GB2503666A - A method of alerting an individual to the impending birth of an animal - Google Patents

Abstract

A method of alerting a responsible individual to the impending birth of an animal comprising the initial step of releasably mounting a birthing sensor 1 onto the tail of a pregnant animal adjacent the body of the pregnant animal, the birthing sensor comprising a sealed casing 3 having a power supply 23,25,27, a wireless communication module 45, a memory, a controller 41 and a movement sensor 43 therein, and thereafter carrying out the steps of monitoring the movements including the tail movements of the pregnant animal with the tail mounted movement sensor. Processing the movements including the tail movements of the pregnant animal monitored with the tail mounted sensor. Comparing the processed movement including the tail movements of the pregnant animal monitored with the tail mounted sensor with at least one impending birth indicator. And on matching the processed movements including the tail movements of the pregnant animal with the impending birth indicator, alerting a responsible individual of the impending birth.

Description

"A method of alerting an individual to the impending birth of an animal"

Introduction

This invention relates to a method of alerting a responsible individual to the impending birth of an animal. More specifically, the present invention relates to a method of alerting a responsible individual to the impending birth of a calf to a cow or heifer.

When a cow or a heifer is in calf, it is important to monitor them closely and be present when they go into labour. If present, the farmer or veterinarian can assist in the delivery of the calf particularly if complications should arise, thereby ensuring a lower mortality rate of newborn calves. Various birthing sensors and methods have been devised for predicting when an animal is about to go into labour and for providing the farmer or veterinarian with a warning that the labour is imminent.

One type of system and method comprises a temperature probe that may be periodically inserted into an orifice of the animal and from their temperature, a prediction can be made as to when the animal is most likely to go into labour. A disadvantage of this type of system and method is that it requires frequent monitoring of the animal by the farmer or veterinarian which is time consuming and inconvenient. Another type of system and method comprises inserting a probe quasi-permanently in an orifice of the animal and receiving measurements from the probe over a radio network. A disadvantage of this type of system is that it may require intervention from a veterinarian in order to insert the probe. Another disadvantage of this type of system is that it is unhygienic to use the probe on more than one animal and therefore if there are many animals to monitor, the cost of monitoring the herd can be significant.

A further type of system and method comprises strapping a movement sensor around the body of the animal and monitoring their movements. Although this system and method overcomes some of the disadvantages of the other quasi-permanent systems in that it allows the sensor to be re-used and does not require the intervention of a skilled veterinarian to put in place, it is prone to damage and to becoming dislodged by the animal wearing the sensor. Furthermore, this system and method suffers from a common problem shared by all of the above-identified systems in that they are not very accurate. Usually, the known systems will only provide the responsible individual with a rough approximation of when the birth will occur, for example, that the birth may occur at any stage over the next 6 hours or so. This means that the farmer or veterinarian may be called out in the middle of the night for a birth that is still several hours away. This is highly undesirable.

It is an object of the present invention to provide a method and system that overcomes at least some of the problems with the known methods and systems. In particular, it is an object of the invention to provide a method and system that requires the least interaction and time of the farmer oi veterinarian by being simple to install and by pioviding an accurate alert that the biith is a short time period away. It is a furthei object of the piesent invention to provide a method and system that offer a useful choice to the consumer.

Statements of Invention

According to the invention there is provided a method of alerting a responsible individual to the impending birth of an animal comprising the initial step of: releasably mounting a biithing sensor onto the tail of a piegnant animal adjacent the body of the pregnant animal, the birthing sensoi comprising a sealed casing having a power supply, a wireless communication module, a memory, a contioller and a movement sensor theiein; and thereafter carrying out the steps of: monitoring the movements including the tail movements of the pregnant animal with the tail-mounted movement sensor; processing the movements including the tail movements of the pregnant animal monitored with the tail mounted sensor; comparing the processed movements including the tail movements of the pregnant animal monitored with the tail mounted sensor with at least one impending birth indicator; and on matching the processed movements including the tail movements of the pregnant animal with the impending birth indicator, alerting a responsible individual of the impending birth.

By having such a method, it will be possible to install the birthing sensor quickly without the intervention of a skilled veterinarian. By monitoring the animals movements including in particular the tail movements, as opposed to monitoring the temperature of the animal or another set of animal characteristics such as heart rate, it is possible to provide a simpler, more reliable system and method than was heretofore the case that will provide the responsible person with an alert that the birth will be within a short time period.

In one embodiment of the invention there is provided a method in which the step of monitoring the movements of the pregnant animal with the tail mounted sensor comprises periodically calculating the pitch angle of the animal's tail with respect to level ground. The pitch angle is a good indicator of whether or not a cow, for example, is going into labour or indeed is in labour. The cow will typically raise and lower its tail a number of times and will keep it in a raised position for an extended period of time prior to giving birth to a calf.

In one embodiment of the invention there is provided a method in which the step of monitoring the movements of the pregnant animal with the tail mounted sensor comprises periodically calculating the roll angle of the animal's tail with respect to level ground. The roll angle will give a good indication of whether or not the animal is standing or lying down or whether the animal has transitioned from standing to sitting or vice versa. If it is detected that the animal has lay down and stood up on a number of times in a given period, it is possible to predict an impending birth.

In one embodiment of the invention there is provided a method in which the step of processing the movements of the pregnant animal monitored with the tail mounted sensor comprises averaging the monitored movements over a first time period. By averaging the movements over a first time period, a number of samples may be obtained and a value will be provided that is representative of the animal movement pattern over the period of time rather than at a specific moment in time. The averaging will also assist in removing many standard actions of the animal and movements experienced by their tail. For example, averaging will assist in minimizing the effects of tail swishing from side to side as the movements are effectively equal and opposite and will cancel each other out. What is left is the orientation of the animal rather than the individual movements.

In one embodiment of the invention there is provided a method in which the first time period is at least 15 seconds in duration. The first time period may be up to 60 seconds in duration. It is envisaged that a sample will be taken four times every second.

In one embodiment of the invention there is provided a method in which the step of piocessing the movements of the pregnant animal monitored with the tail mounted sensor comprises filtering the averaged monitored movements to remove any low frequency components. By filtering the averaged monitored movements, this will also help to reduce any outlying activity that it is not desired to capture and consider in the results.

In one embodiment of the invention there is provided a method in which the step of monitoring the movements of the pregnant animal with the tail mounted sensor comprises capturing acceleration samples with an accelerometer. This is seen as a particularly simple method of capturing the movements of the animal's tail. The accelerometer is a reliable, very inexpensive device to use. Other means, such as, but not limited to an angular rate sensor or a capacitive sensor may be used in its place.

In one embodiment of the invention there is provided a method in which the step of processing the movements of the pregnant animal monitored with the tail mounted sensor comprises: filtering the averaged acceleration samples to remove any low frequency components; calculating the modulus of the filtered average acceleration samples; and summing the moduli over a second time period greater than the first time period; and in which the step of comparing the movements of the pregnant animal monitored with the tail mounted sensor with at least one impending birth movement pattern comprises: comparing the summed moduli with a threshold value representative of a birth indicator; and on the summed moduli exceeding the threshold value, determining that there is a match of the birth movement indicator.

This is seen as a particularly efficient way of determining whether or not an animal is going into labour. Effectively, the energy of the animal's tail movements is captured and if the energy exceeds a predetermined energy threshold value (which is effectively the impending birth indicator), the alert is sent to the responsible individual.

In one embodiment of the invention there is provided a method in which the movement sensor is a three axis accelerometer and the tail movement of the pregnant animal is monitored in at least two axes. In this way, it is envisaged that a more reliable device will be produced. By monitoring the energy in two axes, there will be less chance of a false alarm as there will have to be energy above a certain threshold in each axes or indeed an overall combined energy value in order to trigger the alert. By monitoring the movement of the tail in all three axes, the birthing sensor will be able to detect the raising of the tail when the cow is standing upright or lying down on its side. Furthermore, the birthing sensor will also be able to detect movements of the rear of the animal upwards or downwards as the animal arches its back which can assist in the determination of whether or not the animal is going into labour and finally, the sensor will be able to differentiate between movements of the tail on its own and movements of the cow generally.

In one embodiment of the invention there is provided a method in which the step of comparing the monitored pregnant animal movements with at least one impending birth indicator comprises the birthing sensor comparing the monitored pregnant animal movements with an impending birth indicator stored in memory. In this way, the system can effectively operate as a stand-alone system and the birthing sensor can monitor and detect an impending birth. When the birthing sensor detects an impending birth, it will send an alert, preferably via SMS or other communication over the GSM network to the responsible individual.

In one embodiment of the invention there is provided a method in which the step of alerting a responsible individual of the impending birth comprises the birthing sensor using the wireless communication module to transmit an alert to the responsible individual.

In one embodiment of the invention there is provided a birthing sensor for mounting on the tail of a pregnant animal comprising a sealed casing configured to be mounted on the tail of the animal and a securing strap to hold the casing in position on the tail of the animal, the sealed casing having a power supply, a memory, a wireless communication module, a movement sensor for detecting movement in at least one axes, and a controller therein, the controller being operable to receive measurements taken by the movement sensor! generate a birthing report and pass the birthing report onwards to the wireless communication module for transmission of the birthing report to a remote location. This is seen as a very simple compact birthing sensor to use that will be simple to install and effective in operation. Such a birthing sensor will provide the responsible person with a warning that the impending birth will be within a much tighter time frame than the other known devices and methods.

In one embodiment of the invention there is provided a birthing sensor in which the wireless communication module is a GSM modem capable of transmitting the birthing report to a mobile phone of the farmer or veterinarian over the GSM network.

In one embodiment of the invention there is provided a birthing sensor in which the controller and memory are provided by a microcontroller.

Detailed DescriDtion of the Invention The invention will now be more clearly understood from the following description of some embodiments thereof given by way of example only with reference to the accompanying drawings, in which:-Figure 1 is a perspective view taken from one end of a birthing sensor for use in the method according to the invention; Figure 2 is a perspective view taken from the opposite end of the birthing sensor; Figure 3 is a perspective view taken from below of the birthing sensor; Figure 4 is another perspective view taken from below of the birthing sensor; Figure 5 is a bottom plan view of the birthing sensor; Figure 6 is an end view of the birthing sensor; Figure 7 is a side view of the birthing sensor; Figure 8 is an end view of the birthing sensor showing the opposite end to that shown in Figure 6; Figure 9 is a top plan view of the birthing sensor; Figure 10 is a side cross-sectional view along the lines A-A of Figure 9; Figure 11 is an end cross-sectional view along the lines B-B of Figure 9; Figure 12 is an exploded view of the birthing sensor; Figures 13(a) to 13(c) are diagrammatic representations of a cow having the birthing sensor mounted on it's tail; Figure 14 is an enlarged view of the circled portion C in Figure 13(c); Figure 15 is a cross-sectional view along the lines D-D of Figure 14; Figure 16 is a diagrammatic representation of a cow with the birthing sensor on its tail similar to Figure 13(c) but with the tail of the cow in a raised position; and Figure 17 is a diagrammatic representation of the system in which the method and the birthing sensor according to the invention operate.

Referring to Figures 1 to 12 inclusive, there is shown a birthing sensor, indicated generally by the reference numeral 1, for use in the method according to the invention comprising a sealed casing 3 having a top 5, a bottom 7, a pair of longitudinal sides 9, 11 and a pair of lateral ends 13, 15. A pair of securing strap engagement means are provided, one on each longitudinal side of the casing. The securing strap engagement means each comprise a channel-shaped flange 17, 19 that extends outwardly from the longitudinal side of the casing and is configured to releasably engage a resiliently deformable continuous securing strap (not shown). The channel-shaped flange 17, 19 extend substantially the entire length of the casing 3.

The bottom 7 of the casing is provided with a channel 21 indent that extends along the length of the casing. A padding layer and a non-slip layer, neither of which are illustrated, are preferably mounted in the channel 21. Referring specifically to Figures 10 to 12 inclusive, it can be seen that internal the casing there is provided a power supply, in this case provided by way of three batteries 23, 25, 27 and a circuit board 29 on which there is mounted sensing components including a microcontroller 41, a movement sensor 43 provided by way of a three axis accelerometer, and a wireless communications module 45. The movement sensor 43 detects the movements of the animal and in particular the movements of the animal's tail and determines whether, from those movements, that the animal is in labour. If it is determined that the animal is in labour, an alert is transmitted to the farmer or a veterinarian.

Referring now to Figures 13(a) to 17 inclusive, there are shown various representations of the birthing sensor being mounted on the tail 30, of a cow! 32. First of all, in order to mount the birthing sensor on the tail of a cow, the birthing sensor casing 3 is brought into engagement with the tail of the cow, as illustrated in Figure 13(a), until it is in the desired location on the cow's tail, as illustrated in Figure 13(b). The birthing sensor casing 3 is held in that desired position by the operator (not shown) with one hand while their other hand is used to affix a resiliently deformable continuous securing strap 31 to one of the channel-shaped flanges 17, 19 that extend outwardly from the longitudinal side of the casing 3. When the securing strap 31 has been connected to the channel shaped flange 17, 19, the securing strap 31 is then led around the tail of the animal and secured in place on the other channel shaped flange 17, 19, thereby trapping the tail of the animal intermediate the continuous securing strap and the bottom of the casing, as shown in Figures 13(c), and 14 to 17 inclusive.

The securing strap 31 is preferably a continuous ring of rubber or similar rugged, resiliently deformable material. The securing strap 31 will hold the casing in position on the cow's tail without causing noticeable discomfort to the cow. The casing is a sealed casing and a rubber seal 33 is provided (as shown in Figure 12) to limit the possibility of there being ingress of dirt or moisture into the casing 3.

In use, the birthing sensor will be mounted on the tail 30 of the cow 32 in the manner described and as illustrated by Figures 13(a) to 13(c) inclusive, and the movements of the cow and in particular the movements of the cow's tail will be monitored by the birthing sensor 1. The three axes accelerometer 43 will detect the position of the cow's tail! preferably a plurality of times every second (for example, 4 times a second) and compare the movements and the position of the cows tail with impending birth movement indicators stored in microcontroller 41 memory. If the monitored movement patterns match one of the impending birth movement indicators stored in memory, an alert is sent to the responsible person.

The impending birth movement patterns will effectively comprise, for example, a set of rules which are used to determine whether or not the cow is in labour. The rules may be whether the tail has been in a raised configuration (as illustrated in Figures 16 and 17) for a predetermined period of time, whether the tail has been raised a predetermined number of times in a given time period, whether or not the cow has laid down a predetermined number of times in a time period, whether the cow has been lying down for longer or shorter than a predetermined time period, whether the cow's back is arched or a combination of two or more of the above conditions. The number of times that the cow raises their tail or lies down, and the time durations and predetermined time periods are preferably programmable into the microcontroller as these may vary from breed to breed as well as from species to species, and it may be preferable to program these appropriately to provide the optimum amount of time for the farmer or veterinarian to get to the animal in question.

It would appear that the tail angle and time tail raised product when measured with an accelerometer is not a highly reliable indicator of calving. However, it appears that the general large scale activity of the cow is much greater in the couple of hours leading up to calving. The activity patterns appear as though the cow is restless, repeatedly standing up and lying down, for example. In the days prior to labour there seems to be much smaller levels of gross movement. Preferably, the impending birth pattern will be a threshold energy value for a given time period, that if exceeded, will indicate that the animal is in labour. This will be described in more detail below.

Referring once again specifically to Figures 13(c) and 16, there are shown a plurality of axes marked x-x, y-y, and z-z respectively. The sensor is placed with the accelerometer's main axis aligned with the x-x axis so that the accelerometer will measure raising and lowering of the cow's tail (as shown raised in Figure 16 and lowered in Figure 13(c)). This will be referred to as the pitch movement of the tail. The y-y axis is the laterally arranged axis and will detect movements of the tail in this lateral axis.

Specifically, the y-y axis will detect when the tail is on its side for a prolonged period of time as would often be the case if the animal was lying down or whether it the tail is pointing downwards rather than to a side as would be the case if the animal were standing up. This y-y axis measurement will be referred to as the roll angle. Finally, the z-z axis is perpendicular to both the x-x and y-y axes and in Figure 13(c) is shown aligned longitudinally with respect to the animal and this is often referred to as the yaw angle. Note that the x-x, y-y and z-z axes are all referenced to the casing and the body on which the device is mounted rather than being referenced to earth. In the embodiment described below, only the pitch and the roll angles with respect to earth are monitored and calculated. The yaw angle cannot be calculated from accelerometer measurements. However the z-z axis of the accelerometer assures that the pitch and roll angles can be measured irrespective of the orientation of the sensor. In other instances, it may only be necessary to calculate either the pitch or the roll angle however the following example details a situation where both angles are captured.

In use, the sensor is used to detect the general large scale activity of the cow even though the sensor is placed on the tail of the animal. Various techniques are used, as will be described in greater detail below, to cancel out interference and irrelevant movements of the cow. The acceleration is detected in the relevant axes four times every second. According to the invention, it is important to measure the gross (slow) movement of the cow, or in particular, her change in position/posture rather than the fast movements, like swinging of the tail from side to side, raising of the tail for a bowel movement and the like. Therefore! according to the present invention, the acceleration data over a relatively long period is averaged to provide samples to a detection algorithm (which is used for matching of the sensed data with an impending birth indicator). Thus, the first step in the process is to average the acceleration samples obtained from the accelerometer over a time span of the range 15 to 60 seconds. In the present example, the acceleration samples are averaged over a period of 15 seconds. The accelerations samples are averaged by summing all the acceleration samples together. This has the effect of averaging out any actual sudden movements of the cow, and leaves the orientation of the cow intact. In other words, the gravity component, or the acceleration due to gravity in the x-x, y-y and z-z axes, which is an indication of the orientation of the cows tail, is obtained. Thus swishing of the tail, vibrations and other movements are filtered at this stage, whereas the pitch and roll of the sensor remain the piinciple component of the averaged signal.

Once the signal has been averaged, it is then necessary to calculate the energy in the change in the cow's position. In particular, it is necessary to calculate the energy in the change in the cow's tail's pitch and roll. Once that has been calculated, the energy value can be compared to a threshold energy value and if the energy value of the tail is higher than the threshold energy value, then it can be assumed that the cow is in labour. The precise steps will be described in further detail below: First of all, the acceleration samples are added together and averaged over a first time period, for example 15 seconds. The pitch and roll angles are then calculated for each averaged acceleration sample. The pitch angle is calculated according to the formula: Pitch angle = Tan (x I [{y2 +z2}1]) The roll angle is calculated according to the formula: Roll angle = Tan1 (y / [{x2 +z2}]) The above equations are used when three axes are monitored. If only two axes are monitored, the following equations could be used. The pitch angle could be calculated according to the formula: Theta = asin(Ax) Where theta is the angle that the accelerometer makes with level ground and Ax is the measured acceleration by the accelerometer in the x-x axis direction in units of g. The roll angle could be calculated according to the formula: Theta = asin(Ay) Where theta is the angle that the accelerometer makes with level ground and Ay is the measured acceleration by the accelerometer in the y-y axis direction in units of g.

Once the angles are determined, a high pass filter (HPF) is applied to the pitch and roll angles. This is achieved by, for example, passing the pitch and roll angles through a differentiator in order to obtain the difference of the current pitch and roll angles with the previous pitch and roll angles.

Then, once the first derivative has been obtained, the magnitude of the resulting pitch and roll signals are obtained by obtaining the modulus of the resulting signals and these signals are summed. Finally the moduli of the resultant signals are summed, or more specifically, integrated over a detection window length which may be set at the outset of the device's operation. For example, the detection window length may be 15 minutes in duration. Therefore, for each 15 second time increment, the integration of the summed moduli of signals is compared to the threshold.

The integration of the pitch moduli of signals may be compared to a pitch threshold and/or the integration of the roll moduli of signals may be compared to a roll threshold and either or both of these may be used to determine whether or not the animal is in labour. Alternatively, both the integration of the pitch moduli of signals and the integration of the roll moduli of signals may be combined together and compared against a combined threshold value.

In order to implement the high pass filter (HPF) and obtain the first derivative of the pitch and roll signals, a long time constant is not required or indeed useful. It is possible to simply compare each new sample with the last sample and calculate it as follows: ds/dt = (s_new-s_old so in this case, the t is 1 time period (60 samples 115 seconds).

The two resulting outputs of the algorithm are the 1) Pitch energy value (a figure of the variation in pitch angle of the sensor over a time window of about 10 to 15 minutes) and the 2) Roll energy value (a figure of the variation in roll angle of the sensor over a time window of about 10 to 15 minutes). At present, there is insufficient data captured to know precisely what the calving threshold values should be set to for each of these signals, but in due course that will become clear once many data sets are captured and analyzed. It is quite likely that only one of pitch or roll may be required for reliable calving detection, or that the sum of both is enough to compare to a single threshold value.

According to one implementation of the present invention, the two outputs, namely the pitch energy value and the roll energy value are output as a pair of positive numerical values for each time window and a determination is made based on the pair of numerical values whether or not the animal is in labour. The numerical values range from zero to up to approximately 30 and once it is found that one or both of the pitch energy value and or the roll energy value has a value of greater than or equal to 20 for three or more consecutive time windows, it is determined that the animal is in labour. This is simply illustrative of the current operation of one implementation of the invention and other criteria may be used instead depending on the animal and the analysis of monitored data in order to make the method more accurate.

Referring specifically to Figure 17, there is shown a diagrammatic representation of one system in which the method according to the present invention may be implemented.

The birthing sensor has an algorithm that compares the measured tilt angle of the cow's tail 30 with respect to level ground with a configurable reference tilt angle. If the birthing sensor detects that the tilt of the cows tail is above the reference tilt angle for a configurable number of seconds, (in other words, it matches an impending birth movement pattern stored in memory), the birthing sensor will determine that the cow is in labour. An SMS message is sent from the wireless communication module (not shown) in the birthing sensor 1 to an antenna 51 of a GSM network. The antenna will relay the SMS message to the mobile telephone 61 of the farmer or the veterinarian alerting them to the fact that the cow is in labour and that delivery is imminent. The farmer or veterinarian can then make their way to the animal in question to assist in the delivery of the calf. For simplicity, the remaining parts of the GSM network including other antennae, the base station controllers, the mobile switching centre and the like have been omitted from the drawing. However, it will be understood that these parts would also be present in the GSM network however their inclusion in this description is not essential to the understanding of the present invention.

It is envisaged that various modifications could be made to the embodiment shown in the drawings without departing from the spirit of the present invention. For example, instead of providing a single channel-shaped flange than extends substantially the entire length of the casing 3, a smaller flange that extends only part of the length of the casing could be provided, a plurality of channel shaped flanges could be provided and indeed, one or more hooks for receiving the resiliently deformable continuous securing strap could be provided instead of a channel shaped flange. In addition to the above, padding such as a sponge or other resiliently deformable material could be placed on the bottom of the casing to provide a cushion layer between the casing and the tail of the cow. A non-slip coating that preferably is non-abrasive to the animal, can also be placed directly onto the bottom of the casing or onto the padding layer, if one is provided, in a location on the padding layer where it comes into contact with the animals tail.

Instead of a microcontroller, a controller and memory could be provided in its stead. The controller or microcontroller if appropriate may be pie-programmed or programmable.

The communications between the birthing sensor and the farmer/veterinarian are preferably via SMS over a GSM network however other configurations for data communications are possible and readily envisaged. It is envisaged that the birthing sensor may support two way communications so that the birthing sensor can also receive requests for information or commands via SMS or other means through the wireless communication network. A command may be transmitted to the device, such as a number to send an alert notification to in the event of an animal going into labour, the parameter(s) of any of the impending birth movement patterns stored in memory, or for the device to wake up or go into hibernation.

In the embodiment shown, the processing is carried out on the microcontroller on the birthing sensor however if desired, the birthing sensor can simply transmit the sensed data onwards to a remote third party location where the data can be analysed and thereafter a notification can be sent by the third party to the farmer or the veterinarian. In large herds, it may be desirable to provide a unique identifier as part of the alert message that will indicate which cow or heifer is going into labour. Finally, although the present invention has been described in terms of cows and heifers, it is envisaged that the present invention could also be used with other species of animal.

In addition to the above, it is envisaged that the device may be provided with a GPS component that will allow the location of the device, and by extension the location of an animal wearing the device, to be provided to the responsible person. This will allow the responsible person to locate the animal with ease. Furthermore, the device may be provided with one or more temperature sensors. For example, the device may be provided with a temperature sensor suitably positioned to monitor the ambient temperature of the air in the vicinity of the animal. In addition to or instead of the ambient temperature sensor, there may be provided a temperature sensor in a position adjacent to the animal's tail to monitor the temperature of the animal. If the temperature of the animal is monitored, this may provide useful information regarding the state of wellbeing of the animal.

In this specification the terms "comprise, comprises, comprised and comprising" and the terms include, includes, included and including" are all deemed totally interchangeable and should be afforded the widest possible interpretation.

The invention is in no way limited to the embodiments hereinbefore described but may be varied in both construction and detail within the scope of the claims.