Device and method for selectively milling the surface of a roadway

Abstract

A device for cutting rumble strip grooves in a roadway. The device includes a cutter head on which is mounted a plurality of cutting teeth. The cutter head is symmetrically disposed around a center axis. At least one motor is provided for rotating the cutter head about its center axis. In addition to the motors that directly rotate the cutter head, a mechanism is provided for cycling the center axis of the cutter head through a continuous pathway. Accordingly, the cutter head experiences two separate rotations. The cutter head rotates about its own center axis. Meanwhile, the center axis is orbiting in a circular pathway. As the cutter head cycles through part of the continuous pathway, the cutter head contacts the roadway and cuts a rumble strip groove in the roadway.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to machines that are designed to remove material from the surface of a roadway with a rotating milling head. More particularly, the present invention relates to such machines that can be configured to create parallel grooves in a roadway that can act as rumble strips.

[0003] 2. Prior Art Statement

[0004] Every year many vehicular accidents are caused by drivers who are inattentive or fall asleep while driving. Often, such accidents result in severe injuries or loss of life. Different transportation authorities throughout the country have tried many different programs to reduce the occurrence of such accidents. Many roadside signs have been posted, reminding drivers to stay alert. Flashing lights are used along dangerous parts of many roadways to try to get a driver's attention, and focus that attention on driving. However, such passive devices have only a limited likelihood of success in arousing a sleepy or inattentive driver.

[0005] Recognizing the faults of passive systems, many transportation authorities now use the active system of rumble strips to arouse sleepy or inattentive drivers. “Rumble strip” is the name used in the transportation industry for parallel structures placed in the roadway. The parallel structures can either be depressions that are cut into the surface of the roadway or protrusions that extend above the roadway. Rumble strips are placed on the side of the road to warn a driver that his/her car is wandering off to the side of the road. Rumble strips are also used before tollbooths and other changes in traffic patterns to warn drivers of the upcoming change. When the wheels of a vehicle pass over a rumble strip, the driver of the vehicle physically experiences a high frequency vibration in the vehicle. Additionally, a loud rumbling noise is created by the wheels passing over the rumble strips. The combination of the vibration and the noise actively awakes the driver of the vehicle. This hopefully arouses the driver to a point where the driver can safely operate the vehicle.

[0006] Rumble strips can be created in a roadway as the roadway is being laid or repaved. However, most roadways that are in existence were originally created without rumble strips. Accordingly, on many roadways, rumble strips are retroactively added to the structure of the roadway. Using current technologies, the most cost effective way to create rumble strips in an existing roadway is to cut a series of parallel grooves in the material of the roadway.

[0007] In the prior art, rumble strips on the side of a roadway are traditionally made using a cylindrical cutter. The cylindrical cutter is periodically raised and lowered into the surface of the roadway to cut the desired grooves in the roadway.

[0008] As is well known by machinists, all cutting tools have an ideal work feed rate that optimizes the life of the cutting tool and the quality of the cut being made. If work is fed into a cutting tool too quickly, the life of the cutting tool is dramatically shortened, Furthermore, if work is feed into a cutting tool too quickly, stresses occur in the machine that drives the tool. This can cause the machine to break or prematurely require maintenance. This same principal applies to milling machines that cut rumble strips into the material of a roadway. As has been previously mentioned, milling machines that cut rumble strips on the side of a roadway contain cylindrical cutters. On the exterior of the cylindrical cutter are disposed many individual carbide cutting teeth. If the cylindrical cutter were to be advanced through the hard material of a roadway too rapidly, the carbide cutting teeth may break or wear rapidly. As a result, after only a short period of use, the carbide cutting teeth would have to be replaced.

[0009] To create ideal cutting conditions, a cylindrical cutting head would be set in a stationary position over a segment of roadway and lowered into the material of the roadway at a controlled rate. After a single groove was cut, the cylindrical cutter would be lifted and advanced to the next set location of a cut. However, when creating rumble strips on the side of a road, a rumble strip is formed about every foot. Many hundreds of miles of rumble trips may be required to be installed in a typical construction job. If a milling machine were to be set in place for each cutting of the rumble strip, it would take far too much time to complete the job.

[0010] Recognizing the limitations of time, most all prior art rumble strip milling machines operate using less than ideal cutting conditions. In many prior art rumble strip cutting machines, a rotating cylindrical cutter is attached to a vehicle and is rotated at a fixed revolution rate. The cylindrical cutter is then periodically lifted and dropped into the roadway as the vehicle moves forward. Accordingly, as the cylindrical cutter descends into the material of the roadway, it is also being pulled forward through the material of the roadway, thereby creating an elongated groove. The faster the vehicle moves, the further the cylindrical cutter is pulled through the roadway material and the more elongated the groove becomes.

[0011] If a vehicle travels too quickly, the rate at which the cutting teeth advance into the roadway material may surpass the operational specifications for the cutting teeth. As a consequence, the cutting teeth may break or wear prematurely. Additionally, if the vehicle travels too quickly, the grooves may become so elongated that there is little uncut roadway left between each of the cut grooves. This creates rumble strips that do not match the specifications of the transportation authority that require certain minimum distances between grooves.

[0012] To prevent these problems from occurring, most prior art rumble strip milling machines run at slow speeds where they produce no more than two rumble strips a second.

[0013] A need therefore exists for an improved rumble strip milling machine that can run at higher speeds without creating poorly formed grooves or creating unnecessary wear on the cutting teeth. This need is met by the present invention as described and claimed below.

SUMMARY OF THE INVENTION

[0014] The present invention is a device for cutting rumble strip grooves in a roadway. The device includes a cutter head on which is mounted a plurality of cutting teeth. The cutter head is symmetrically disposed around a center axis. At least one motor is provided for rotating the cutter head about its center axis. In addition to the motors that directly rotate the cutter head, a mechanism is provided for cycling the center axis of the cutter head along a continuous pathway. Accordingly, the cutter head experiences two separate rotations. The cutter head rotates about its own center axis. Meanwhile, the center axis is orbiting in a continuous pathway.

[0015] As the cutter head cycles through a part of the continuous pathway, the cutter head contacts the roadway and cuts a rumble strip groove in the roadway. The cutter head is propelled along a section of roadway by a vehicle. The vehicle moves in a first direction, thereby giving a forward velocity to the cutting head as it cuts into the roadway. The movement of the cutting head as it cycles through its continuous pathway compensates for the forward movement of the cutting head. As a result, the cutting head produces a high quality groove in the roadway with reduced wear on the cutting head and its drive mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a better understanding of the present invention, reference is made to the following description of exemplary embodiments thereof, considered in conjunction with the accompanying drawings, in which:

[0017] FIG. 1 is a side view of one exemplary embodiment of the present invention, shown in operation on a segment of roadway;

[0018] FIG. 2 is a perspective view of the primary rumble strip milling machine components of the present invention;

[0019] FIG. 3 shows the relationship between the cylindrical cutter, the orbital disc and the surface of the roadway as the cylindrical cutter cycles through its continuous pathway of movement;

[0020] FIG. 4 shows the movement of the cylindrical cutter as it contacts and moves through the material of the roadway;

[0021] FIG. 5 shows a graph that plots the position of the cylindrical cutter verses the relative movement of the cutter in relation to the pavement being cut; and

[0022] FIG. 6 shows an exemplary embodiment of the mounting elements that join the rumble strip milling machine to a vehicle.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023] Although the present invention rumble strip milling machine can be configured to be a separate trailer assembly that can be towed behind a powered vehicle, such as a truck, the present invention is particularly well suited to be built as part of a powered vehicle. Accordingly, in the exemplary embodiment of the present invention shown, the rumble strip milling machine is shown as part of a dedicated vehicle in order to set forth the best mode contemplated for the invention.

[0024] Referring to FIG. 1, a first exemplary embodiment of the present invention rumble strip milling machine 10 is shown. The rumble strip milling machine 10 is attached to the undercarriage of a self-powered vehicle 12. The vehicle 12 is a dedicated piece of construction equipment for use only at construction sites. Consequently, the power train of the vehicle 12 is designed to operate at peak efficiency while propelling the vehicle at its operational speeds, which is typically below five miles per hour.

[0025] The rumble strip milling machine 10 is suspended from the bottom of the vehicle 12. The rumble strip milling machine 10 contains a cylindrical cutter 20. A plurality of replaceable cutting teeth 22 are attached to the exterior of the cylindrical cutter 20. The cylindrical cutter 20 rotates in a direction opposite of that of the front wheels of the vehicle 12. Consequently, if the vehicle 12 is traveling forward, the cylindrical cutter 20 shown in FIG. 1 rotates clockwise in the plane of the paper.

[0026] The rumble strip milling machine 10 has a main frame 24 that is suspended below the vehicle 12 a predetermined distance D1 above the level of the pavement 18. This height can be selectively adjusted, as will later be explained. The cylindrical cutter 20 partially extends below the frame 24. The cylindrical cutter 20 periodically moves from a first elevation above the pavement 18 to a second elevation below the plane of the pavement 18. As a result, the cylindrical cutter 20 cuts periodic parallel groves 26 in the material of the pavement 18. The speed at which the cylindrical cutter 20 cycles above and then into the material of the pavement 18 is directly proportional to the forward speed of the vehicle 12. Accordingly, the rumble strip milling machine 10 will create evenly spaced grooves 26 in the pavement 18 even if the speed of the vehicle 12 were to vary.

[0027] Referring now to FIG. 2, the primary workings of the rumble strip milling machine 10 are illustrated. The rumble strip milling machine 10 has a cylindrical cutter 20 that does the cutting. On the exterior of the cylindrical cutter 20 are a plurality of cutting teeth 22. Each of the cutting teeth 22 is individually replaceable. Accordingly, if one cutting tooth were to break, that cutting tooth can be replaced. The cutting teeth 22 on adjacent rows are staggered in position. However, it is preferred that the same pattern of cutting teeth 22 be repeated every 90° on the periphery of the cylindrical cutter 20. In this manner, it is assured that the cutting teeth 22 on the cylindrical cutter 20 will make a full cutting pass for each quarter turn of the cylindrical cutter 20.

[0028] The cylindrical cutter 20 is concentrically mounted to a primary drive shaft 30. The primary drive shaft 30 is connected to at least one drive motor 32. In the shown embodiment, both ends of the primary drive shaft 30 are connected to separate drive motors 32. The use of two drive motors 32 enables a high degree of horsepower to be obtained from two small motors rather than through the use of one large bulky motor. The use of two motors also provides a degree of side-to-side balance to the assembly that prevents wobbling during its operation. The drive motors 32 can be electric motors or combustion motors. However, in the preferred embodiment, hydraulic motors are used because they have a very high power-to-weight ratio. The use of lightweight motors is important to reduce vibrational dynamics, as will later be explained.

[0029] At least one orbiter disc 34 is provided. Each orbiter disc 34 is either a belt wheel or a gear having a circular outer periphery and an inner aperture 36 that is eccentrically positioned relative the circular outer periphery. The primary drive shaft 30 passes through the eccentric inner aperture 36. In the eccentric inner aperture 36 is a bearing pack (not shown) that enables the primary drive shaft 30 to rotate freely within the eccentric inner aperture 36. Since the primary drive shaft 30 passes through the eccentric inner aperture 36 of each orbiter disc 34, each orbiter disc 34 is not symmetrically disposed around the primary drive shaft 30.

[0030] A secondary drive shaft 38 is provided. The secondary drive shaft 38 is coupled to a speed synchronized drive 40. The speed synchronized drive 40 is a drive mechanism that turns the secondary drive shaft 38 at a speed that is directly proportional to the forward speed of the vehicle 12 (FIG. 1). Consequently, the faster the vehicle 12 is moving forward, the faster the speed synchronized drive 40 will turn the secondary drive shaft 38. The speed synchronized drive 40 can be a hydraulic drive, an electric drive or a mechanical drive that is driven by some portion of the power train or wheels of the vehicle 12 (FIG. 1).

[0031] The secondary drive shaft 38 is mechanically coupled to the orbiter discs 34 that are positioned around the primary drive shaft 30. If the orbiter discs are gears, the mechanical connection between the orbiter discs and the secondary drive shaft 38 can be accomplished using connecting gears. However, in the shown embodiment, the orbiter discs 34 are belt wheels. As such, the orbiter discs 34 are connected to smaller belt wheels 42 on the secondary drive shaft 38 with the use of drive belts 44.

[0032] It will therefore be understood that the speed synchronized drive 40 turns the secondary drive shaft 38 at a rotation rate that is directly proportional to the forward speed of the vehicle 12 (FIG. 1). The secondary drive shaft 38 turns the obiter discs 34. The orbiter discs 34 physically move the primary drive shaft 30 through a circular range of motion as the primary drive shaft 30 spins. Accordingly, the cylindrical cutter 20 experiences two rotational motions. First, the cylindrical cutter is rotating around the primary drive shaft 30. Secondly, the primary drive shaft 30 is moved through a circular range of motion by the orbiter discs 34. Consequently, the cylindrical cutter is rotating about a first axis while that first axis orbits around a second axis.

[0033] The cylindrical cutter 20 is rotated around the primary drive shaft 30 by the drive motors. The primary drive shaft 30 and drive motors are orbited in a circular range of motion by the orbiter discs 34. Since the drive motors 32 are orbiting through the circular range of motion, the drive motors 32 become sources of dynamic vibration. By minimizing the weight of the drive motors 32, the degree of dynamic vibration is also reduced. Thus, it is desirable to have very low weight drive motors 32. To counteract the dynamic vibrations created by the movement of the drive motors 32, counterweights 46 are provided. The counterweights 46 are calibrated in size and location to counteract the dynamic vibrations of the moving drive motors 32.

[0034] Referring now to FIG. 3, the movement in the primary drive shaft 30 created by the rotation of the orbiting disc 34 is better understood. By referring to FIG. 3 simultaneously, it can be seen that the center C of the orbiting disc 34 remains at a constant height H1 above the pavement 18 as the orbiting disc 34 is rotated by the secondary drive shaft 38 (FIG. 2). However, the position that the orbiting disc 34 supports the primary drive shaft 30 changes.

[0035] Looking at Position 1 in FIG. 3, the orbiting disc 34 is shown supporting the primary drive shaft 30 at its highest point above the level of the pavement. At this position, it can be seen that the primary drive shaft 30, and thus the center of the cylindrical cutter 20, is supported above the constant height H1 of the center of the orbiter disc 34. In this position, the center of the primary drive shaft 30 and the center of the cylindrical cutter 20 are also vertically aligned with the center of the orbiter disc 34. Once in such an orientation, the cutting teeth 22 on the cylindrical cutter 20 are supported well above the surface of the pavement. Consequently, the cylindrical cutter 20 does not cut into the pavement.

[0036] Referring to Position 2 in FIG. 3, it can be seen that as the orbiter disc rotates 90° in a clockwise direction, the primary drive shaft 30 and the center of the cylindrical cutter 20 are lowered to the same height H1 as the center of the orbiter disc 34. However, the center of the orbiter disc 34 is no longer vertically aligned with the center of both the primary drive shaft 30 and the cylindrical cutter 20. Rather, the primary drive shaft 30 and the cylindrical cutter 20 have moved in the x-axis and are now horizontally aligned with the center of the orbiter disc 34. At this location, the cylindrical cutter 20 is much closer to the surface of the pavement but has not yet made contact with the surface of the pavement.

[0037] Referring to Point 3 in FIG. 3, it can be seen that as the orbiter disc 34 rotates 180° from its starting position in a clockwise direction, the primary drive shaft 30 and the center of the cylindrical cutter 20 are closest to the level of the pavement. At this position, the center of the cylindrical cutter 20 is below the center of the orbiter disc 34. Furthermore, the center of both the primary drive shaft 30 and the cylindrical cutter 20 again vertically align with the center of the orbiter disc 34. As the cylindrical cutter 20 moves into Point 3, it descends below the level of the pavement, thereby creating the desired groove.

[0038] Referring lastly to Position 4 in FIG. 3, it can be seen that as the orbiter disc 34 rotates yet another 90° in a clockwise direction to a position 270° beyond its starting point, the primary drive shaft 30 and the center of the cylindrical cutter 20 are again raised to the same height H1 as the center of the orbiter disc 34. However, the center of the orbiter disc 34 is no longer vertically aligned with the center of both the primary drive shaft 30 and the cylindrical cutter 20. Rather, the primary drive shaft 30 and the cylindrical cutter 20 have moved in the x-axis and are again horizontally aligned with the center of the orbiter disc 34. At this position, the cylindrical cutter 20 has been raised above the surface of the pavement and no longer makes contact with the surface of the pavement. Lastly, the orbiter disc rotates a last 90° and the cylindrical cutter 20 is moved back into the orientation of Position 1.

[0039] Referring now to FIG. 4 in conjunction with FIG. 3, it can be seen that as the cylindrical cutter cycles through the point positions shown in FIG. 3, the center of the cylindrical cutter 20 follows a generally sinusoidal pathway 50 (FIG. 4). Point 1 in FIG. 3 corresponds to the top of a crest in the sinusoidal pathway 50 shown in FIG. 4. Point 3 in FIG. 3 corresponds to the bottom of a trough in the sinusoidal pattern of FIG. 4. Point 2 and Point 4 in FIG. 3, respectively correspond to halfway points where the cylindrical cutter 20 is either ascending a crest or descending a trough in the sinusoidal pathway 50.

[0040] The cylindrical cutter 20 is rotating about its own center. The center of the cylindrical cutter 20 is being orbited around a secondary axis. Furthermore, the cylindrical cutter 20 is attached to a vehicle that has forward velocity. The result of all of these movements creates the sinusoidal pathway of motion shown in FIG. 4. When the cylindrical cutter 20 contacts the pavement, there is a complex degree of relative movements that exists between the cylindrical cutter and the roadway. As soon at the cylindrical cutter contacts the roadway, the cylindrical cutter cuts into to material of the roadway. This cut is elongated by the relative movement between the cylindrical cutter and the roadway caused by the forward velocity of the vehicle that supports the cylindrical cutter. However, due to the secondary orbit motion of the cylindrical cutter, the cylindrical cutter moves back in the direction of the passing payment, thereby reducing the elongation that occurs.

[0041] Referring to FIG. 5, a graph is shown that plots the position of the cylindrical cutter relative to the passing payment. As can be seen from FIG. 5, it can be seen that the cylindrical cutter only periodically descends below the roadway surface. However, when in contact with the roadway surface the cylindrical cutter has very little relative forward movement with respect to the pavement.

[0042] It will therefore be understood that any groove made by the cylindrical cutter does not have a radius of curvature that matches that of the cylindrical cutter. Rather, the radius of curvature of a cut groove is slightly larger than that of the cylindrical cutter. The cylindrical cutter does not just descend directly vertically into the material of the pavement. Rather, the cylindrical cutter moves slightly, in the direction of the passing pavement, as it cuts into the material of the pavement. The movement of the cylindrical cutter dramatically decreases the elongation of the cut groove caused by the forward movement of the vehicle that supports the cylindrical cutter. At a vehicle operational speed of between 2 miles per hour and five miles per hour, the elongation of the groove caused by the forward velocity of the vehicle does not exceed ½ inch.

[0043] Since the movement of the cylindrical cutter compensates for the forward movement of the vehicle, the cylindrical cutter is not significantly pulled through the material of the roadway by the forward movement of the vehicle. The result is that front-to-back movement of the cylindrical cutter as it cuts provides a cutting relief for the cutting teeth. This prevents the cutting teeth from cutting into the material of the roadway at too rapid a feed rate, thereby significantly prolonging the useful life of each of the cutting teeth and reduces the number of cutter teeth that break prematurely.

[0044] Referring now to FIG. 6, it will be understood that the rumble strip milling machine 10 is not rigidly mounted to its support vehicle. Rather, the rumble strip milling machine 10 is supported in a manner that enables the overall assembly to be free floating. In FIG. 6, it can be seen that the weight of the rumble strip milling machine 10 is supported by two primary support arms 52, 54 and a vertical adjustment cylinder 56. The two primary support arms 52, 54 are joined to the frame of the vehicle at pivot points. The vertical adjustment cylinder 56 is coupled to the top of the rumble strip milling machine 10. As a result, as the vertical adjustment cylinder 56 contracts and expands, the two primary support arms 52, 54 rotate about the pivot points, thereby raising and lowering the overall rumble strip milling machine 10 to any selected height.

[0045] The structure of either one or both of the two primary support arms 52, 54 can include adjustable cylinders 58. Such adjustable cylinders 58 can be used to control the pitch, tilt and yaw of the rumble strip milling machine 10 in order to match the contour of a roadway that may be inclined or otherwise sloped.

[0046] Returning to FIG. 1, it will now be understood that the height of the rumble strip milling machine 10 is controlled by the driver of the vehicle 12. Accordingly, should the driver of a vehicle 12 approach a metal expansion joint on a roadway, the rumble strip milling machine 10 can be raised over the expansion joint without the driver of the vehicle 12 ever having to exit the vehicle 12 or even stop the forward progress of the vehicle 12.

[0047] It will be understood that the embodiment of the present invention specifically described and illustrated is merely exemplary and the shown embodiments can be modified in many ways. For example, the rumble strip milling machine can be made part of a cart that is pulled behind a truck. Details such as the length and the diameter of the cylindrical cutter and the rotating speed of the cylindrical cutter can be altered to match the needs of a contractor and the material of the roadway. All such alternate embodiments and variations are intended to be included within the scope of the claims as listed below.

Claims

1. A device for cutting rumble strip grooves in pavement, comprising:

a cutter head having a plurality of cutting teeth thereon, said cutter head having a first diameter and a center axis;

at least one motor for rotating said cutter head about said center axis;

a mechanism for continuously cycling said center axis of said cutter head through a continuous pathway, wherein said cutter head contacts the pavement and cuts a rumble strip groove in the pavement as said cutter head cycles through part of said continuous pathway.

2. The device according to claim 1, further including a vehicle for moving said cutter head along a roadway at a selected forward velocity.

3. The device according to claim 1, wherein said mechanism cycles said central axis of said cutter head through said continuous pathway at a cycle rate that is directly proportional to said selected forward velocity.

4. The device according to claim 1, wherein said cutter head is a cylindrical cutter having a drive shaft coupled to said center axis, wherein said drive shaft is rotated by said at least one motor.

5. The device according to claim 3, wherein said mechanism includes at least one orbiter disc, and each said orbiter disc has a center point, wherein said drive shaft passes through each said orbiter disc at a point eccentric from said center point.

6. The device according to claim 5, wherein each said orbiter disc is free to rotate about said drive shaft, independent of said drive shaft.

7. The device according to claim 6, wherein said mechanism includes a power source to rotate said orbiter disc, thereby causing said drive shaft and said center axis of said cutter head to move through said continuous pathway.

8. The device according to claim 2, wherein said cutter head cycles through said continuous pathway in the same direction of rotation as the wheels of said vehicle, as said vehicle moves forward.

9. The device according to claim 8, wherein said cutter head is rotated by said at least one motor in a direction opposite the direction of rotation of said continuous pathway.

10. A method of cutting rumble strips in pavement, comprising the steps of:

providing a cutter head;

rotating said cutter head about a central axis;

cycling said central axis through a continuous pathway as said cutter head rotates, wherein said cutter head enters the roadway and cuts a groove in the roadway as it cycles through part of said continuous pathway.

11. The method according to claim 10, further including the step of propelling said cutter head at a selected direction and speed along said pavement as said cutter head rotates and is cycled through said continuous pathway, wherein said cutter head cuts a new section of pavement each time said cutter head cycles through said continuous pathway.

12. The method according to claim 10, further including the step of cycling said cutter head through said continuous pathway at a cycle rate that is directly proportional to said selected speed.

13. The method according to claim 11, wherein said cutting head moves through said continuous pathway in a first direction, as it cuts said groove, wherein said first direction is opposite said selected direction in which said cutter head is propelled.

14. A method of producing rumble strip grooves in pavement, comprising the steps of:

providing a frame;

providing a cutting head having a central axis, wherein said cutting head is supported by said frame;

rotating said cutting head about said central axis;

propelling said frame along the pavement in a first direction at a selected speed, causing relative movement between said cutting head and the pavement;

periodically bringing said cutting head into contact with the pavement, wherein said cutting head is moved through the pavement in a direction that at least in part compensates for said relative movement.

15. The method according to claim 14, wherein said step of periodically bringing said cutting head into contact with the pavement includes cycling said central axis of said cutter head through a continuous pathway, wherein said cutter head contacts and cuts into the pavement while moving through part of said continuous pathway.

16. The method according to claim 14, wherein said step of propelling said frame includes mounting said frame to a powered vehicle.

17. The method according to claim 15, further including the step of cycling said cutter head through said continuous pathway at a cycle rate that is directly proportional to said selected speed.