleaned with its own nozzles tapped into its pressurized frame! Since the linkage mechanisms were lighter and stronger, the machine ran 50% faster.
      To see a PDF brochure of the current version, click on the "Clean Pitter II," link at the lower right of: http://www.atlaspacific.com/#!peach-pitter/c6ic .  (Historical footnote: Dr. Anderson worked his way through college as a cannery mechanic working on Atlas Pacific food processing machines.)

Example # 2: Quick-return constant-speed feeder
. Dr. Anderson designed an inexpensive 6-bar feeding linkage to drive a pusher to feed a scented pad into a “stick up” product. In order to align the pad with the base part (which was moving along a conveyor belt), the linkage had to push the pad at a constant velocity, as shown in the velocity profile below. The linkage also had to return quickly to get ready for the next stroke.
        Like most machine control linkages, the input is a one revolution/cycle input shaft, which, in this case, was in sync with the conveyor speed.  The top graphic shows a kinematic layout of the 6-bar linkage pushing the symbol for a sliding member.  The photograph shows the scale mock-up linkage a hand crank as the input and a simulated conveyor pockets.

Example # 3:  Linkage coupling of mirrors for ultra-low-cost CSP mirror guidance.  Conventional Concentrated Solar Power (CSP) power plants use up to 350,000 “heliostat” mirrors that reflect sunlight onto a tower-mounted target.  Currently, each of these mirrors has two motors, two gearboxes, two sets of sensors, and a computer to constantly correct both axes all day.   So a large solar field will have up to 700,000 of these control systems!

          Dr. Anderson has proven that an ultra-low-cost linkage system can couple arrays of heliostat mirrors with low-cost linkages. This has not been done before because no one has yet figured out how mechanically couple heliostat mirrors, since each mirror must go through its unique daily path to reflect sunlight to a stationary tower throughout each day. The field would thus consist of low-cost mass-produced mirror assemblies which would be driven and controlled by one or more central driver(s).  The figure below shows mirrors that individually reflect sun light at the target by coupling them together with inexpensive mechanisms.

Further, focusing sunlight on the tower can be improved 25 times!

Flat mirrors reflect un-focused light. Heliostat mirrors aim their center at the tower, but if the mirror is flat, only the center is focused at the target, and the rest of the sunlight shines above, below, and to the sides of the target. This is because sunlight rays are parallel and flat mirrors will reflect parallel sunlight rays.

Focused mirror facets can be 25 times better focused. On the other hand, sunlight focus can be improved 25 times if the heliostat consists of, say, 25 facets, each continually aimed at the target. In the above illustration, the center mirror has all 25 facets individually aimed at the target  throughout the day, compared to the adjacent mirrors, which are flat for a visual comparison.
       This has been proposed for solar furnaces to replace two-stage mirrors (a tracking heliostat aimed at a large fixed parabola) with a single focusing heliostat focused directly on the ultimate target. However, conventional thinking requires an extra 8 to 24 drives per heliostat. And this can not be retrofitted to current heliostat designs that have an elevation axis mounted over an azimuth (compass direction) axis, which rotates the mirrors out of the tangential plan (formed by the sun, mirror center, and target) in which the needed correction must occur.   So highly focused mirrors need an optimal joint ordering, which is the first step in robot design.
       Fortunately, Dr. Anderson can also apply his linkage expertise to continually focus 24 “slave” mirrors on the target throughout the day.
       This will be especially valuable for (a) generating the most heat and highest temperature for industrial processing or heating large buildings and (b) smaller, more compact mirror fields, where focus is even more important. For Concentrated Solar Power, better focus can allow heliostats to closer to the tower and more concentrated sunlight needs fewer heliostats, thus resulting in more compact fields that neediless land with less permitting challenges

See how this fits into the big picture in the new white paper: "Half Cost Concentrated Power" at: http://www.halfcostproducts.com/half_cost_solar.html

 

Example # 4: Elevating wheelchair. For Dr. Anderson’s thesis project, he designed and built a wheelchair in which linkages guide and support a quadriplegic in many positions for better comfort and to improve indoor mobility and driving.  In the illustration at the right, from patent # 3,882,949. Figure 1 shows the powered wheelchair in the typical position.
     In Figure 2, the long ball-screw actuator (behind the back rest) elevates the seat, while pulling in the feet and narrowing the wheelbase to be able to access high kitchen cabinets without needing leg clearance below, which is a common problem with all other wheelchairs.
     Figure 3, the seat lowers and legs extend to the “go-cart” position for stable running on slopes and for driving in a sedan with low ceilings.   Dr. Anderson also designed and built a scale model of the concept for a linkage-based loading mechanism which would lift the wheelchair, in the low position, and pace it in either driver or passenger seat of a large sedan. In the low position, the back rest can recline to redistribute body weight to relieve and protect the skin.

    The photograph below shows the first six prototypes at a range of seat heights from the fully reclined low position to the highest position (corresponding to Figure 2) with the foot rest pulled in to enable reaching above kitchen counters. As the seat raised, the wheelchair width narrowed four inches for improved indoor maneuverability. 

 

Dr. Anderson can show companies how to incorporate these techniques into their products with seminars and workshops or do design studies working with company engineers to finish the implementation.
 

These are the general principles. Pass around this article or URL to educate and stimulate interest

In customized seminars and webinars, these principles are presented in the context of your company amongst designers implementers, and managers, who can all discuss feasibility and, at least, explore possible implementation steps

In customized workshops, brainstorming sessions apply these methodologies to your most relevant products, operations, and supply chains.

 

Call or email about how these principles can apply to your company:

  Dr. David M. Anderson, P.E., CMC
fellow, American Society of Mechanical Engineers
www.design4manufacturability.com
phone: 1-805-924-0100
fax: 1-805-924-0200
e-mail:
anderson@build-to-order-consulting.com

copyright © 2017 by David M. Anderson

Book-length web-site on Half Cost Products: www.HalfCostProducts.com

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