Boom positioning mechanism

An improved design of positioning mechanism, mountable to an upright, allows smooth, readily accomplished adjustment of the angular, rotational and translational positions of a boom with respect to the upright. A hub is mounted to and rotatable with respect to a base. A friction plate between the base and the hub applies frictional forces that are established by the mechanism, by urging the hub and base together. A pressure sleeve partially contained in a matching opening in the hub controls the rotational and longitudinal movement of the boom with respect to the hub. The design of the frictional engagement surfaces allows adjustment of the resistance to movement of the boom in the angular, rotational and translational directions to extend smoothly and predictably from a condition of virtually no resistance to a completely locked and rigid condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to positioning mechanisms, and in particular to positioning mechanisms for adjustably holding equipments at the desired angular, translational and rotational positions with respect to a mounting support.

2. Prior Art

It is well known for use as equipment support stands to employ a combination of an upright, extending upwardly from a floor base, with a boom mounted to the upright by means of a an adjustable support mechanism, which mechanism allows positioning and holding in position a variety of equipments of the types that may require a variety of large and small position adjustments. The needs for these adjustments may occur frequently and randomly. Such an adjustable apparatus is particularly useful in conjunction with the type of equipment which often requires critical placement, but which also requires adjustment through experimentation, such as microphones, lights, cameras, lamps, gauges, medical instruments and the like.

A variety of stands and positioning mechanisms are presently known and in use for adjustably positioning items carried by such mechanism. However, existing positioning mechanisms are frequently complicated and cumbersome. Such devices all employ some variation of a boom arm carried on an upright, the boom arm being angularly positionable as well as longitudinally positionable with respect to the stand. To fix or lock the boom arm in any desired longitudinal or angular position, various types of locking mechanisms are employed. Regardless of the particular type of locking mechanism used, the prior art devices generally employ multiple separate locking mechanisms, one for the purpose of locking the boom arm against angular movement, and one to lock the boom against translational and rotational movement. As a consequence, the user often has to manipulate at least two separate locking mechanisms to position the equipment at the desired location. The use of the separate locking mechanisms means that the user must deal with them individually at each adjustment.

The existing stands are generally adequate for their intended uses, but there is a need for a mechanism which can position and hold a boom at a wide variety of angles relative to the upright column, allow the extension of the boom outward from the upright column, and allow for rotation of the boom to orient (to aim, for example), the equipment being held, and then to securely hold the boom at any selected angle.

In general, the prior art devices use friction to hold the boom in the desired position. If the prior art locking mechanism is the type having a variable force capability, the friction adjustment may be either loosened, allowing movement of the boom against the frictional force, or increased, effectively preventing the movement of the boom in any direction.

Most of the prior art devices do not aim to achieve, and are not designed to allow for, a controllable application of friction. While it is possible to accomplish some degree of gradual adjustment of the prior art mechanisms by using the method of loosening the prior art friction adjustment, this method is makeshift, at best, because the prior art mechanism is not readily adjustable to a precise force, and the resistance to movement is therefore neither predictable nor finely adjustable.

A need exists therefore for a positioning mechanism having a simple construction which allows precise and repeatable adjustment of the amount of applied friction, in order to allow adjustment of the boom in all three directions of movement: angular, rotational and translational.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide a boom positioning mechanism such that a boom engaged by the mechanism and capable of carrying an equipment at its distal end can be locked against angular, rotational and translational movement by a single locking mechanism.

It is another object of the present invention to provide a boom positioning mechanism that is adjustably movable against precisely adjusted friction forces.

It is another object of the present invention to provide a boom positioning mechanism that having three modes of operation.

It is another object of the present invention to provide a boom positioning mechanism that is easily adjusted by one hand

It is another object of the present invention to provide a boom positioning mechanism that is rugged, durable and foolproof design.

It is another object of the present invention to provide a boom positioning mechanism that is smoothly operable.

It is another object of the present invention to provide a boom positioning mechanism that is relatively fail safe.

It is another object of the present invention to provide a boom positioning mechanism that has precise adjustment capability but is readily manufacturable.

These and other objects of the present invention are accomplished by providing an improved design of positioning mechanism, mountable to an upright, which allows smooth, readily accomplished adjustment of the angular, rotational and translational positions of a boom with respect to the upright. In the present positioning mechanism a hub is mounted to and rotatable with respect to a base, which base is in turn fixed to the upright or another suitable attachment point. A friction plate between the base and the hub applies frictional forces that are established by the mechanism, by means of adjustment of a threaded shaft for example. The hub and base are adjustably compressed to cause the friction plate to frictionally engage the hub and base to control the ease of angular movement. As the compression of the base and hub is adjusted, the friction plate is likewise compressed between them. A pressure sleeve partially contained in a matching opening in the hub controls the rotational and longitudinal movement of the boom with respect to the hub. The external cross section of the pressure sleeve is designed to increase the frictional engagement of the sleeve with the friction plate along its length. The shape of the pressure sleeve and its large contact area with the friction plate causes the translational movement of the boom to be resisted more than is the angular and rotational movement. The design of the frictional engagement surfaces allows adjustment of the resistance to movement of the boom in the angular, rotational and translational directions to extend smoothly and predictably from a condition of virtually no resistance to a completely locked and rigid condition.

DESCRIPTION OF THE PREFERRED EMBODIMENT

General Description of the Positioning Mechanism

Referring now to the figures, wherein like numbers represent like elements throughout the several views,FIG. 1andFIG. 5show an adjustable boom positioning mechanism generally designated by the numeral1.FIGS. 1,2A,2B,3A,3B,4A,4B,6A and6B show the parts and the structure of the positioning mechanism1.

An overall, exploded, perspective view of the positioning mechanism1is shown inFIG. 1. However, as shown inFIG. 5, its use in a commonly encountered application, that of providing support for a microphone4, will aid in understanding the invention.

As shown inFIG. 5, the microphone support comprises a main upright2, and a boom3on which a microphone4is installed. The boom3is mounted to the upright2by means of the positioning mechanism1of the present invention. As mounted, the positioning mechanism1allows the adjustment of the microphone into virtually any position reachable by angular, rotational and translational positioning of the boom. For consistency and convenient reference, the directions of the three movements are defined, as shown inFIG. 5, and detailed further inFIG. 1:1) angular movement—movement of the boom by angular displacement of the hub11, pivoting with respect to the base10, (movement indicator arrow52);2) rotational movement—movement of the boom3around its longitudinal axis (movement indicator arrow51); and3) translational movement—movement of the boom longitudinally, by sliding the boom within and with respect to the positioning mechanism's hub11and by displacement along its length (movement indicator arrow53).

The critical design requirement of the positioning mechanism1is that the design establish the correct relationship among these three forces such that the desired ratios among them are achieved, in turn assuring the desired relationship of ease of movement as to angular, rotational and translational movement of the device with respect to the mounting attachment point, and, reciprocally, the desired ratios of resistance to those movements.

The interrelationship among these forces is controlled such that the angular movement of the boom3is more easily accomplished than rotational movement, and rotational is more easily accomplished than translational movement.

Referring now toFIG. 1, there are shown the major elements of the positioning mechanism1in a disassembled, exploded, perspective view. The positioning mechanism1comprises, in its most essential parts, a base10that ordinarily serves as the fixed side of the mechanism, a hub11that serves as the movable side of the mechanism, and a friction plate13, all concentrically mounted on the axis of shaft15, as well as a friction sleeve14, and pressure pad17mounted to hub11.

Base10and hub11are urged together to compress the intermediate parts, including the friction plate13, friction sleeve14, and friction pad17. Pressure is applied by turning handle16and shaft15to cause the thread28to advance into insert38, thereby cooperating to apply pressure on intermediate parts

Shaft15is an extensive cylindrical member having at least two threaded regions, threads28and threads29, which threaded regions engage the mating threads in threaded insert38and threaded insert39respectively. The threads are coarse, providing for fine adjustment of the forces applied over a small range of motion (approximately 90 degrees) by urging the base10and the hub11together.

Handle16is attached to shaft15by way of insert39, which is locked to the threads29of shaft15by any suitable means, such as a thread-locking compound. Handle16is preferably designed to be easily tightened and loosened by hand, and to be capable of applying a sufficiently large amount of torque to cause the positioning mechanism1to become “locked” when the shaft is fully tightened. When the mechanism1is not locked, controllable pressure may be applied as the base10and the hub11are urged together. The pressure thus applied, due to the design of the pressure controlling elements, is made to be consistent and controllable, as described in more detail below.

Springs19operate on plungers18, all of which are mounted in handle16. Plungers19operate in conjunction with disk42, to cause the handle16to remain in position even when the hub11is being rotated, as described in more detail below.

Base10and hub11are preferably made of aluminum, which is desirable for this application because of its light weight, low cost, capability of relatively low temperature casting, and desirable surface finish options. Because aluminum is not capable of supporting strong threads, steel inserts, such as insert38and insert39, are employed where strong threads are required.

Likewise, aluminum needs additional strength to prevent deformation at locations where high forces are applied. That condition occurs at the point where force from the steel stepped bushing41is applied to the friction plate13. The stepped bushing41has a contacting surface23, not visible inFIG. 1, but shown inFIG. 6B, which cooperates with friction plate13, friction sleeve14, friction pad17, and hub11, all of which, by applying controllable amounts of pressure, produce adjustable and controllable amounts of friction for control of the movement of the boom3and hub11.

To distribute the force applied and to prevent local deformation of the aluminum, the smaller diameter58of stepped bushing41, as shown inFIG. 6B, is pressed into an interference fit in handle16. As the base10and hub11are drawn together, the contacting surface23of the stepped bushing41is urged against the surface22of the friction plate13. The contacting surface23is firmly in contact with the friction plate13when in the fully locked position.

The smaller diameter58of stepped bushing41is made to be a running fit to the bore60in base10through which it passes. The step59in the diameter of the stepped bushing41causes the combination of the stepped bushing41, shaft15and handle16to be held captive in base10. The larger diameter57of the stepped bushing41should either clear or be a sliding fit to all surrounding parts of the base10.

The back side54of the step59in stepped bushing41would wear directly on aluminum it no provision were made to prevent it. Washer49is therefore pressed into an interference fit in base10, so that the side59of stepped bushing41and washer49contact and provide bearing surfaces for one another, whereby washer49prevents steel-to-aluminum contact, for both better wear performance and smoother operation. Washer49also maintains axial alignment of the sub-assembly comprising bushing41, shaft15and handle16.

When the handle16is tightened, the hub11is drawn towards the friction plate13causing the friction sleeve14to tighten and to slightly compress the crowned pressure surface47of friction sleeve14. This causes the friction sleeve14to clamp onto the boom3and ensure that it remains firmly in place.

The base10includes a unique adaptor for attachment to prior art uprights such as upright2. Visible inFIG. 2C, the adaptor includes a partially threaded, slotted socket61, adapted to fit the diameter of the upright2of the usual prior art stands having a tubing exterior diameter of approximately 1.9 cm, and having threads adapted to fit the customary threads of the upright2. The threads62are made to extend over only a portion of the depth of the socket, so that a smooth wall area64of approximately 1.2 cm remains toward the open end of the socket61. A slot63runs over the length of the socket and almost to the end of thread62of socket61. The slot63allows the sides of the socket on each side of the slot to be compressed toward one another. Clearance bores65, shown inFIG. 2B, on one side of the slot63, and threaded bores66on the other side provide means for threaded fasteners67, shown inFIG. 1, to compress the base10on each side of the slot63. When tightened into their matching threaded bores66, the fasteners67reduce the width of the slot63, tightening the sides toward one another and providing secure clamping to the upright2, whether it is threaded or unthreaded.

The slotted socket61is preferably a fairly snug but slideable fit for the outside diameter of the upright2. By maintaining the snug fit, the clear bore64provides a guide for alignment of the upright with the centerline of the threaded portion of the bore, and prevents the cross-threading or mis-threading that is so common in the conventional mounts.

This adaptation also allows the positioning mechanism1to be used in cases where the threads of the upright2are damaged, or the upright has no threads at all.

Once the upright2is inserted into the slotted socket61, if the upright is unthreaded, the clamping action of the fasteners67pulling into the threads66provides the only means to secure the mounting. If the upright is threaded, the clamping action of the fasteners67pulling into the threads66provides stronger and more permanent mounting than the upright threads alone.

The more robust mounting provided by the slotted socket61is advantageous in any application that requires the utmost in strength and security. It is especially appreciated in applications where a performer aggressively handles a microphone, or where especially heavy equipment is to be supported.

Detailed Description—friction Sleeve

Boom3, shown inFIG. 5, is held within friction sleeve14, which sleeve is the only part of the positioning mechanism1that makes direct contact with the boom3. The friction applied by friction sleeve14controls the ease with which the boom may be moved rotationally and translationally with respect to the positioning mechanism1. Its properties are therefore critical in achieving the desired control of frictional forces that are applied to the boom, and that regulate the ease of rotational and translational movement of the boom3.

Friction sleeve14is preferably made of ultra high molecular weight (UHMW) polyethylene, or a similar material having similar characteristics. The important characteristics of the material chosen are: that it retain its memory and flexibility after compression, so that when the applied pressure is released it will quickly, easily, and accurately resume its uncompressed state; that it have the desired blend of the properties of firmness and flexibility, and; that it be readily moldable into fairly complex shapes. If the material is insulating, its insulating property will also provide electrical isolation between the user and the base10of the stand, a factor which may be important in some situations for considerations of signal integrity, or safety, or both.

The geometry of the friction sleeve14is key to the correct operation of the positioning mechanism1. In particular, it is necessary that the frictional force that resists rotational movement and the frictional force that resists translational movement have the desired ratio. In the preferred embodiment, these forces are adjusted such that it is easier to make movement in the rotational direction than in the translational direction.

The friction sleeve14is fitted into a suitably matching cavity21in the hub11. Longitudinal motion of the sleeve14with respect to the hub11must be prevented, so a small dowel24, which engages the sleeve14and a mating cavity21in the hub11, is used to prevent the friction sleeve14from moving within the hub11.

The geometry of the friction sleeve14is the means by which the forces within the mechanism are given the desired balance. Normally, in a sliding fit sleeve, the tightness of the fit, the type of material employed, and the length of the sleeve engaging the boom3are important factors in determining how strongly movement of the boom3is restrained. Although a precise balance of forces could be achieved for a single set of conditions by using a pre-established selections of these factors, the application of this technique would be of limited use because it could only provide a positioning device for one set of boom lengths, equipment weights, and the like. In other words, it would not be adjustable. Moreover, even that single set of conditions would be difficult to control and therefore expensive to accurately reproduce in mass production quantities.

In the preferred embodiment, these frictional forces are established and made adjustable by providing a specially configured cross section of the sleeve, which applies and controls two basic frictional forces:1) the force that resists rotational movement—movement of the boom3around its longitudinal axis (movement indicator arrow51); and2) the force that resists translational movement—movement of the boom longitudinally, by sliding the boom within and with respect to the positioning mechanism's hub11and by displacement along its length (movement indicator arrow53).

The preferred embodiment of the friction sleeve14is shown in detail inFIG. 4AandFIG. 4B. The friction sleeve14has a main interior bore45having a generally cylindrical cross section, and an exterior surface48that follows the cylindrical shape for approximately 180 degrees, then forms a relatively flattened, slightly crowned, crowned pressure surface47. The interior bore45runs the length of the sleeve, and, when under no compression, is a slideable fit to the boom3. Two small grooves46run the length of the friction sleeve14. These grooves are located on the side of the friction sleeve14which is intended to face the friction plate13, and are intended to isolate the crowned pressure surface47from that of the remainder of the sleeve14, so that pressure applied to the crowned pressure surface47does not excessively deform the remainder of the sleeve14. This makes the application of frictional forces by the sleeve14more predictable. The shape of the crowned pressure surface47is adapted to make a broad area of contact with the friction plate13, and to make possible a predictable and controllable application of pressure as the crowned pressure surface47is urged towards friction plate13due to the tightening of the shaft15in the hub11. These forces are adjusted and made to have the desired relationships by making the friction sleeve14conform to the approximate proportions shown inFIG. 4AandFIG. 4B.

Detailed Description—friction plate and Pressure Pad

The angular movement of the boom3is controlled by the frictional forces that resist angular movement of the hub11with respect to the base10. Those forces are a result of the friction of the friction plate13against the crowned pressure surface47and the pressure pad17. Although there is some friction due to contact with the crowned pressure surface47of the friction sleeve14, the main frictional force on the friction plate13that resists angular movement is due to the contact of the friction plate by the pressure pad17. This force is controlled by the rotation of the handle16, and even though there is some contact with the friction sleeve14, this pad force predominates and is relied upon for control.

Pressure pad17is installed in the hub11diametrically opposite to the location of the friction sleeve14. Pressure pad17is preferably of thick laminar shape, having a plan outline that is roughly arcuate so that it generally follows the curvature of the friction plate13and provides maximum contact to the friction plate13, by presenting its complete surface to the plate. A receptacle43contains the pressure pad17by, preferably, an interference fit. The pressure pad17is urged into contact with the friction plate13by hub11being drawn towards the base10.

Friction plate13, preferably made of a highly non-compressible material, such as tool steel, is shown inFIG. 1, andFIG. 6B, which figures illustrate the preferred design. The use of tool steel for the friction plate provides the necessary friction when the friction plate13pressing against the pressure pad17in hub11, and provides in addition a wear resistant face. Friction plate13, preferably force fitted into the base10, preventing its rotation with respect to the base10and thereby providing more predictable friction forces by interaction with the friction sleeve13and the pressure pad17.

When a compressive force is applied to the friction plate13, the force is applied on the side adjacent to hub11by contact with the pressure pad17and the crowned pressure surface47of the friction sleeve14, and on the side adjacent to the base10by the stepped bushing41.

Since the pressure pad is diametrically opposite to the friction sleeve14, a pair of balancing and controllable forces is applied by the friction sleeve14and the pressure pad17on the friction plate13. The friction plate13is normally supported away from the surface of hub11by these forces, and does not, in the unlocked condition, ever make other than incidental contact with the hub11.

Detailed Description—Pressure Springs and Plungers

Located in handle16are plungers18, spring-loaded by springs19, which are so positioned that the plungers are urged toward the base10. Each plunger18/spring19combination is located in its respective receptacle44in handle16, shown inFIG. 6B. Each plunger18/spring19combination is retained by retaining ring50.

Plungers18have a flange68located on the length of the plunger18, which flange68is larger than the diameter of the plunger at either end62or end63, which allows retention of the plunger18and provides a platform against which the spring19pressure may be applied. Each retaining ring50has an inner diameter sufficient to clear the diameter of the plunger18. Each retaining ring50is force fitted into the matching receptacle44, so that the plunger18is loosely contained and its motion is restricted, but each plunger18/spring19combination is still allowed to be compressed and decompressed in response to applied forces.

Spring19, of which there are two identical ones employed in the preferred embodiment, is preferably selected to have an uncompressed length that is large in comparison to its fully compressed length. It is also selected to have an overall length and is to be installed in such a way that in normal operation the spring is always compressed to approximately the mid-point of its maximum compression. During operation, from its most compressed to its least compressed the length of the spring19varies only a small percentage of its total length. By maintaining the spring19within that narrow range, it is made to operate within a narrow range of compression, and therefore maintains a relatively linear coefficient of restitution (spring constant), so that the force it applies gas the positioning mechanism is compressed varies in turn as a fairly linear function of the compression applied by the handle15shaft16.

Plungers18make contact with the washer42, creating a frictional force to prevent the handle16from rotating with the hub11during adjustment of the position of the boom3, or in the event that the boom3is accidentally released while it is being positioned by a user. If accidentally released, the falling boom3will cause the shaft15to rotate in a tightening direction, which causes the positioning mechanism1to tend toward lockup, thereby restraining the fall of the boom3and preventing potential damage to sensitive equipment.

Description of Operation

The operation of the positioning mechanism may be understood by considering separately the three conditions, which shall be referred to as “stages,” into which its operation falls. This operational description begins from an assumed initial condition in which the mechanism is locked. “Locked” in this context means that the handle16has rotated the shaft15to cause the thread portion28, engaged with insert38, to advance into the insert38, urging the hub and base toward one another, and causing the stepped bushing41to make contact with friction plate13to provide the required frictional forces to the parts of the positioning mechanism1. When locked, the compression of the intermediate parts by hub11and base10resists all movement, against normal manually applied forces, in any of the three directions of movement, angular, rotational or translational, as defined above.

The present design makes the application of friction forces by the friction sleeve14adjustable as a function of the force applied by the base and hub. Under a no-pressure condition (i.e.: the hub and base are maximally loosened) the design provides a loose sliding lit between the sleeve14and the boom3. As pressure is applied by compressing the hub and base together, the friction plate13frictionally engages surface47.

Thus, the friction forces applied by the friction sleeve14are a function of the pressure that is externally applied to the sleeve, and makes the forces adjustable over a wide range.

From the locked condition, handle16will be gradually rotated in the loosening direction (preferably counter clockwise as viewed from the handle16end of the shaft15) reducing the force exerted on the hub11and base10, and causing force on the internal parts to be similarly reduced. As these forces are progressively reduced, there may be separately considered three stages:

In Stage One, the pressure applied by the rotation of the shaft15/handle16has been reduced from the fully locked condition. This makes possible angular movement through an arc that is centered approximately on the axis of shaft15. Once the boom3has been positioned, the friction forces are sufficient to maintain its position without re-tightening shaft15/handle16(the braking action).

In Stage Two, the shaft15/handle16combination has been loosened somewhat more than in Stage One. Due to the balance of friction forces described above, the boom3maintains the ability to readily make angular and rotational adjustments as in Stage One. The lesser force applied to the side of friction sleeve14allows the same braking action described in Stage One to minimize free angular and rotational movement of boom3.

In Stage Three the user loosens the shaft15/handle16still more than in Stage Two. The user can then move the boom3angularly, can rotate the boom3within the friction sleeve14, and can slide the boom longitudinally within the friction sleeve14, with only slight resistance. However, the same braking action described in Stage One and Two operates to minimize free translational movement of boom3, and to lessen free fall of the boom3.

From analysis of the mechanism, it may be seen that these three Stages are the result of the design of three distinct parts of the mechanism, in which parts forces are selectively created that are used in order to control the frictional forces that apply to, and thereby resist or prevent movement of the boom. The positioning mechanism1thereby controls the ease of movement of the boom3. The unique operation of the device depends upon relationships among these parts and the three distinct frictional forces that they create.

Although the present invention has been described in connection with an example of the preferred embodiment thereof, it will be appreciated by those skilled in the art that the present invention is not limited merely to those embodiments shown. Many variations and modifications can be made without departure from the spirit of the present invention. For example, the materials, the particular shapes, and the arrangement of the base10and the hub11, and the arrangements of the friction sleeve14and its matching opening in the hub11, as well as their particular locations, can be changed from those which are illustrated. When the boom3is long or its weight is great, a larger frictional force is required to prevent the boom3from sagging down. This may require that the positioning mechanism itself be made larger. These and other variations are specifically contemplated. Accordingly, variation of the preferred form and the particulars as described for the present invention may be undertaken without departure from the scope of the invention, which is defined only by the claims which follow.