PROFILEABLE TRANSMISSION

 

Profileability differentiates the Cyclone Cable Piston from all other linear actuators on the market.

Profileability is the ability to "program" varying reductions throughout the stroke of the actuator. This novel ability to set varying ratios throughout the range of motion allows designers to work with ideally sized motors that would otherwise be oversized.

Conceptually, a profileable Cyclone Cable Piston can be thought of as a high-efficiency screw whose lead can be varied along the length of the screw. The "nut" that would normally travel with constant lead along the screw can be made to speed up, slow down, stop, or even reverse direction while maintaining constant angular velocity of the screw.

These are the three possible benefits of Profiled Rotors:

 

Torque Normalization

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A common drawback to articulated design, also known as linkage design, is that structures are often stressed higher at certain points in its kinematic than in others.

 
 
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Our own musculoskeletal structures suffer from this issue as well: For example, the quadriceps develop increasing tension as one lowers into a squat. Linkages in general, and linearly actuated linkages in particular, are consistently plagued with this issue.  

However, the Cyclone Cable Piston can balance out the increasing tension when properly profiled. By creating a profile that counteracts the effects of geometry and leverage, the motor that drives the Cyclone can run at a constant operating point through the full range of motion. This unique benefit allows one to design with full motor power at their disposal, regardless of the existing kinematics challenges in the linkage space.

Compared to a conventional constant-reduction linear actuator, average power and efficiency are improved by mitigating current losses and increasing average actuation speed. With this methodology, the designer may choose to benefit from added power or from the ability to downsize the motor.

 

EXAMPLE PROFILE of TORQUE NORMALIZATION

 
 
 

This profile was created to normalize motor running conditions for a particular lifting design. The X-axis denotes the motor revolution count, starting from zero which coincides with the contracted state of the actuator. As the motor revolution count increases, the actuator extends, shown in red. As can be seen, the output position increases non-linearly to 165 mm. This is known as the stroke, and is reflected by the actuator's 565 mm extended length and 400 mm contracted length.

The Cyclone lead, shown in orange, carries the same convention as a screw. It is dimensionally defined as [length/ [revolution], and reflects the linear travel of the output per revolution off the screw. After a quick transition through the first three revolutions, the lead reaches a peak at 13 mm/rev. At this instant, the actuator is extending at a rate of 13 mm per revolution of the motor. This value tapers non-linearly down to zero, in order to effectively counteract the effects of geometry and leverage that are evident in the design.

 
 

This profile negates the force profile of the actuator, which is heavily loaded near extension, and lightly loaded near contraction. Note that its behavior is described as "extending from its contracted state" for the purposes of comprehension. In reality, the Cyclone Cable Piston provides positive power during contraction, which is exhibited as the motor revolution count and the output position both decrease from right to left on the above plot.

 

ZERO-CURRENT HOLDING

 

Designers are often confronted with a tradeoff that involves efficiency, backdrivability, and hold currents. High efficiency drivetrains, such as ball-screws, low reduction planetary gearboxes, and harmonic drives offer high power transmission with low frictional losses. The downside to these drivetrains is their inability to hold a position without current from the motor. This often leads to the integration of clutching and braking mechanisms, or the use of locking hydraulic or pneumatic cylinders. 

Low efficiency drivetrains, such as lead-screws and worm drives, with their inherent friction have the capacity to hold the structure at any position, even in the absence of motor torque and current. However, due to the high frictional characteristics of these drivetrains, they are by definition not backdrivable and they are also typically highly inefficient. Thus, a designer is often put in a position where they must either choose backdrivability and efficiency, or zero-current holding, in the absence of additional mechanism design.

 
 

A designer who uses the Cyclone Rotor Profiling can have the best of both worlds. The Cyclone actuator is inherently back-drivable and highly efficient while integrating positions at which the Cyclone lead drops to zero and returns, rendering a unique stable zero-current (and zero-torque) hold positions. Thus, the actuator may be energized and run through its paces, and also have the ability to rest at one or more positions of the designer's choosing.

 

ZERO-CURRENT HOLDING EXAMPLE PROFILE

 
 
 

This plot demonstrates the zero-current holding benefit of the profileability feature. Integrated into a standard lead profile are three positions at which the actuator may rest indefinitely. Note that the output position increases linearly with revolution count, as one would expect from a standard lead "screw" system. However, three humps are observed that coincide with the drops in the lead profile. While in use, the controller may spin the motor into any of those three angular positions and then remove power while the Cyclone holds tension statically. The actuator will remain in this state until the motor is again re-energized and the Cyclone exits the holding state. The Cyclone 3 provides positive power during contraction, which is exhibited as the motor revolution count and the output position both decrease from right to left on the above plot.

 

Two-Stage Transmission

 

A transmission differs from a simple drivetrain in that has the capacity to deliver power through multiple reduction ratios, or through a continuum of reduction ratios in the case of continuously variable transmissions. The benefits of a transmission are enormous, and essentially expand the range of what the system is capable of achieving.

 
 

Our musculoskeletal systems have a "transmission" of sorts, consisting of fast-twitch and slow-twitch muscle fibers. Though not entirely analogous, as they deliver power to our skeletons in parallel as opposed to modifying the properties of a single serial power element, the benefits of both fiber types are clear. Slow-twitch fibers fatigue very slowly if used within their limits, and are capable of repetitive and smooth motionFast-twitch fibers fatigue quickly but provide explosive power, in the circumstances where the slow-twitch action does not suffice. Both are integral to musculoskeletal functionality.

Typically transmissions are quite complex and draw heavily from many resources: design timematerial complexitycomponent countweight, and cost. Such heavy drawbacks are often still outweighed by the huge benefits that transmissions have to offer a designer and the end user. The Cyclone Cable Piston can achieve fast & slow twitch transmission functionality with little more than a profiled two-stage plastic rotor.

TWO-STAGE TRANSMISSION EXAMPLE PROFILE

 
 

Take a look at the zero line in the Cyclone Lead plot for reference. From it's contracted state, the Cyclone Cable Piston extends through 40 revolutions at a constant lead of 4.5 mm. At revolution 40, however, the lead undergoes a rapid transition to -13.5 mm/rev. From this point, as the motor continues to revolve in the same direction, the Cyclone is contracting, and is doing so 3x faster (and weaker) than the initial extension.

Depending on which direction the motor is spun when it approaches the transition range, the actuator may maintain its current reduction ratio or choose to transition into the other. This may also be seen from the perspective of output position. The left-hand, flatter section of the output curve corresponds to the high-reduction regime: Many motor revolutions correspond to the full stroke of 180 mm. The right hand, steeper section of the output curve corresponds to the low-reduction regime: Few motor revolutions correspond to that same stroke range. The Cyclone Cable Piston contracts as it moves away from the peak in the position plot that is evident at 42 motor rotations. One may rotate the motor in either direction and achieve a contractile behavior, though naturally it will reside in one of the two advantage regimes.

 

Please note that these examples are purely demonstrative and do not reflect the limits of the design scope.