INTRODUCTION
A monitor system is described which is capable of providing an output which indicates the oscillatory torque in each section of a multi-section shaft of a rotating system having plural masses. The system described is an electronic model of a mathematical analog of the rotating system and is based upon the assumption that the system may be represented as N inertias or masses interconnected by N-1 shafts -- represented as springs. For such a system there are n-1 primary frequency oscillatory torques. If the inertias are large, the frequencies of these torques are low. Electrical signals representing the torques are sensed at one or more shaft sections and are filtered, amplified, passed through a plurality of weighting network and recombined to provide an indication of the total oscillatory torque in each of the N-1 shaft sections. Such torque, or an electrical output signal from a generator, in the instance of a turbine-generator set may be used to actuate an operative means or actuate a system alarm. A torque sensor based on the Villari effect. The sensor uses high frequency alternating magnetic fields and the Villari effect to determine the state of stress/strain inside a magnetostrictive shaft for the purpose of measuring torque. The invention teaches design elements for the sensor and shaft; namely, the desirable magnetic, electric and structural properties for various elements of the sensor.
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ELECTRIC MOTORS |
An electric motor is a motor that uses electrical energy to produce mechanical energy, usually through the interaction of magnetic fields and current-carrying conductors. The reverse process, producing electrical energy from mechanical energy, is accomplished by a generator or dynamo. Traction motors used on vehicles often perform both tasks. Electric motors can be run as generators and vice versa, although this is not always practical. Electric motors are ubiquitous, being found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives. They may be powered by direct current (for example a battery powered portable device or motor vehicle), or by alternating current from a central electrical distribution grid. The smallest motors may be found in electric wristwatches. Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses. The very largest electric motors are used for propulsion of large ships, and for such purposes as pipeline compressors, with ratings in the millions of watts. Electric motors may be classified by the source of electric power, by their internal construction, and by their application.
PHYSICAL PRINCIPAL
The physical principle of production of mechanical force by the interactions of an electric current and a magnetic field was known as early as 1821. Electric motors of increasing efficiency were constructed throughout the 19th century, but commercial exploitation of electric motors on a large scale required efficient electrical generators and electrical distribution networks.
Comparison of motor types
| Type | Advantages | Disadvantages | Typical Application | Typical Drive |
| Least expensive | Rotation slips from frequency | Fans | Uni/Poly-phase AC | |
| High power | Rotation slips from frequency | Appliances | Uni/Poly-phase AC | |
| Rotation in-sync with freq | More expensive | Industrial motors | Uni/Poly-phase AC | |
| Precision positioning | Requires a controller | Positioning in printers and floppy drives | ||
| Long lifespan | High initial cost | Hard drives | Multiphase DC | |
| Low initial cost | High maintenance (brushes) | Treadmill exercisers | Direct PWM | |
| - | - | - | - | |
| - | - | - | - | |
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Torque motors
A torque motor (also known as a limited torque motor) is a specialized form of induction motor which is capable of operating indefinitely while stalled, that is, with the rotor blocked from turning, without incurring damage. In this mode of operation, the motor will apply a steady torque to the load.
A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively-constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches. In the computer gaming world, torque motors are used in force feedback steering wheels.
Another common application is the control of the throttle of an internal combustion engine in conjunction with an electronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
Torque capability of motor types
When optimally designed for a given active current (i.e., torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and core flux density, all categories of electric motors or generators will exhibit virtually the same maximum continuous shaft torque (i.e., operating torque) within a given physical size of electromagnetic core. Some applications require bursts of torque beyond the maximum operating torque, such as short bursts of torque to accelerate an electric vehicle from standstill. Always limited by magnetic core saturation or safe operating temperature rise and voltage, the capacity for torque bursts beyond the maximum operating torque differs significantly between categories of electric motors or generators.
Electric machines without a transformer circuit topology, such as Field-Wound (i.e., electromagnet) or Permanent Magnet (PM) Synchronous electric machines cannot realize bursts of torque higher than the maximum designed torque without saturating the magnetic core and rendering any increase in current as useless. Furthermore, the permanent magnet assembly of PM synchronous electric machines can be irreparably damaged, if bursts of torque exceeding the maximum operating torque rating are attempted.
Electric machines with a transformer circuit topology, such as Induction (i.e., asynchronous) electric machines, Induction Doubly-Fed electric machines, and Induction or Synchronous Wound-Rotor Doubly-Fed (WRDF) electric machines, exhibit very high bursts of torque because the active current induced on either side of the transformer oppose each other and as a result, the active current contributes nothing to the transformer coupled magnetic core flux density, which would otherwise lead to core saturation.
Electric machines that rely on Induction or Asynchronous principles short-circuit one port of the transformer circuit and as a result, the reactive impedance of the transformer circuit becomes dominant as slip increases, which limits the magnitude of active (i.e., real) current. Still, bursts of torque that are two to three times higher than the maximum design torque are realizable.
The Synchronous WRDF electric machine is the only electric machine with a truly dual ported transformer circuit topology (i.e., both ports independently excited with no short-circuited port). The dual ported transformer circuit topology is known to be unstable and requires a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set. If a precision means were available to instantaneously control torque angle and slip for synchronous operation during motoring or generating while simultaneously providing brushless power to the rotor winding set the active current of the Synchronous WRDF electric machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable. Torque bursts greater than eight times operating torque have been calculated.
OBJECTIVES
The objective of this study is to identify the best indexed position of two rotating groups within a tandem axial-piston pump for attenuating the torque ripple amplitude that is exerted on the shaft. By attenuating the torque ripple characteristics of the pump, other vibration aspects of the machine are also expected to be reduced. In particular, the objectives of this paper are aimed at reducing the noise that is generated by the pump. This paper begins by considering the theoretical torque ripple that is created by the discrete pumping elements of a single rotating group within an axial piston machine. From this analysis, an equation is produced that describes a single pulse for the torque ripple as a function of the average torque and the total number of pistons that are used within the rotating group. By superposing another rotating group on top of the first, and by indexing the angular position of one rotating group relative to the other, a second equation is produced for describing the theoretical torque ripple of a tandem pump design. This equation is also a function of the average shaft torque and the total number of pistons that are used within a single rotating group; however, an additional parameter known as the index angle also appears in this result. This index angle is shown to amplify or attenuate the amplitude of the torque ripple depending upon its value. From these results, it is shown that a proper selection of the index angle can reduce the torque ripple amplitude by as much as 75%.
Torque - expressed in degrees, this measurement explains the shafts resistance to twisting when a force is applied. The lower the torque rating, the more resistant the shaft is to twisting. Steel golf shafts have such low torque values (high resistance to twisting) that True Temper does not publish steel torque ratings. However, all graphite / composite shafts will have established torque values.
Balance point – the point along the length of the shaft at which it will balance itself when placed on a fulcrum.
Swingweight – the method by which the balance point of a finished golf club is expressed. It represents the relationship of weight distribution between the head and the grip of the golf club. It does not represent overall weight. Two clubs with identical overall weights could have substantially different swingweights leading to varying performance
Parallel shafts – shafts that have the same diameter for a specific length up from the tip. Generally, wood shafts will have either a .335” or .350” parallel section and parallel irons will have a .370” diameter.
Taper tip shafts – shafts that have larger diameters out from the tip end. Today, taper tip shafts are solely for irons and have a .355” diameter at the tip. The benefit to taper tip shafts is that each shaft throughout the set is specifically designed for a corresponding head (i.e., 5-iron, 6-iron, etc.) resulting in unmatched consistency and performance.
Discrete length – shafts that are manufactured specifically for each respective iron head. Discrete length shafts generally are taper tipped and found in lengths from 41” (1-iron) to 37” (9 iron & wedges). True Temper does offer a parallel tip, discrete length product in Tri-Gold®.
Step up – this process can only be done with tapered tip product and will weaken the overall flex of the shaft by a sub-flex. It is accomplished by taking the 2 iron shaft and placing it in the 3 iron head and continuing this trend throughout the set. By doing this, you will increase the length to 1st step measurement by 1/2".
Step down – this process can only be done with tapered tip product and will strengthen the overall flex of the shaft by a sub-flex. It is accomplished by taking the 3 iron shaft and placing it in the 2 iron head and continuing this trend throughout the set. By doing this, you will decrease the length to 1st step measurement by 1/2".
Step down – this process can only be done with tapered tip product and will strengthen the overall flex of the shaft by a sub-flex. It is accomplished by taking the 3 iron shaft and placing it in the 2 iron head and continuing this trend throughout the set. By doing this, you will decrease the length to 1st step measurement by 1/2”.
Unitized shafts – shafts that are manufactured to a single, raw length (always parallel tip) and then tip and butt trimmed in increments to achieve proper step pattern and flex pro
Bolted joint
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Bolted joint |
Screw joint |
Stud joint |
Bolted joints are one of the most common elements in construction and machine design. They consist of cap screws or studs that capture and join other parts, and are secured with the mating of screw threads.
There are two main types of bolted joint designs. In one method the bolt is tightened to a calculated clamp load, usually by applying a measured torque load. The joint will be designed such that the clamp load is never overcome by the forces acting on the joint (and therefore the joined parts see no relative motion).
The other type of bolted joint does not have a designed clamp load but relies on the shear strength of the bolt shaft. This may include clevis linkages, joints that can move, and joints that rely on locking mechanism (like lock washers, thread adhesives, and lock nuts).
A spring bolt is a bolt which must be pulled back and which is brought back into place by the spring when the pressure is released. Spring bolts are used in Rubik's Snakes, for example, the wedges of which are pulled apart slightly when twisted and are pulled back together by the spring bolt when shifted back into position.
Setting the torque
§ Engineered joints require the torque to be accurately set. Setting the torque for cap screws is commonly achieved using a torque wrench. The required torque value for a particular screw application may be quoted in the published standard document or defined by the manufacturer.
§ The clamp load produced during tightening is higher than 75% of the fastener's proof load. To achieve the benefits of the pre-loading, the clamping force in the screw must be higher than the joint separation load. For some joints a number of screws are required to secure the joint, these are all hand tightened before the final torque is applied to ensure an even joint seating.
§ The torque value is dependent on the friction between the threads and beneath the bolt or nut head, this friction can be affected by the application of a lubricant or any plating (e.g. cadmium or zinc) applied to the screw threads. The screw standard will define whether the torque value is for a dry or lubricated screw thread. If a screw is torqued rather than the nut then the torque value should be increased to compensate for the additional friction - screws should only be torqued if they are fitted in clearance holes.
§ Lubrication can reduce the torque value by 15 – 25%, so lubricating a screw designed to be torqued dry could over tighten it. Over tightening may cause the bolt to fail, it could damage the screw thread or stretch the bolt. A bolt stretched beyond its elastic limit may no longer adequately clamp the joint.
§ Torque wrenches do not give a direct measurement of the clamping force in the screw - much of the force applied is lost in overcoming friction. Factors affecting the tightening friction: dirt, surface finish, lubrication, etc. can result in a deviation in the clamping force.
§ More accurate methods for setting the screw clamping force rely on defining or measuring the bolt extension. The screw extension can be defined by measuring the angular rotation of the screw (turn of the nut method) which gives a screw extension based on thread pitch. Measuring the screw extension directly allows the clamping force to be very accurately calculated. This can be achieved using a dial test indicator, reading deflection at the bolt tail, using a strain gauge or ultrasonic length measurement.
§ There is no simple method to measure the tension of a bolt already in place other than to tighten it and identify at which point the bolt starts moving. This is known as re-torqueing. An electronic torque wrench is used on the bolt under test, and the torque applied is constantly measured. When the bolt starts moving (tightening) the torque briefly drops sharply - this drop-off point is considered the measure of tension.
§ Recent developments enable bolt tensions to be estimated by using ultrasonic testing. Another way to ensure correct bolt tension (mainly in steel erecting) involves the use of crush-washers. These are washers that have been drilled and filled with orange RTV. When the orange rubber strands appear, the tension is correct.
§ Large volume users such as auto makers frequently use computer controlled nut drivers. With such machines the computer in effect plots a graph of the torque exerted. Once the torque reaches a set maximum torque chosen by the designer, the machine stops. Such machines are often used to fit wheelnuts and will normally tighten all the wheel nuts simultaneously.
Measurement of frictional torque of threads in bolt
The torque is applied by means of suspending the weights on one end of the rope and other end is wound around the head of the bolt and tied to the projection. The amount of load is increased gradually till the bolt starts rotating. The applied load is then calculated by adding up the weights. This is the load that is required to overcome the friction between the threads. Similarly the net applied torque is calculated by multiplying the resultant load by bolt head radius.
In another method the torque is applied to the nut by an electromagnetic force. A specially designed gripper is used to grip the nut. A bar magnet is mounted on two sides of the gripper. Externally a coil is wound in which AC (alternating current) current is passed. As the magnetic field from the permanent magnet interacts with the field created by the coil, a torque is generated which would try to rotate the magnet, thus rotating the nut. This is quite similar to the construction of the motor, and hence a motor can be directly used to provide the torque. Stepper motor can be used so that the torque is provided in steps, as desired, each time giving a small angular displacement. The torque provided by the motor can be known at each discrete angular displacement of Δθ. The process is repeated until the nut has traversed to the desired length of the bolt. The discrete torques can be added to get the net torque consumed in displacing the nut from one end of the bolt to the desirable point. This is the torque that is required to overcome the friction between the threads.
RESULT
The results of a finite element analysis of a trilobe polygon shaft connection used as an alternative for a spline for torque transmission is presented. These results are compared to the results of a finite element analysis previously performed on an involute spline. It is shown that the tensile stress in the polygon shaft is significantly smaller than in the involute spline and is smaller than all the other stresses in both the shaft and the hub in the polygon connection. Furthermore, the magnitudes and distributions of the maximum principal compressive stress, the shear stress, and the Von Mises stress are nearly the same on the shaft and the hub. It appears that polygonal connections can be more advantageous than splined connections because of lower stresses and the lack of stress concentrations typical of splines
Applying a magnetic field causes stress that changes the physical properties of a magnetostrictive material. The reverse is also true: applying stress to a magnetostrictive material changes its magnetic properties (e.g., magnetic permeability). This is called the Villari effect.
The inventions described and/or claimed herein relate to novel torque sensor topologies that use high frequency alternating magnetic fields and the Villari effect to determine the state of stress/strain inside a shaft made of a magnetostrictive material for the purpose of measuring torque. The inventions relate to various design elements for the sensor and shaft including but not limited to desirable magnetic, electric and structural properties for various elements of the sensor.
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