The present invention concerns rotational motion controlling mechanism, rotational motion controlling method and an escapement gear wheel. More particularly, the invention is related to rotational motion of a drum or a spool during unrolling from it a wound tubular strip and serves for unrolling speed control.
Tubular strips, i.e. strips which in the relaxed state are curled along its tubular axis, have numerous applications in booms, manipulators and antennas, especially in space applications. For example, a hardened strip wound curled into a tube after stretching out and winding onto a spool has small size and weight. Unrolled from the roll it curls around the axis passing through the centre of the strip. This way, after unrolling the strip from the spool a structure constituting a thin-walled tube reappears, characterised by a very good flexural strength to weight ratio. The thickness of the strip the tube is made of is strongly dependent on the planned application, planned length of the tube and targeted loads.
Small weight and the possibility of tight “packing” of a long element and also the possibility of smooth adjustment of its length decide about the exceptional usefulness of structures made of curled strips in space applications. The devices intended for operation in space face much more strict requirements than terrestrial devices. Delivery of the structure at its destination site is an additional problem, which has to be considered already at the design stage. For carrying the structures to the mission site rockets are used, the carrying capacity and cargo space of which are very limited. Due to this, maximal reduction of the device's weight and the possibility to fold into a small volume and later to deploy after reaching the target is required.
For example, a solution wherein curled strips mechanism has been used is a manipulator, combining long reach with a small weight and small size in folded state, disclosed in document U.S. Pat. No. 3,601,940. In folded state the working strip, typically made of metal, is wound on a rotated spool. Specific cross-section of the strip causes, that when not held by the spool it curls around an axis passing through the centre of the strip. This way, after unrolling the strip from the spool a structure resembling a thin-walled tube appears. Thus, there is formed an element the length thereof can be adjusted in a significant range by winding and unrolling the strip from the spool. Similar solutions have been disclosed in other documents, like e.g. in U.S. Pat. No. 3,434,674. In this document preferable ranges of thickness of the strips have been indicated and the most typical materials for their construction have been listed. Among them are: carbon steel, stainless steel, beryllium bronze, titanium alloys and fibre composites (e.g. glass or carbon fibres) like e.g. carbon fibre reinforced polymer (CFRP).
Reliable unwinding of strips in structures of booms, antennas and a manipulator is very important in space applications, because the possibilities of repairing the structure or manual deployment after launching from Earth are limited or do not exist at all.
In the report NASA SPACE VEHICLE DESIGN CRITERIA GUIDANCE AND CONTROL entitled “Tubular spacecraft booms (extendible reel stored)”, dated February 1971, there are disclosed typical failures of structures employing curled strips and their causes. Included have been, inter alia, failure of motor driving the spool where the strip has been wound, failure of power supply and jamming of the strip on the spool.
In the strip wound on the spool the is stored energy. In the case of strips made of carbon steel and beryllium bronze the energy allows to self-unroll of the strip. It is very advantageous, since it allows to eliminate the motor, damage of which is one of the most frequent causes of failure, or at least to reduce its function to wind the strip back onto the roll when it is required to adjust its length.
In terrestrial conditions such strip unrolls very abruptly and quickly, reliably. In application at very small satellites or spacecrafts such abrupt deployment of structural element can lead to the loss of stability. On the other hand, in space conditions, frequently after a long flight, elastic properties can be partially lost and a mechanism facilitating the deployment can become necessary. It is an object of the present invention to provide a mechanism controlling the unrolling of the strip with both functions: supporting drawing the strip out of the roll and also restraining the speed of drawing the strip out of the roll.
In the state of the art, for example from the handbook Z. Mrugalski, “Mechanizmy zegarowe”, Wydawnictwa Naukowo Techniczne, Warszawa 1972, there are known various escapement mechanisms enabling temporal locking of a spring driven wheel. In these mechanism an anchor “catching” the escapement wheel has been applied. The anchor has caught the wheel locking it. For this purpose the teeth of the escapement wheel have been inclined at an angle such that the straight line between the tooth's tip and the escapement wheel's axle was not located fully in the escapement wheel and partially passed the space between the teeth. Because of this the end of the anchor's arm introduced between the teeth locks itself the stronger the harder the spring pushes the escapement wheel. In clocks it is released by means of pendulum. Thereby a movement of hands timed by the pendulum is obtained. An attempt to apply such escapement for curled tubular strips would require to expand the mechanism with and additional timing system, possibly being an additional source of failure. Further in the case of partial loss of elasticity by the strip and no possibility of its unassisted unrolling, the mechanism would be useless.
The aim of the invention is to solve the problems highlighted above and to provide such mechanism and method for controlling rotation of an element, which make it possible to control the unrolling of curled tubular strips. Furthermore, the aim of the invention is to provide an escapement wheel, which enables not only restraining of the rotational motion, but also its stimulation.
An element rotation control mechanism according to the invention is suitable for controlling of unrolling of the curling strip rolled on a drum, the mechanism comprising an escapement gear wheel (2) fixed at the axis of rotation of the drum and an anchor. Anchor is pivotably mounted at a distance less than half of the span between the first anchor arm and the second anchor arm from the escapement gear wheel so that the first anchor arm and the second anchor arm can come into contact with the escapement gear wheel in alternate manner. Wherein the teeth of the escapement gear wheel have edges shaped so that anchor arm slides on them without locking when the anchor arm and escapement wheel are in contact, so that the rotation of the escapement gear wheel causes swinging motion of the anchor striking the gear wheel alternately with the first anchor arm and second anchor arm reducing therefore the speed of rotation. The radius of the escapement wheel as well as the dimensions and the number of teeth are chosen such that in the position of the escapement wheel, where one of the arms of the anchor has its point of contact with the escapement wheel located exactly at the bottom of the inter-tooth notch, the point of contact of the second arm of the anchor is located at the rear edge of a tooth. The mechanism further comprises an electromagnet and a clamp mounted moveably with respect to it, wherein the clamp is connected to the anchor so that turning the electromagnet on enforces movement of the clamp, that presses the first arm of the anchor against the escapement gear wheel, and a return spring connected with the anchor, mounted so that it counteracts the force exerted on the anchor by the electromagnet via the clamp, wherein the tension force of the spring is less than the force of the electromagnet.
Preferably the teeth of the escapement wheel have substantially the shape of an acute-angled triangle with sides of different length, and n+½ teeth are accommodated on the arc segment of the escapement wheel bounded by the point of contact of the first arm of the anchor with the escapement wheel and the point of contact of the second arm of the anchor with the escapement wheel, where n is a natural number.
Preferably the frontal edges of teeth are inclined at an angle within the range of 20° to 30° with respect to the straight line connecting the tip of the tooth with the centre of the escapement wheel, and rear edges of teeth are inclined at an angle within the range of 50° to 60° with respect to the straight line connecting the tip of the tooth the centre of the escapement wheel.
Preferably the escapement gear wheel has 25 to 35 teeth.
An element rotation control method according to the invention is used with a mechanism for controlling of unrolling of the curling strip rolled on a drum having an escapement gear wheel fixed at the axis of rotation of the drum. The mechanism further has an anchor pivotably mounted at a distance less than half of the span between the first anchor arm and the second anchor arm from the escapement gear wheel so that the first anchor arm and the second anchor arm can come into contact with the escapement gear wheel in alternate manner. The teeth of the escapement gear wheel have edges shaped so that anchor arm slides on them without locking when the anchor arm and escapement wheel are in contact. The radius of the escapement wheel as well as the dimensions and the number of teeth are chosen such that in the position of the escapement wheel, where one of the arms of the anchor has its point of contact with the escapement wheel located exactly at the bottom of the inter-tooth notch, the point of contact of the second arm of the anchor is located at the rear edge of a tooth. The mechanism further comprises an electromagnet and a clamp mounted moveably with respect to it, wherein the clamp is connected to the anchor so that turning the electromagnet on enforces movement of the clamp, which moving presses an arm of the anchor against the escapement gear wheel and a return spring connected with the anchor, mounted so that it counteracts the force exerted on the anchor by the electromagnet via the clamp, wherein the tension force of the spring is less than the force of the electromagnet. The method comprises a step of periodically turning on the electromagnet to accelerate unrolling of the curling strip when it stops unrolling itself.
Preferably the teeth of the escapement wheel are chosen such that they have substantially the shape of an acute-angled triangle with sides of different length, and n+½ teeth are accommodated on the arc segment of the escapement wheel bounded by the point of contact of the first arm of the anchor with the escapement wheel and the point of contact of the second arm of the anchor with the escapement wheel, where n is a natural number.
Preferably the teeth of the escapement wheel are chosen so that the frontal edges of the teeth are inclined at an angle within the range of 20° to 30° with respect to the straight line connecting the tip of the tooth with the centre of the escapement wheel, and the rear edges of the teeth are inclined at an angle within the range of 50° to 60° with respect to the straight line connecting the tip of the tooth with the centre of the escapement wheel.
Preferably the escapement gear wheel is chosen such that is has 25 to 35 teeth.
The invention has been explained in embodiments presented with reference to the drawings, wherein
The mechanism controlling the unrolling of the elastic strip from the spool has been shown in perspective in
In
In the case of assisted motion, the stimulated oscillatory moves of the anchor 1 and its arms' ends into the teeth of the escapement wheel enforce the rotational motion of the escapement wheel in the case when the elastic energy stored in the strip is insufficient for self-unrolling. For stimulation of the anchor's movement a number of available technical means can be used, for example, the arrangement of an electromagnet and a spring, not shown in
The span of the arms of the anchor 1, the shape and the number of teeth and the radius of the escapement wheel 2 are carefully chosen. Let us consider an arc of the escapement wheel limited at one end by the point, where the first arm 11 of the anchor 1 contacts the wheel, and at the other end by the point, where the second arm 12 of the anchor 1 contacts the wheel. On this arc there is located a non-integer number of teeth. Therefore, if one of the anchor's arms contacts the wheel exactly at the tip of a tooth or in a point located exactly between two teeth, i.e. in such places, where an arm striking cannot enforce movement of the wheel, then after rotation of the anchor the second arm will always hit a tooth's edge. Such arrangement causes, that the wheel's teeth striking alternately the arms 11 and 12 of the anchor enforce its swinging motion.
Furthermore, such configuration helps to avoid the situation, when none of the anchor's arms can enforce the movement of the wheel 2 in the case of stimulation of oscillatory movement of the anchor by means of the electromagnet 3 and the spring 5.
The use of asymmetric triangular teeth makes it possible to enforce by the anchor the movement in a defined direction. If the teeth are asymmetric and between the points defined on the wheel 2 by the arms of the anchor 1 there are accommodated ca. n+½ teeth, where n is a natural number, then in the movement stimulated by alternating rotation of the anchor, the ends of the anchor will always fall on the rear edges of teeth. A half of a tooth is defined by the line being the bisector of the angle defined by the centre of the escapement wheel and two adjacent inter-tooth notches.
Those skilled in the art of clockworks are capable of choosing without problems the pressing force of the electromagnet 3 and the spring 5, the shape and the number of the teeth of the escapement wheel 2 and the shape of the ends of the arms 11 and 12 of the anchor 1 and their span so that the anchor 1 being pressed against the escapement wheel 2 by the electromagnet 3 or the spring 5 jammed or not. Detailed information on this subject can be found in the handbook Z. Mrugalski, “Mechanizmy zegarowe”, Wydawnictwa Naukowo Techniczne, Warszawa 1972. This reference fully complements the disclosure of the invention. Alternative shapes of the teeth, for example with convex, rounded edges can be used to reduce the risk of the mechanism jamming.
Unassisted rotation has been shown in
The assisted unrolling of the strip has been shown in
In the first phase, shown in
The inventors have observed, that the above described operation of the escapement wheel 2 and its cooperation with the anchor 1 can be obtained when the frontal edges of escapement wheel's teeth are inclined at an angle within the range of 20° to 30° with respect to the straight line connecting the tip of a tooth with the centre of the escapement wheel 2, and the rear edges of the escapement wheel's teeth are inclined at an angle within the range of 50° to 60° with respect to the straight line connecting the tip of a tooth with the centre of the escapement wheel 2. For this range of values it is easy to obtain the effect of not jamming the anchor.
A particularly preferable embodiment of the escapement wheel has been shown in details in
Escapement gear wheels with a large number of teeth are difficult to produce. However, with a too low number of teeth the movement of the strip is not smooth. Furthermore, with a low number of teeth the teeth have to be bigger, thus in turn enforcing a large range of movement of the anchor. The large range of movement of the anchor means that the clamp 4 in its terminal position is further from the electromagnet 3. This in turn makes it necessary to use a bigger and stronger electromagnet and increase the dimensions of the device. It follows from experiments that the optimal number of teeth is between 25 and 35.
An additional advantage of using the mechanism according to the invention for control of unrolling speed of tubular strips is that in the case of jamming the strip it is possible to use the electromagnet with high frequency excitation to generate a series of shaking moves, which allow to gradually rotate the drum and unlock the jammed strip.
Number | Date | Country | Kind |
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PL405646 | Oct 2013 | PL | national |
Filing Document | Filing Date | Country | Kind |
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PCT/IB2014/062651 | 6/27/2014 | WO | 00 |