Patent Grant
7677540
This invention relates to mechanisms that convert the force or torque from a spring into a constant force or torque.
In the mid 1400's, conical shaped spiral pulleys called fusees were first used to improve the accuracy of spring-powered clocks. The fusee converted the linearly increasing torque from a power spring into a constant torque.
The fusee fell out of favor after the invention of constant force and constant torque springs. The constant torque power springs were no larger than the linear power springs that they replaced. The fusee clocks were larger and they had more moving parts. Constant force and constant torque springs haven't replaced spiral pulleys for all applications. They store less energy per pound and they have a shorter life than other springs. Their force fluctuates slightly as they extend and retract. It's difficult to produce constant force springs with a tight force tolerance. They are not adjustable. In the United States, only a few dozen sizes of constant force springs are available from stock. Other sizes must be custom made.
In addition to the extra parts and space required, spiral pulleys and fusees have other problems. The cables can rub and wear on the sides of the grooves in the fusee. Rubbing occurs when the cable is not tangent to the groove. For example, if the cable approaches the fusee from a nearby idler pulley, the angle between the cable and the groove can be large. This angular error is often called the “fleet angle”. U.S. Pat. No. 5,037,059 discusses one specific solution to this problem.
Spiral pulleys and fusees are poorly understood and difficult to design. The shape and size of a spiral pulley is affected by many parameters. Most patents give only a limited description of their geometry. For example, the 059 patent describes the fusee as “corn shaped”. U.S. Pat. No. 4,685,648 describes the spiral pulley as “irregular” or “snail-shaped”.
FIG. 7 of the 648 patent shows a constant force mechanism with two spiral pulleys. Both the input and the output pulleys are spiral shaped. In other patents and references, only one of the two pulleys has a spiral shape. In FIG. 5, only the input pulley is a spiral. In FIG. 6, only the output pulley is a spiral. The 648 patent does not explain how to determine the shapes that will produce a constant output force.
In
In
It is an object of this invention to provide a pulley mechanism for converting the force from a linear spring into a constant force. The pulley mechanism should be significantly smaller than previous constant force pulleys.
It is a further object that the mechanism should be accurate and have low friction. If required, the mechanism should be adjustable so that a desired force can be reached even with commercial spring tolerances.
For general-purpose use, a limited number of pulley sizes should cover a wide range of applications. The required output force and travel may vary over a wide range. The orientation of the spring relative to the output cable may vary. The pulley mechanism should work with thousands of readily available helical extension springs. The pulleys should be easy to apply and use. Cable friction and wear caused by a nonzero fleet angle should be reduced or eliminated.
The constant force mechanism has an input pulley 1 and an output pulley 2. Each pulley has one flat face. The flat face of one pulley rests against the face of the other. An 18 tooth internally splined hole 3 passes perpendicularly through input pulley 1. A 20 tooth internally splined hole 4 passes perpendicularly through output pulley 2.
The input pulley is attached to the output pulley with a differential spline hub 5. The hub is cylindrical. It has a round bore through its center and one external annular groove at each end. An 18 tooth external spline is located just inside the groove at one end of the hub. A 20 tooth external spline is located just inside the groove at the other end of the hub. The 18 tooth end of the hub 5 engages the splined hole in the input pulley 1, and the 20 tooth end of the hub engages the splined hole in the output pulley 2. The 18 tooth and 20 tooth combination provides for a total of 180 evenly spaced orientations of the two pulleys.
The assembly is held together with a retaining ring 6 in each hub groove. For low friction, a needle bearing 7 is pressed into the bore in the hub 5. When cost is more important than friction, the needle bearing can be eliminated, and the hub can act as a bearing. The dual pulley assembly rotates about a shaft 8 that passes through the bearing.
Both pulleys are non-circular. Each pulley has a v-groove 15 around its periphery. The shape or profile of the pulleys will be covered later. Input cable 9 rides in the v-groove of the input pulley 1. Output cable 10 rides in the v-groove of the output pulley 2. The force in the output cable is constant over the working range of the mechanism. A cable termination 11 is crimped onto one end of each cable. Each cable termination is captured in a slot 16 in the face of its pulley.
One end of a helical extension spring 12 is fixed to ground. An adjustable end plug 13 is screwed into the spring coils at the opposite or free end of the spring. A cable tension adjusting screw 14 is screwed into a threaded hole 20 in the center of the adjustable end plug. The adjusting screw has an axial hole 36 through its center. The free end of the input cable 9 passes through the hole in the adjusting screw. Another cable termination (not shown) is crimped onto the free end of the input cable.
Looking at
Dual Pulley with Radial Grooves
The radial groove design has several advantages. The hub is smaller in diameter than the differential spline hub. Smaller pulleys can be made with this construction. There are more grooves and they engage each other at a greater radius compared to the differential spline hub. The load carrying capability should be improved. The radial groove design does not have as fine an angular resolution as the differential spline hub.
Dual Helical Pulley
The path of the v-groove is not a true helix. The axial advance of the groove is not constant with the rotation of the pulley. The groove advances axially at a rate that keeps the tangent to the groove aimed at a remote focal point 35. Figure 11 shows how the tangent lines 33 and 34 intersect at the focal point. The radial profile of the pulley v-grooves will be covered next.
Pulley Profile
Introduction
The pulley shape or profile is a complex subject. The pulley profile depends on several variables. For a given spring, output force, and travel, there are an infinite number of profiles. Some profiles are more useful than others are. One objective of the preferred embodiment is to minimize the size of the pulleys.
The preferred pulley profile is a composite of shapes. The output pulley has a constant radius portion, a sinusoidal radius portion, and a linear radius portion. The input pulley has a constant radius portion. It also has a portion where the radius is determined by a sinusoidal portion of its torque profile and it has a portion where its radius is determined by a linear portion of its torque profile.
A better way to visualize pulley geometry is to look at a Cartesian graph of pulley radius as a function of angle.
There are three different types of radii. This can be confusing. The true radius is the distance from the pulley axis of rotation to a point on the pulley. The tangent radius is the normal distance from the axis of rotation to a line that's tangent to the pulley. The radius of curvature has its common definition. All three radii are important. The size of the pulley depends on the true radius. For example, the spiral pulley in
There are two important angles. The pulley angle measures the pulley orientation relative to ground. The cable wrap angle measures the cable orientation relative to the pulley. The two angles are not the same because the orientation of the cable relative to ground changes as the pulley radius changes. The pulley shape is a function of the cable wrap angle. A graph of the pulley radius as a function of the pulley angle does not fully define the pulley shape.
It will be shown that it's useful to specify pulleys by their torque profile, not their shape. Input pulleys have a different shape than output pulleys. The pulley shape depends on other variables. The constant force mechanism will work properly only if the torque profile for the input pulley is symmetric to the torque profile for the output pulley.
Pulley Radius Limitations
Not all of the spring energy can be converted to a constant output force. In
In
Derivation of the Pulley Transfer Function
F=KL Eq. 1
Length Lmax is the theoretical distance, starting from zero force, required to reach a maximum force, Fmax. E, is the energy required to extend a theoretical spring starting at a force of zero at zero extension, up to the maximum force Fmax. This energy is equal to the total area under the curve.
E=½LmaxFmax
The fraction x, is a number between zero and one. The constant force pulley mechanism operates between a force xFmax and Fmax. At the force xFmax, the spring is extended by a length x Lmax. The distance L1 is the operating spring extension between force xFmax and Fmax.
Lmax=xLmax+L1
or
Lmax=L1/(1−x)
Etran, is the energy transferred by the constant force pulleys when the spring is extended over its operating range, between x Lmax and Lmax.
Etran=Fmax(1+x)L1/2 Eq. 2
Fout is the constant output force from the mechanism and L2 is the output cable travel that corresponds to the operating spring extension L1. If we assume that the pulley mechanism is frictionless, then by conservation of energy:
Etran=FoutL2 Eq. 3
Solving for Fout:
Fout=Fmax(1+x)L1/(2L2)
The spring constant K can be calculated as follows:
K=(Fmax−xFmax)/L1
Solving for Fmax, and substituting into the previous equation yields:
Equation 4 can be converted to the following form:
Note that equations 4 and 5 do not depend on the shape of the pulleys. The equations hold for all six constant force mechanisms in
Derivation of the Pulley Profile
f0=xFmax.
The cable travel is s, starting with s=0, and F=f0 at λ=0. The spring extension L1 is defined above. L1 is also equal to the total cable travel as the pulley rotates from λ=0 to λmax. We can call L1 the length of the input pulley.
L1=s at λmax
The following parameters fully determine the shape of each pulley.
m=The center distance between points Q and R.
λmax=The maximum angle of pulley rotation.
F(s)=The cable force on the pulley. F is a function of s.
τ(λ)=The torque applied by the mating pulley. τ is a function of λ.
For the input pulley cable, the force is equal to the spring force:
F(s)=Ks+xFmax=Ks+f0 Eq. 6
The torque τ on the input pulley produced by F is:
When the pulley rotates by an angle dλ, the resulting spring extension will be:
d=rdλ
This can be converted into a finite difference equation.
sn−sn-1=rn-1Δλ
sn=rn-1Δλ+sn-1 Eq. 9
Now converting equation 8 into a finite difference equation:
As seen in
ω=λnφn−φ0
Looking at angle φ: φ=sin−1(r/m)
Thus: ωn=λn+sin−1(rn/m)−sin−1(r0/m) Eq. 11
The initial Conditions are:
If we know the constants K, f0, and m, and if we know the pulley torque profile τ(λ), then the pulley tangent radius r can be calculated as follows. Starting with the initial conditions above, using a small step size Δλ, the shape of the pulley can be solved numerically using equations 9, 10, and 11. The tangent radius as a function of the wrap angle gives us the pulley shape.
When the cable is constrained to pass through the perpendicular axis at point R, then the free body diagram in
F(s)=Fout=f0
Prior Art Pulley Shape
a, b, and c show examples of the prior art. In
In
τa=Foutrout
The equation for the torque between the pulleys in
τb=(Ks+XFmax)rin
The output force Fout and stroke L2 are determined by application requirements. If we make assumptions about any two of the three variables L1, x, and K, we can solve for the third variable using equation 5. The center distance m can be selected to suit the geometric constraints of the application. We now have enough information to determine the shape of the pulleys for the prior art mechanisms in
Minimizing the Size of the Dual Pulley Mechanism
Many parameters affect the size of the dual pulley mechanism. These include the input pulley length L1, the output pulley length L2, the output force F, the spring constant K, the fraction of unused spring extension x, and the torque profile τ(λ) and λmax. The center distances m1 and m2 affect the shape of the pulleys, but they have relatively little affect on the maximum size.
To make the problem easier, we can assume that several parameters are fixed. We can assume that we have a given task that requires a force Fout over an extension L2. We can also assume a value for x. All of the pulley mechanisms have similar problems if we try to make x too small. Finally, we can assume that L1=L2.
The last assumption isn't always valid, but it's useful for the following reason. Mathematically, it's always possible to decrease the size of the input pulley L1, by using a spring with a higher stiffness K. The higher stiffness and smaller input pulley will increase the load on the input cable. When L1=L2, the maximum cable force Fin is limited to Fin<2Fout. When the size of the input pulley is reduced by decreasing L1, the input cable force Fin can grow much larger than 2Fout. Setting L1 equal to L2 puts a limit on the maximum cable load.
Pulley Torque Profile
a, b, c and 3a, b, c show six different constant force mechanisms. Each mechanism has been designed to deliver the same output force and stroke. For comparison, all figures have been drawn to the same scale.
The torque is a constant for the mechanisms in
The mechanism in
Limit on the Maximum Angle of Rotation
For a flat pulley in which the groove lies in a plane, there is a limit on the angle of rotation.
In
The Composite Profile Pulley
b is a graph of several composite torque curves. The bottom torque curve is shown with a heavy line.
Only one of the input pulley curves has a constant radius segment. The input pulley will have a constant radius only if the torque curve is linear, and the slope and intercept of the line are properly matched. A torque curve that corresponds to a constant pulley radius can be found in the following way. Select a value for the desired torque at a zero pulley angle. This is the intercept. Then take a guess at the slope of the torque versus pulley angle line, and numerically solve for the pulley shape. If the radius is not constant, modify the slope and recalculate the pulley shape. This process can be used to iteratively solve for the slope of the torque curve that yields a constant pulley radius.
a and 20b are graphs for an input pulley. The graph in
The area under each of the torque curves in
a and 21b are graphs for an output pulley. Output pulley torque curves are shown in
a shows radius curves for the output pulley. These curves correspond to the torque curves in
With equal energy torque curves, when the maximum diameter of the input pulley decreases, the maximum diameter of the output pulley increases. As a result, the size of this dual pulley mechanism will be minimized when both the input pulley and the output pulley have the same constant diameter. This occurs approximately when λb≅133° for the input pulley torque profile. Remember that we have also assumed that L1=L2.
If we relax the earlier assumption that L1=L2, then the size of the dual pulley can be reduced further. Decreasing λb for the input pulley, decreases the diameter of the output pulley and increases the diameter of the input pulley. But if we let L1<L2, then the input pulley diameter can be reduced too. Solving iteratively with smaller values of λb we find that the maximum allowable pulley angle λmax increases to λmax≅302° at λb≅80°. At values of λb below 80°, the maximum allowable pulley angle λmax starts to decrease again. Eventually, the decreasing λmax will offset the effect of decreasing λb and the pulley diameter will start getting larger again.
c shows the input and output pulleys with a composite torque profile and λb≅80°. The mechanism in
In the limit, by decreasing λb to zero, λmax decreases to a little over 130°, just as in
The mechanism in
Transition Between Segments of the Composite Torque Profile
An assumption was made in the previous section. The composite torque profiles are shown with sharp transitions between the linear and the constant segments. The torque profile can't make a sharp transition.
When a constant radius portion of a pulley makes a sharp transition to a decreasing radius, the torque profile follows a sinusoidal curve. Assuming a constant radius r and cable force F, the torque profile follows equation 12.
τ=Fr sin(λ) Eq. 12
In other words, even if the radius drops sharply from r to a smaller radius, the torque is a function of the radius to the tangent, which is r sin(λ).
When the torque profile has the sharpest sinusoidal transition between its segments, the pulley has a sharp corner. This is usually unacceptable.
The radius of curvature of the sharp corner is zero. This will overstress and rapidly fatigue a cable. The sharp corner in the pulley profile can be rounded off in a variety of ways. Arbitrarily rounding the corners of both pulleys will produce errors in the output force. The desired output force can be maintained by further rounding the torque profile and then calculating the input and output pulley profiles from the new torque profile.
A simple way to round the torque profile is to use a sinusoidal transition with a smaller magnitude than before. Equation 13 describes a new transition portion for the torque curve. τconst is the constant portion of the torque profile and τlinear is the linear portion of the torque profile. The new transition portion covers a full 90° of pulley rotation, from λ=λ1, to λ=(λ1+90°).
τtran=(Fr−S)+S sin(λ−λ1) Eq. 13
Where
A graph of equation 13 is shown in
Other Pulley Profiles
There are infinite pulley shapes that will produce a constant output force. Factors other than minimum size may be more important for some applications. For example, the life and strength of the cable is affected by the minimum bend radius of the pulleys. Alternatively, for another application, the sensitivity to cable angular alignment may be more important.
Note that the parabolic profile dual pulley mechanism is about 11% larger than the equivalent composite profile mechanism in
The Affect of the Center Distance on the Pulley Profile
The center distances m1 and m2 affect the shape of the pulleys. This occurs because the center distance affects the cable wrap angle. When the center distance is large, the pulley angle is the same as the cable wrap angle. The difference between the two angles increases when the center distance gets small.
Standardization of the Pulleys
Input and output pulleys with symmetric torque profiles over a given range of pulley angle will produce a constant output force. The pulleys will behave according to equation 5.
Two input pulleys may have identical torque profiles but different shapes. Both the center distance m1 and the fraction x affect the shape of the input pulley. Center distance m1 and the fraction x have no affect on the shape of the output pulley. Two output pulleys may have identical torque profiles but different shapes. The center distance m2 affects the shape of the output pulley, but not the shape of the input pulley.
A series of sizes of input and output pulleys can be designed with symmetric torque profiles. The same value of x can be used for all input pulleys in the series. With x=0.3 the size of the pulleys is reasonable and most of the spring energy storage capacity is used. Each input pulley size L1 can have a standard center distance m1. Each output pulley size L2 can have a standard center distance m2. A good choice for the standard center distance will allow a pulley to be used over a wide range with little error. For example, assume that an output pulley with L2=160 mm (6.30 inches) has a design center distance of m2=12 inches. Looking at
Pulley Alignment and Coupling
To function properly, the pulleys must be aligned relative to each other. Input and output pulleys must be connected by a torsionally rigid coupling. The profile of each pulley is generated relative to a line through point Q and point R as shown in
For general purpose use, the ability to adjust θ is desirable. This allows the spring and cable to be located where they fit best for any application. There are many ways to connect and align the pulleys. As mentioned earlier, the preferred method with the differential spline hub is shown in
Adjustable Force End Plug
The output force from the dual pulley mechanism can be adjusted by changing the spring constant. Equation 4 shows that the output force Fout is proportional to the spring constant K. Unfortunately, it's difficult to manufacture springs with a close tolerance on K. The tolerance on K for helical extension springs is typically no better than ±5. %.
The compliance of a helical extension spring is proportional to the number of active coils. The spring constant K is equal to the reciprocal of its compliance. The number of active coils N can be adjusted by screwing the end plug into or out of the spring. This enables the plug to make a very fine adjustment of the output force. A tight tolerance on the spring constant is not needed.
The end plug has other benefits. It's significantly shorter than the usual end hooks. To save space, an end plug can be used at both ends of the spring. If properly designed, the end plug can reduce the maximum stress in the spring. The highest stress in an extension spring is usually located in the end hooks. With the lower stress, the spring will have a longer life. A plug mounted in the fixed end of the spring can be rigidly fixed to ground. For some applications, an internal thread geometry may fit better than the plug's external thread.
The thread pitch is not constant. The pitch starts at a low rate and it increases parabolicly over the single turn. The parabolic pitch is the same on both faces of the single thread. This results in a thread that is thin at both ends and thick in the middle. The spring coil that contacts the outside face of the thread follows the same parabolic pitch. As a result, the load from the coil is evenly distributed over the single turn. This eliminates the bending loads and stress produced by spring end hooks.
Helical Pulleys or Fusees
As shown earlier, when the pulley groove is constrained to a plane, the pulley rotation is limited to λmax. The rotation limit can be avoided if the pulley groove advances axially as the pulley rotates.
A helix is commonly defined as a curve that lies on the surface of a cylinder or cone and cuts the element at a constant angle. The path of the groove of a constant force pulley would not fit this definition. The path may not lie on a cone, and the helix angle may not be constant. Helical will be used to differentiate these pulleys from flat pulleys.
For helical constant force pulleys, the radius to the groove can be calculated as it was for flat pulleys. Without the limitation on λmax, the radius to the groove and the pulley diameter can be much smaller. The radius to the groove scales as 1/λmax.
One problem that arises with a helical pulley is that the cable can rub on the sides of the groove. For pulleys and capstans, the term “fleet angle”, is defined as the angle between the cable and the tangent to the pulley groove. To limit friction and wear, it's desirable to keep the fleet angle small. This is not always possible, especially with short center distances m1 or m2.
The easiest way of designing the helical groove is to linearly advance the groove in an axial direction as the pulley rotates. This will produce a constant pitch groove. Alternately, the groove can be constructed with a constant helix angle. Both of these methods have fleet angle problems.
A preferred solution is to advance the groove axially at a rate that aims or focuses the tangent to the groove at a single remote point. The groove will start with a large helix angle at the large radius end of the helical pulley. The helix angle will decrease continuously to a small value at the small end of the pulley. A pulley with this type of “focused” groove is shown in
The single groove design eliminates one cable and two cable terminations. The loads and stresses produced by the cable terminations are eliminated. With the lower stress, the pulleys can be constructed from lower strength materials including plastics. The plastic may be of a type suitable for bearings. This will eliminate the need for separate bearings. The pulleys can rotate directly on a shaft.
For a single cable mechanism, if the tension ratio between the input and the output falls within the following range, the cable will not slip on the pulley.
e−μθ<Fin/Fout<eμθ
Where μ is the coefficient of friction between the pulley and the cable, and θ is the total wrap angle in radians, of the cable on the pulley. Friction will transfer the entire load between the cable and the pulley. A variety of other methods can be used to keep the cable from slipping. These include using a crimp, a knot, or a bead tied onto the cable. The crimp, knot, or bead can be retained by a slot that crosses the pulley groove. The cable can be jammed into a narrow or serrated slot in line with the pulley groove. Alternatively, the cable can be glued or welded in place.
A helical single groove dual pulley may have two or more parts that can be phased relative to each other as previously described.
Other Options
Dual pulleys can be designed to deliver output force profiles that are not constant. Pulleys can also be designed to accept other spring force profiles.
In this disclosure, the input and output pulleys are rigidly coupled. The pulleys can also be designed to work on two different axes similar to the prior art in
The differential spline hub will work with other numbers of splines on each end.
The pulley v-grooves can be eliminated for some applications. For example, a flat strap can be used on a flat pulley surface. Chains can be used with toothed pulleys.
Smaller, Lighter, Less Inertia, Longer Cable Life, Higher Load, and Better Balance
The composite torque profile minimizes the size of the pulleys. With smaller pulleys, less space is required, the pulleys are lighter, and they have much less rotational inertia.
Cable life and load can also be improved. Pulley size, cable life, and operating load are all related. The cable life is improved by increasing its bend radius and by decreasing the cable load. The bend radius is equal to the radius of curvature of the pulley, not the pulley radius. For a given pulley size, the composite torque profile maximizes the pulley radius of curvature. For a given pulley size, the composite profile also maximizes the input cable travel L1. This reduces the spring and cable force. The lower force and the larger radius of curvature increase the cable life.
The composite torque profile pulleys are easier to balance. Compared to previous spiral pulleys, their center of gravity is closer to the axis of rotation. This makes it easier to balance the pulleys for greater force accuracy and less vibration.
Modular, Standardized, Low Cost, and Easy to Use
A small number of standardized input and output pulleys with symmetric torque profiles can be used to cover a wide range of constant force applications, from low force to high force and from short stroke to long stroke. Pairs of input and output pulleys can be used in combination with thousands of available extension springs. For a given output force and stroke, the spring can be selected for the required cycle life. Within limits, the spring length and outside diameter can be selected to fit the available space. Selecting appropriate input and output pulleys is a simple process. For most applications, a custom design isn't needed. The small number of pulley sizes needed to cover a wide range of applications should make it feasible to mass produce the pulleys at low cost.
The differential spline hub gives the freedom to orient the spring and the output cable where they fit best. With the hub, the pulleys can be rapidly and accurately assembled with high angular resolution.
Better Accuracy
A dual pulley mechanism can deliver an output force more accurately than a constant force spring. The force from a constant force spring fluctuates due to local geometric variations along the spring. Local variations along the length of a helical spring do not produce the same force variations.
The force error of a pulley mechanism is a linear function of the pulley profile. For example, if the pulley radius is 10% larger than it should be, the resulting force error will be 10%. The force error for a constant force spring is a cubic function of the spring thickness. A 10% thickness error will produce a force error of about 33%.
If a specific force is required from a dual pulley mechanism, an end plug can be used to adjust the helical spring. The output force can be adjusted to within a fraction of one percent. An expensive tight tolerance spring is not required. The tolerance for a constant force spring is typically about + or −10%.
Lighter Weight and Longer Life Spring
Helical extension springs are ideal for the dual pulley constant force mechanism. When operated at similar stress levels, helical springs can store approximately twice as much energy per pound compared to constant force springs. Constant force springs typically have a relatively low cycle life between 4,000 and 40,000 cycles. Helical springs can be designed for a much longer life.
Fusee Advantages:
Smaller Size, Fewer Parts, Less Wear and Friction, and Less Sensitive to Alignment Errors
The outside diameter of the spiral pulley can be reduced by increasing the total rotation of the pulley. A multiturn spiral pulley is called a fusee. The fusee diameter can be much smaller than an equivalent flat spiral pulley. The fusee will be wider than the flat pulley.
A fusee is less sensitive to angle errors and to errors in the center distance m. With a larger total angle of rotation, the fusee radius changes more slowly. As a result, the fusee is less sensitive to angular alignment errors. When a cable wraps onto a variable radius pulley, the cable direction changes. The direction change is a function of both the center distance m and the total radius change of the pulley. A fusee with a greater total rotation will have a smaller radius change than an equivalent flat pulley. As a result, the fusee is less sensitive to center distance errors.
The focused groove aims the fusee groove at a remote point. This reduces the cable friction and wear.
The input and output grooves can be combined into one continuous groove. Only one cable is needed for the mechanism. With only one cable, the cable terminations can be eliminated. The stress produced by the cable terminations is eliminated too. With lower stress, the fusee can be made from a less expensive material. The fusee can be molded out of plastic. With a suitable plastic, the fusee can rotate directly on the shaft. Additional bearings aren't needed.
The fusee can be made in one piece. It can also be made in two or more parts, with the input pulley in one part and the output pulley in another part. A spline mechanism can be used to adjust and align the parts.
This application claims benefit to U.S. Provisional Application No. 60/460,771, filed Apr. 4, 2003, which is incorporated herein by reference in its entirety.
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| 60460771 | Apr 2003 | US |
