Piston-driven pneumatic step motor

Abstract

Pneumatic stepper motors provide a magnetic resonance (MR)-safe motor for use in the MR-environment. A pneumatic stepper motor of the present invention includes diaphragms or pistons for driving the motor. The pistons of the present invention are specially designed in order to make the overall device simpler and smaller. The pistons also increase the reliability of an already reliable motor design. The pneumatic stepper motor of the present invention can be manufactured entirely using three-dimensional printing or other additive manufacturing methods.

Description

PISTON-DRIVEN PNEUMATIC STEP MOTORCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U S. Provisional Application No. 63 / 724,082, filed November 22, 2024. The content of the aforementioned application is herein incorporated by reference, in its entirety.FIELD OF THE INVENTION

[0002] The present invention relates generally to stepper motors. More particularly, the present invention relates to a diaphragm or piston-driven pneumatic step motor.BACKGROUND OF THE INVENTION

[0003] Among medical imaging modalities, Magnetic Resonance (MR) provides the most detailed soft tissue visualization. Additional demand is derived from its non-ionizing radiation that it is unknown to damage the body, for example in pediatric imaging. Due to spatial constrains of the scanner, extending these capabilities from diagnosis to direct (in scanner) MR-guided interventions often requires specialized remote manipulation devices / robots. Compatibility of mechatronic technology with the MR environment, however, is highly demanding due to physical interaction with the large magnetic fields and interference with the feeble radio waves that capture the image, raising saf ety and efficacy concerns, respectively. The Food and Drug Administration (FDA) recognizes the American Society for Testing and Materials (ASTM) consensus standard F2503 to classify devices for the MR environment. At the highest compatibility level are MR Safe devices, which pose no known hazards resulting from exposure to any MR environment. MR safe devices also operate accurately and safely in the MR environment without interfering with the functionality of the imager.

[0004] Demand for MR-Safe robots gained additional traction with the recent developments of helium-free scanners. These have lower field strength but are less expensive, portable, smaller, more ergonomic, and target in-office interventions. The addition of robots adds precision for therapy delivery and promises physician-skill-independent clinical performance. The magnetic field is lower but so is the magnitude of the imaging waves, making MR-safe devices timelier than ever.

[0005] Numerous MR conditional and MR-safe motors and robots have been developed over the last two decades, including piezoelectric, hydraulic, and pneumatic actuation. Here, the focus is pneumatic motors, servo, or stepper-types,

[0006] A servo-type motor commonly uses two air lines that are pressurized differentially by one or two remotely located proportional control valves. The motion / position of the motor is controlled servo pneumatically with feedback from a sensor. The simplest approach is a pneumatic cylinder and the output is linear. Turbine / vane type motors have been used for rotary motion. These work best at high speed and commonly require gearheads Power is typically high, through speed. However, cylinders capture the static pneumatic pressure while turbines harvest the dynamic pressure. Static position control of the motor is difficult. As such, a recent design devised a vane type turbine to capture part of the static pressure. The power performance was outstanding. Another approach to seal the rotor was to use cycloidal shaped rotors, but sealing remained difficult, as with Wankel engines. Commonly, servo pneumatic control for accurate position is difficult due to the compressibility of air. For MR!, the driving valves should clear the 05 mTesla (5 Gauss) line and so the hoses are typically long, over 4m. The length of the hoses increases response times. For example, for accurate position control hoses were limited to 0.5m and did not consider the impact of the long transmission hoses. Overall, long hoses are necessary for the MR environment making servopneumatic motors evermore difficult to control. They are well suited for high power applications where accurate position control is not a requirement. Torque and speed are not influenced by the length of the hoses.

[0007] The other approach for MRI motors is stepping. Step motors are connected with 3 or more air hoses driven by on-off valves. Air pulses sent by the valves are converted to mechanical steps, and so position control is trivial, pulse-to-step. Position errors are bounded by the step size and noncumulative, unless steps are skipped. Open loop control works, but encoders are normally used to account for skipping, especially in medical use.

[0008] The first pneumatic step motor was built entirely of MR-safe materials. Several step motors have been reported since, using crank, wedge, and rack-pinion mechanisms. Crank mechanism motors connect a piston / diaphragm to a crank. like many engines. The number of steps per turn is normally double the number of pistons, so steps are large, and gearheads are typically used to reduce the step size. An original feature of the original pneumatic step motor, which is also a crank type motor, was that the gearhead was integrated with the crank mechanism (hoop gear).

[0009] Wedge type steppers use pistons that push'pull a wedge into a gear / rack like output element. Several types have been presented, including one that can do rotary or translational motion Several are MR-safe and have shown good accuracy. The weakest components are the wedges, their sliding friction making them wear prone. Most recently, a new stepper approach devised a way to eliminate sliding with 4 pistons that push 4 racks about a central gear.

[0010] Commonly for steppers, long hoses act as a low-pass filter on the pressure pulse waves thus limiting speed. Overall, steppers are good precision motors, but speed is limited by the length of the hoses.

[0011] It would therefore be advantageous to provide a new, improved design for pneumatic stepper motors.SUMMARY OF THE INVENTION

[0012] The foregoing needs are met, to a great extent, by the present invention, wherein one aspect is a. motor having a hoop gear and an output gear. The hoop gear and the output gear have teeth having an involute, shifted geometry. The motor also includes a driving mechanism. The driving mechanism is configured to engage the hoop gear and the hoop gear in turn engages the output gear.

[0013] In accordance with an aspect of the present invention, the driving mechanism is a diaphragm. The driving mechanism is a piston, and the piston has a barrel shape, in some embodiments. The piston is directly connected to a crankshaft for the hoop gear. The driving mechanism can be engaged with air. In some embodiments, the air is passed through an air vent. The motor can include a three-channel encoder. The motor is MR-Safe.

[0014] In accordance with another aspect of the present invention, a pneumatic motor includes pistons, wherein the pistons are connected directly to a crank shaft. The pistons are barrel shaped. The driving mechanism is engaged with air. Calibrated air vents in close proximity of the cylinder allow a small amount of air to escape.

[0015] In accordance with an aspect of the present invention, a pneumatic motor includes pistons. The motor includes a crank shaft. The pistons are connected directly to the crank shaft.

[0016] In accordance with another aspect of the present invention, the pistons are barrel shaped.

[0017] In accordance with another aspect of the present invention, a device for actuating a target component of a motor includes an air-driven driving mechanism. The air-driven driving mechanism is pressurized by air, which then causes the air-driven driving mechanism to actuate the target component of the motor.

[0018] In accordance with another aspect of the present invention, the air-driven driving mechanism includes a diaphragm. Alternately, the air-driven driving mechanism comprises a piston. The piston can have a barrel shape. The piston is directly connected to a crankshaft for the motor. The device includes calibrated air vents configured to allow a small amount of air to escape. The device includes a three-channel encoder. The device for actuating a target component of the motor is MR-Safe.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings provide visual representations, which will be used to more fully describe the representative embodiments disclosed herein and can be used by those skilled in the art to better understand them and their inherent advantages. In these drawings, like reference numerals identify corresponding elements and:

[0020] FIGS. 1 A and IB illustrate diaphragm and piston versions of a pneumatic stepper motor, according to embodiments of the present invention.

[0021] FIG. 2A illustrates an exploded view of a pneumatic stepper motor having pistons, according to an embodiment of the present invention.

[0022] FIG. 2B illustrates a graphical view of steps of the piston-driven pneumatic stepper motor shown in FIG. 2A

[0023] FIGS. 3A and 3B illustrate perspective views of a diaphragm based and a piston- driven pneumatic stepper motor, respectively, according to an embodiment of the present invention.

[0024] FIG. 4A illustrates a motor test stand, and FIG. 4B illustrates an image view of a testing setup for motors according to an embodiment of the present invention

[0025] FIG. 5 illustrates a schematic diagram of a variable area flowmeter.

[0026] FIGS. 6A and 6B illustrate graphical views of torque, power and air consumption versus speed with 4.5 m long hoses for the PneuStep-D and the PneuStep-P, respectively.

[0027] FIG. 7 illustrates graphical views of torque, power and air consumption versus speed at hose lengths of 0.5 m to 4.5 m long hoses for the PneuStep-D and the PneuStep-P, respectively.

[0028] FIG. 8 illustrates a graphical view of a PneuStep-P angular position error from step center and endurance-test.DETAILED DESCRIPTION

[0029] The presently disclosed subject matter now will be described more fully hereinafter with reference to the accompanying Drawings, in which some, but not all embodiments of the inventions are shown. Like numbers refer to like elements throughout. The presently disclosed subject matter may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Indeed, many modifications and other embodiments of the presently disclosed subject matter set forth herein will come to mind to one skilled in the art to which the presently disclosed subject matter pertains having the benefit of the teachings presented in the foregoing descriptions and the associated Drawings. Therefore, it is to be understood that the presently disclosed subjectmatter is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

[0030] Pneumatic stepper motors provide a magnetic resonance (MR)-safe motor for use in the MR-environment. A pneumatic stepper motor of the present invention includes pistons for driving the motor. The pistons of the present invention are specially designed in order to make the overall device simpler and smaller The pistons also increase the reliability of an already reliable motor design. The pneumatic stepper motor of the present invention can be manufactured entirely using three-dimensional printing or other additive manufacturing methods.

[0031] Magnetic Resonance Imaging (MRI) is capable of the clearest soft tissue imaging for diagnosis Using medical devices within the MRI scanner extends the capability to MRI- guided interventions. However, device compatibility with the MR environment is highly demanding, especially for active devices. The first fully MRI compatible motor, a Pneumatic Step Motor (PneuStep), was developed in 2008. According to the Food and Drug Administration (FDA) recognized consensus standard ASTM F2503, the PneuStep is an MR-safe component. Several other MR-safe motors have been reported since. The PneuStep was used to drive various clinical MR-safe robots, was highly cited, and licensed to several companies.

[0032] In 2008, subtractive manufacturing was used to build the PneuStep. Since then, additive manufacturing progress has enabled the update and improvement of the design for rapid prototyping. The present invention is directed to a fully 3D printed PneuStep motor, that is referred to herein as PneuStepl. As with PneuStep, the active elements of PneuStepl are pneumatic rolling diaphragms. These were the weakest components of the motor.Therefore, the present invention is also directed to a novel design variation that replaces thediaphragms with pneumatic pistons, called PneuSteplP. This is a substantial improvement for reliability that is also simpler and more performant, as will be demonstrated further herein.

[0033] Two new designs are shown here, side by side, along with images of their prototypes, and comparative assessment. Within the same overall motor size, the piston version of the pneumatic stepper motor increased the cylinder capacity from 0.4cm3to 0.897cm3. Compared to the same size original PneuSlep, the updated versions reduced the step size from 4° to 2.5°.

[0034] One embodiment of a pneumatic stepper motor of the present invention includes improved gearing and refined for additive manufacturing and is referred to herein as PneuStepl. It continues to use diaphragms as driving elements. Another embodiment of the present invention uses pistons instead and is referred to herein PneuSteplP. This also simplifies the design and improves performance. An original optic fiber encoder is also presented.

[0035] FIGS. 1A and IB illustrate diaphragm and piston versions of a pneumatic stepper motor, according to embodiments of the present invention. FIG 1 A shows the PneuStepl design, with diaphragms. The body size is the same as the original diaphragm driven PneuStep, 70mm outer diameter and 25mm thickness. In short, the diaphragms sequentially pressurize through the air ports act on the hoop part that spins the cranks of the 3-parallelogram mechanism (3P). At the level of the cranks the step size is large (360° / 3 ports / 2 half-step::::60°). A built-in gearhead consisting of the inner gear of the hoop and outer output gear reduces the size of the step and increases torque. The arm of the cranks must equal the distance between the axes of the gears. A challenging problem of the motor design is to increase the gear transmission ratio while maximizing the arms of the cranks without causing interference between the teeth of the gears. Here, the entire mechanism wasresized / redesigned. The teeth of the internal and external gears have involute shifted profile with module 1mm, pressure angle 20°, number of gear teeth Zg=24 and hoop teeth Zh=25.

[0036] The transmission ratio T=Zg / (Zh-Zg)=24, and so the step size of the cranks is reduced to 60 / 24=2.5°. PneuStepl also includes several design refinements for stereolithography 3D printing, such as cavitation releases. Moreover, the motor output is either rotary if connecting to the output shaft, or translational if a screw is used to engage the nut within the output gear (currently 4.5mm pitch, 3 starts resulting in 0.03125mm steps). The screw is not shown, for brevity

[0037] FIG. 1 A illustrates a motor 10 driven by a driving mechanism taking the form of diaphragms 12. The diaphragms 12 are secured by mounting hardware 14 and are engaged by air driven through air ports 16. The diaphragms 12 are sequentially pressurized by air passing through the air ports 16 to in turn act on the hoop gear 18 that spins the cranks 20 of the 3-parallelogram mechanism (3P). A built-in gearhead consisting of tire inner gear of the hoop gear 18 and outer output gear 24 reduces the size of the step and increases torque The arm of the cranks 20 must equal the distance betw een the axes of the gears. The teeth of the hoop gear 18 and the output gear 24 have involute shifted profile with module 1mm, pressure angle 20°, number of gear teeth Zg==24 and hoop teeth Zh::::25.

[0038] FIG. IB illustrates a variation on the pneumatic stepper motor with pistons instead of diaphragms. The motor 10 includes pistons 26. Like the diaphragms of the embodiment of FIG. 1 A the pistons 26 are actuated wath air that flows through air ports 16. The pistons 16 then are sequentially pressurized by air passing through the air ports 16 to in turn act on the hoop gear 18 that spins the cranks 20 of the 3-parallelogram mechanism (3P). The pistons 26 are directly connected to the hoop gear 18 with pin 28.

[0039] The pistons 26 have special kinematics and design. A typical piston translates within its cylinder and links to the crank with a connecting rod. For simplicity and size, the rod waseliminated, connecting the piston directly to the crank, which in the case of the present invention, is the hoop gear, as shown in FIG. IB and FIG. 2A. However, connecting directly changes the kinematics in that the piston will also tilt (piston pin moves on the crank circle, center point of piston head translates, so piston body translates and tilts), as shown in the supplement movies. To enable tilting, the piston needs a special design. The piston head has a barrel shape and uses a soft and compressed O-ring to seal throughout the stroke, including when the piston-cylinder contact region is elliptical in shape due to the tilting, as illustrated in FIG. 1B.

[0040] The pin is press-fit within the hoop gear and has a sliding fit into the piston Access holes and caps are made within the body to facilitate mounting the pin. Air within the cylinder is routed to the pin through a central channel to cool and lubricate the joint and reduce reciprocating mass. Optional small holes within the cylinders provide additional air vents, should this be needed for cooling.

[0041] Comparing FIGS 1 A and IB, shows that the piston version is significantly simpler by eliminating the diaphragm mounting hardware Moreover, the body no longer needs flat surfaces to mount the diaphragms and is entirely circular, making additional room to increase cylinder volume.

[0042] FIG. 2A illustrates an exploded view of a pneumatic stepper motor having pistons, according to an embodiment of the present invention. FIG. 2B illustrates a graphical view of steps of the piston-driven pneumatic stepper motor shown in FIG. 2A. The piston version of the pneumatic stepper motor has the same body size and uses the same gearing. However, the diaphragms were replaced with pistons 26, directly connected to the hoop gear with a pin 28, as shown in FIG. IB and in the exploded view shown in FIG. 2A. Atypical piston-crank connection uses a connecting rod and the piston translates. Eliminating the rod is simpler and smaller, but the piston 26 will include a rotational motion component (the piston head centertranslates, and the piston pin moves on a circle). As such, the piston head was made of a barrel shape and uses a compressed rubber O-ring 34 to seal throughout the stroke, on an ellipse when the piston tilts, element E in FIG. 1B.

[0043] The pin 28 is press-fitted within the hoop gear 18 and has a sliding fit into the piston 26. Access holes and caps are made within the body to facilitate mounting the pin. Air within the cylinder is routed to the pin 28 through a central channel, to cool and lubricate the joint. It also reduces reciprocating mass. Optional small calibrated / adjustable holes within the cylinders provide additional air vents, should this be needed for cooling. Comparing FIGS.1A and IB, show that the piston version is also significantly simpler eliminating the diaphragm mounting hardware. Moreover, the body 36 no longer needs flat surfaces to mount the diaphragms, is entirely circular, and has more room for the cylinders.

[0044] The encoder 30 of the motor was also updated from the original PneuStep, which used a transmissive quadrature incremental encoder (2-channels) implemented with optic fibers. Here, a 3-channel reflective type is used. The encoder 30 is only shown with the piston version, but is applicable to both designs. A codewheel of a semicircular shape (I count) is built within one of the crank shafts, as illustrated in FIG. 2A. Three transmitter-receiver optic fiber pairs 32 are mounted 120° apart within an encoder body. The beams of each pair intersect at a focal point. When assembled, the focal point falls on the reflective surface. A crank turn is encoded half-on / half-off by each of the 3 channels shifted 120° apart, as illustrated in FIG. 2B, resulting in 6 counts / turn. The encoder body size is 4.5mm in length (or 19.5mm with fiber cover) by 24mm diameter.

[0045] The motor can use any control architecture that pressurizes the 3 ports sequentially, full or half-step, open loop or with feedback from the optical encoder 3 piezoelectric valves are used per motor (Hoerbiger PS 10021 -641 A, Germany) contained within a MR Conditional interface box located close to the scanner but outside the 5 Gauss line and connected with 4mlong hoses. While 3 piezoelectric valves are used herein, it should be noted that this is included by way of example and should not be considered limiting.

[0046] FIGS. 3A and 3B illustrate perspective views of a diaphragm based and a piston- driven pneumatic stepper motor, respectively, according to an embodiment of the present invention. Diaphragm and piston version motors were built, as illustrated in FIGS. 3A and 3B. A PneuStep-D prototype is shown in FIG. 3 A, and a PneuStep-P prototype is shown in FIG. 3B. Manufactured components w ere made on FormLabs Inc. stereolithography 3D printers. The exemplary resins used are listed in Error! Reference source not found..

[0047] The resins used w ere Standard Clear for the body, body cap, and the 3 encoder case parts, and Tough 2000 for the hoop gear, output gear, pistons, crank shafts, and encoder code wheel. Essential surfaces, such as the cylinder bore, bearing housings, pin bores were finished with reamers; races of the output gear bearings and the piston heads were touched up with sandpaper in a lathe; taps were run in all printed helical threads; the gears were not finished.

[0048] Piston pins and crank pins were cut of Garolile or alumina ceramic rods. Screws and air port nipples were made of Nylon. O-rings are made of silicone. Bearings have plastic races and glass balls. Adhesive plastic reflective tape was glued on the face of the encoder codewheel, and the encoder uses plastic fibers. The balls of the outer gear bearings were intercalated with Torlon and Delrin, with the Delrin size being slightly smaller to act as a rolling cage. Optical fibers were 0.5mm core and 1mm outer diameters (PIU260U, Banner Engineering Corp.),Table 1: FormLabs Inc. resins used for each partPart ResinBody, body cap, 3 encoder case Standardparts ClearHoop gear Rigid 10KOutput gear, pistons, crank shafts, Toughencoder codewheel 1500

[0049] According to ASTM F2503, MR-safe is a device “that poses no known hazards resulting from exposure to any MR environment, MR-safe items are composed of materials that are electrically nonconductive, nonmetallic and nonmagnetic7'. The materials used to build the motors were selected as such, being an essentially “plastic” motor. This also facilitates FDA regulatory procedures and clinical translation. Per the ASTM, “an item composed entirely of electrically nonconductive, nonmetallic and nonmagnetic materials may¬ be determined to be MR-safe by providing a scientifically based rationale rather than test data”. In addition, parts made of the FormLabs resins were tested in the MRI together with experiments. According to tests and the ASTM F2503 scientific rational, all PneuStep versions are MR-safe.

[0050] Using pistons increases reliability especially for high duty cycle applications and reduces maintenance. Using pistons is also simpler. The piston version eliminated the hardware required to mount the diaphragms (See e.g. FIG. 1A vs. FIG. 1B, 12 less parts). The total number of fabricated parts in PneuStep1P is 6+3*3=15 and 3 more for the encoder. The other are inexpensive off-the-shelf components.

[0051] Eliminating the diaphragm mounting hardware also created more room to enlarge the piston diameter (diaphragm was 10mm outer diameter, piston is 14mm). The capacity of the motor has more than doubled, from 0.4cm3to 0.897cm3. Higher pow er motors can be made by increasing the capacity.

[0052] The updated design of the gears with involute shifted teeth geometry has enabled a finer motor step size and larger gear module compared to the original PneuStep. The gear transmission ratio depends inversely on the number of teeth difference between the hoop and output gears. In the new design this difference was minimized to 1. As such, the step size was reduced from 4° to 2.5°.

[0053] With 3 diaphragms / pistons and half-step control, the number of steps per crank turn is 6. The original PneuStep used quadrature encoding, therefore could not generate 6 counts to match the steps (only multiples of 4). As such, a 3 count codewheel was used to render 6 counts / turn. The motor could only step on every other count, which had to be accounted for in software. In the PneuStep1 and PneuStep1P. a fail-safe encoder, in a preferred embodiment a 3-channel encoder, with a 1 count codewheel is used for a total of 6 counts / tum, which are phased to match the steps of the motor. Most importantly, quadrature encoders are not fail-safe. With servo control, if a channel fails, a moving motor appears stationary and the controller becomes unstable, relying only on following errors to stop it within a normally large window As such, in medical applications, robots normally require redundant encoding to cope with the problem. With a stepper, the motor step counts may be used instead. In any case, a 3-channel encoder is simpler than 2 quadrature encoders and is fail-safe. If at least one channel fails (high or low), an impossible signal combination will be detected within just a turn (See, e.g. FIG. 2B. 000 or 111 are impossible). As such, the new encoder matches exactly the steps of PneuStep and is fail-safe.

[0054] Common pistons are cylindrically shaped to seal on the cylinder walls and facilitate manufacturing. Consequently, the piston must translate and so a connecting rod is commonly used to link the piston to a crank. PneuStep1P can be made this way too. but that would require 2 pins and a longer piston. For an air motor, however, a rubber O-ring can seal the cylinder. Since it is flexible, the piston can now be slightly tilted without leaking, and so it can be directlyconnected to the crank with only 1 pin, as shown. The piston allow s tilting with a barrel shape. This shape and the pin cooling / lubrication through the piston are original.

[0055] Original in both new versions are the air vents of the cylinders. Hoses are long and the air is cyclically pumped / released from one end. If the cylinders close the circuit at the other end, only the air next to the valves is being refreshed in the hoses. Within the cylinders the same air is repeatedly compressed / expanded. The thermodynamic work heats the air, hoses, and the motor. Some air can be made to escape from the cylinder through the piston air channel over the pin. For high duty' cycles, controlled air leaks can be made with calibrated / adjustable air vents within the cylinders. The leak creates a small air flow through the hoses discharging the heat.

[0056] Both new motors are low cylinder capacity < 0.9cm3and consequently low power. This was called for by slow, image-guided intervention robots that require low power in a small package. Making the larger one w ould give substantially more power. While speed is limited in any pneumatic stepper, PneuSteplP can be simply configured for higher torques from the cylinder capacity Increasing structural properties to handle higher torques should also not be a problem given PneuStep’s bearing supports. High torque gains should be achievable with small size increments. The PneuStep family of motors can be entirely 3D printed. Alternately, any suitable manufacturing method known to or conceivable to one of skill in the art could also be used.[00571 Side by side, the diaphragm version has been compared with the new piston version and have shown that the piston version is simpler, more reliable, and substantially more performant, virtually clearing all known weaknesses of the original design. The piston-driven pneumatic stepper motor eliminates the wearing diaphragm, adds a fail-safe encoder, reduced complexity, and shown simple and inexpensive 3D printed manufacturing. Like the original PneuStep, the PneuStep1 and PneuStep1P are entirely MR-safe and remain hollow-shaft motors, enabling rotary or translational outputs.

[0058] FIG. 4A illustrates a motor test stand, and FIG. 4B illustrates an image view of a testing setup for motors according to an embodiment of the present invention.

[0059] The motors were tested on a dynamic test stand, as illustrated in FIGS. 4A and 4B. An electric motor generates counter-torque for the pneumatic motor. Its stator is supported on bearings and is connected with an arm to a force sensor (full bridge strain gauge LCL-005 Omegadyne Inc., conditioned by an SCM5B38-05 Datafortli Corp, amplifier module and read by a U SB-6000 National Instruments DAQ) so that the torque applied by the motor runs entirely through the sensor. The force sensor was calibrated statically, with weights. The electric motor is a brushless DC motor (GL80, T-Motor Co.) with a Moteus r4.11 controller (mjBots Robotic Systems) and integrated magnetic encoder (dynamic error 0.02° at 1700 rpm, 0.082° RMS noise). The bearing, pneumatic motor, and electric motor axes are coaxial.

[0060] The force sensor has a systematic error (σsensor) of 0.5% foil span, the amplifier module (σamp) has a gain of 500, an accuracy of 0.03% full span, a linearity of 0.01% full span, and a 10 mVp-p noise, finally the NI DAQ (σDAQ) has a 26mV rated accuracy with 10 mV RMS noise. The peak-to-peak noise from the amplifier module is assumed to be a Gaussian distribution and will be divided by 6 to get an equivalent RMS noise metric. The estimated error in the test stand was calculated with the following procedure. Systematic errors (cr) were combined using the absolute sum to be conservative, as:&l°sensorl "h l^amp l d” l^daq ||o.5% X 2 — X 10 VexcX 5001 + Eq. 1I VexcI1(0.03% + 0.01%) x 10 V| + |26 mV| — 80mVRandom errors (p) were combined using the quadrature sum, as:I* {■ 2P = √(p²amp+ p²DAQ) = √((10 / 6 mV)² + (10 mV)²) = 10.14 mV Eq. 2Total errors (r) were then combined using the quadrature sum, as:r = √(σ² + p²) = 80.63 mV Eq. 3From the static calibration, the system was found to have a relationship of 0.190 Nm / V, therefore the torque measurement error is:

[0061] E = 80.63 mV X 0.190— = 0.015 Nm Eq. 4

[0062] The air supply is passed through a regulator to reduce the pressure to the desired levels for testing, run through a flowmeter to measure the flow, accumulated in a tank (7,5 L) to stabilize the pressure, lubricated, and passed to the manifold of valves that feed the pneumatic motor. Since the tested motors are steppers, their speed follows synchronously the frequency of the pneumatic pulses (steps), unless the motor skips. A PC sets the pneumatic motor in motion at a test speed and progressively increases the counter-torque with the electric motor until the pneumatic motor starts stalling persistently (5 times in a row with 5 steps following error), as detected by the optical encoder. The sensor registers the maximum torque value before stall. Air pressure, air flowrate, torque, and speed were logged during testing.

[0063] A bundle of four hoses was used, 3 for the ai r and 1 protecting the optical fibers (Pol urethane tubing bundle, 1 / 4” OD, 1 / 8” ID, URH8-0804-02T-050, Clippard Instrument). The dynamic test stand described above uses 7520 Series (King Instrument Company) flowmeters: 2C-11 model (0.1 - 1 SCFM) for low flow and 5C-05 model (0.8 - 8.2 SCFM) for high flow conditions, with a valve to switch between the two. They are calibrated from factory for air at a standard temperature and pressure (STP), 70°F (21.11 °C) and atmospheric pressure (0 PSIG, 760 mmHg) A correction must be made when measuring the flow of compressed air, depending on the actual temperature and pressure of the air The correction factor is given by the manufacturer in an online calculator or determined with a formula.However, intuitively, the formula may appear inverted. The confusion is also fueled by the online calculator, which is given for the purpose of sizing a flowmeter, not flow correction, and is therefore inverted. As such, the formula is explained, herein, in detail.

[0064] FIG. 5 illustrates a schematic diagram of a variable area flowmeter. Most common flowmeters are variable area flowmeters, also called rotameters. They consist of a float in a tube with a progressively larger cross-section over its height, as shown in FIG. 5. Tire airflow pushes the float up with a drag force F proportional to the square of the air speed, or flow; At equilibrium, this is balanced by the gravity of the float, mg, at a height measured on the calibrated STP scale. This height is therefore based on the square law of drag,mg = c·Q²_STP = c·(ρ_STP / ρ_a)·Q²_a Eq. 5^stp •?.where, PSTPand Paare pressures, Tstpand Taare temperatures,and Qaare flows in the STP, measured, and actual conditions, respectively. The constant c depends on the type of fluid, which is air in both conditions. Therefore,Qa= QmEq. 6a *stpgives the actual flow at Paand Ta. To be independent of actual test conditions, an adiabatic transform converts the actual flow into an equivalent flow at STP, QaSTP.and so, it inverts Eq. 6, as:stP _ n Atp _ [pstpTAPA Atp _ fpd Atp3 'v <11n stp rjp 111 Ia Aj I n a T * stp ^ r}stp ' 'p V IIIa I n stp r 'pawhere, QjTPis the actual flow expressed as an equivalent flow rate at STP in standard cubic feet per minute | SCFM],is the flow read on the flowmeter scale, Taand Tcare the actual and calibration temperatures in [°R] (Rankine °R = °F + 459,67), and Paand Pstpare the actual and STP calibration pressures in absolute values [PSI A] (PSIA = PSIG (gauge) + 14.7). respectively. In SI units:[“]=t12* °-0254)3 x60 X QSTP[SCFM] Eq. 9Finally, air compressor requirements can be calculated with Boyle’s law to obtain the flowat an inlet pressure P,.

[0065] FIGS. 6A and 6B illustrate graphical views of torque, pow er and air consumption versus speed with 4.5 m long hoses for the PneuStep-D and the PneuStep-P, respectively. Each experiment was repeated three times (marks) and averaged (curves). Both motor models were tested on the test stand following the same procedure. Ihe results of the diaphragm and piston models are shown side-by-side in FIGS. 6A and 6B respectively, respectively. The graphs use the same scale, for comparison, for air pressures ranging from 0.14 MPa to 0.48 MPa. This range is around 50 PSI (0.34 MPa), the air pressure common in MR rooms. Each experiment was repeated 3 times, and the values were averaged, substantially higher pow er. The PneuStep-D power peaked at 0.15 W with 36 steps / s vs. 0.5 W with 72 steps / s for PneuStep-P. These gains were not reflected in the air consumption. As shown in FIGS. 6A and 6B the flow- rates w ere similar, with a maximum consumption of approx. 11 L / min @ STP.

[0066] FIG. 7 illustrates graphical views of torque, power and air consumption versus speed at hose lengths of 0.5 m to 4.5 m long hoses for the PneuStep-D and the PneuStep-P,respectively. The PneuStep-P experiments were repeated with six hose lengths between 4.5 m and 0.5 m and constant 50 PSI (0.34 MPa) air pressure. The results are shown in FIG. 7. As shown, shortening the hoses roughly doubled the capable speed, increased torque, and more than quadrupled output power. The highest pow er measured was 2.17 W. A dip in the curves around 144 steps / s is common between all hose lengths, possibly due to the pneumatic valves used and dynamic flow effects Shorter hoses also required less air, as expected. With the shortest hoses, the pressure was increased to determine the maximum power of the motor. The peak power was 2.5W with 0.5 m hoses, at 80 PSI (0.55 MPa), and 65 RPM (156 steps / s). The motor w as tested at 50 PSI (common in MR rooms), at the speed that corresponds to its maximum pow er, and a counter-torque that is half of the maximum value. From FIG. 6B, these values are 20 rpm (48 steps / s) and 0.0875 Nm.

[0067] FIG. 8 illustrates a graphical view7of a PneuStep-P angular position error from step center and endurance-test. A test cycle, illustrated in FIG. 8, was defined by 4 moves: 10 turns in a positive direction (10T+), back to 0 (0 from 10T+), 10 turns negative (10T-), and back to 0 (0 from 10T-). Each move w as done with counter-torque opposing motion, the torque w as removed, and positions w ere recorded from the optical and electric motor encoders. Finally, with the motor holding its position statically at 0, positive and negative torques were successively applied and positions were recorded from the encoders (Slop+ and Slop-) to measure the overall play in the motor and quantify wear. Overall, 6 electric-optical measured position pairs were recorded per cycle, together with the step command.

[0068] Skip step errors w ere calculated as the difference betw een the optically measured and commanded number of steps. Angular position errors were calculated as the difference between the electrical measured and command angles. The overall experiment ran 30 cycles.

[0069] First, no step skips were recorded throughout. The angular position errors are shown in FIG. 8. The curves show the errors at the end of the 10 turns (10T+ and 10T-), back to 0 (0 from 10T+, and 0 from 10T-), and slop after applying the torque (Slop+ and Slop-), respectively. As shown, all errors were well within the step limits (2.5° / 2). The experiment took 77.92 min, during which the motor ran for over 60 min, without malfunction. Both cycle-to-cycle performance and slop were relatively constant, thus wear on the motor was not observable.

[0070] Developments in actuation for the MR environment bring incremental value over previous developments and may extrapolate to other motor designs. Developments include a novel crank-piston mechanism and a piston geometry that substantially enhances power within a confined volume and uses entirely MR safe materials.

[0071] Common piston mechanisms involve a rod connecting them to the crank, two pin joints, and the piston is cylindrical in shape. The Opposed-Piston stepper motor also uses this approach Here, a barrel-shaped piston is connected directly to the crank with a single pin. The approach is simpler and shorter in length. As a pneumatic stepper, the cooling and pin lubrication through the piston are also original. A classic translating piston stops at both ends of the stroke, and was shown to increase positioning errors Instead, the new tilting piston never stops fully, as shown in the supplement animation. Therefore, the tilting piston should reduce the static friction at the ends of the stroke.

[0072] A common critique of previous motors were their complexity. In the -P version, the hardw are required to mount the diaphragms is eliminated. The total number of fabricated parts in PneuStep-P is 6+3*3=15, and 3 more with the encoder. All others are common off-the-shelf components.

[0073] Eliminating the diaphragm mounting hardware also created more room to enlarge the piston diameter (the diaphragm is 10mm outer diameter, and the piston is 14 mm). As such, from -D to -P the capacity of the motor has doubled, from 0.45 cm3to 0.9 cm3, within the same overall motor size.

[0074] The increased capacity is reflected in the maximum torques, from 0.19 to 0.49 Nm and maximum speeds from 60 steps / s to 108 steps / s, respectively. Compounded, these resulted in a substantially increased power, from 0.15W to 0.5W with 4.5m hoses,

[0075] The current size of both versions is 70mm outer diameter. 25mm thickness, with a 10mm bore. If needed, elongating the motor by only 4mm will allow to double cylindrical capacity to nearly 2cm3, and may result in approximately INm of torque and 1W power under the same conditions above.

[0076] Air consumption, as well as the maximum speed and power, are highly dependent on the length of the hoses. With 4.5m long hoses, the cylindrical volume of the motor represents less than 1% of the overall volume with hoses, so most of the air is used to fill the hoses. For the MR environment, however, the long hoses are required to place the valves outside the 0.5 mTesla (5 Gauss) line, otherwise the system would lose its MR safe classification. As shown in Error! Reference source not found., air consumption is similar for the two motors and low. A medium size (24 ACFM @ 90PSI) compressor should be sufficient to drive 3 motors running continuously at full power over 4.5m hoses and 0.34MPa (50PSI).

[0077] Tests with various hose lengths of the piston motor showed that the hoses limit the performance of the motor substantially, as illustrated in FIG. 7. Tests with 4.5m long hoses are relevant to classic high-field closed-bore MRI scanners. However, with low-field, helium- free scanners, hoses may be shorter, depending on the application, and so take advantage ofimproved motor performance. As shown, with the common medical air at 50 PSI (0.34MPa), PneuStep-P can go twice as fast and produce over 2W. The highest recorded power during testing was 2.5 W. I’he Opposed-Piston stepper does not report power but can be estimated at 3.3W (0.07Nm and 454.5rpm at 70PSI = 0.48MPa) and 1.1W (25N and 454.5rpm at 0.48MPa) with a screw, in an overall motor volume of approx. 200cm3vs. 96cm3of PneuStep-P.

[0078] Another essential novelty of this report is the design of the integrated gearing with shifted involute teeth geometry. This enabled a finer step size, larger gear module, and resulted in higher stroke and cylindrical capacity, increasing the maximum load. At its time, the PneuStep tooth geometry was constrained by subtractive manufacturing limitations, constraints that are now waived by additive manufacturing. The gear transmission ratio depends inversely on the difference in the number of teeth between the hoop and output gears. In the new design, this difference was minimized to 1, reducing the step size from 4° to 2.5°. The RC-45 and RC-80 step motors also use a hoop gear and achieved a reduction of 6.9°. The Opposed-Piston stepper also includes 3 cranks and central gearing that is integrated with the crank mechanism, with a transmission ratio of 2.2: 1 and reported 54.5° full step size (possibly half with half-stepping).

[0079] Novel in this invention is also the optical encoder. Other stepper motors use 3 driving elements (minimum required) and half-step control, resulting in 6 steps per turn. However, the most common digital incremental encoder, the quadrature encoder, cannot generate 6 counts. The present invention includes a 3-channel encoder with a 1-count code wheel for a total of 6 counts / tum, as needed. Moreover, with transmissive fiber optical encoders, the ends of the source and receiver fiber pairs face each other, and the code wheel passes in between, obstructing or passing the light beam. Since fibers are routed to the motor from the same side, one of the 2 fibersmust be bent 180°. Fibers, however, normally have a relatively large minimum bend radius, and so the bend adds substantially to the encoder length. Instead, the new encoder uses a reflective codewheel with fibers on the same side, reducing length (4.5 mm, Error! Reference source not found.) and allowing attaching / removing the encoder on one side of the motor. This fail-safe 3-channel reflective MR safe encoder is novel.

[0080] The air vents of the cylinders are also novel. When stepping with long hoses, only the air next to the valves is being refreshed in the hoses, most air being trapped and repeatedly compressed / expanded with each step. In high duty cycles, the thermodynamic work heats the air, hoses, and motor. Small vents on the motor side of the circuit may controllably discharge trapped air to reduce heating, if needed.

[0081] Motors have broken down during the max torque tests due to significant repeated overloading. However, the 78 minute endurance test, with the motor running for over 60 minutes at half of the max torque showed no performance loss and no observable wear. This is well within the duty cycle of interventional MR robots, which typically have short runtimes to position a needle guide.

[0082] Other MR motor test stands commonly used weights or brakes to generate the counter torque. Because stepper motor output is pulsed, especially at low speeds, the inertia of the weights plays a significant role, but measurements take the gravity alone. Therefore, reports using weights are likely underestimating their motor's capabilities. With brakes, the counter-torque is applied only during motion, and the stand is not able to apply a torque to a stationary motor. Tests applied disturbances manually. To alleviate the above deficiencies, a dynamic stand was constructed with counter torque generated by an electric motor. Tests also used a dynamic stand.

[0083] Traditionally, control of servo pneumatic motors over long hoses has been imprecise. But comprehensive dynamic modelling has shown accurate control in position and force. The latest control of the PRIME motor showed outstanding results, as low as 2.23° set point error with 10m long hoses, and approx. ±10° with backdrive disturbances but no load. PneuStep-P position errors under load at half of the capable torque were approx ±1° and no more than the step size, ±1.25°. Moreover, PRIME’S servo motor peak power is 3W and PneuStep-P was 2.5W at most, with PRIME being approximately half smaller in volume (Approx. 47 cm3vs.96 cm3). On the stepper side, within 230 cm3the RC-80 achieved a very high 24W power with 0.3m long hoses. Power with long hoses (5.3m) was not reported, but max speed dropped nearly 5 times (240 to 51 steps / s)

[0084] Selecting a type of motor depends on the clinical intervention. An important advantage of steppers is that they are fail-safe; in case of malfunction, they can only stall or go back and forth on the same step. In contrast, servos may spin inadvertently (i.e. broken hose) and continue to spin until a following error is detected, plus the time it takes to exhaust the air from the hoses.

[0085] With servos, power and speed are superior regardless of the hose length. In general, if power is not a factor, a stepper is simpler and safer; otherwise, a servo may be preferrable.Finally, 3D printing is highly enabling for MR safe device developments for their “plastic” nature. Post processing with common tools is often needed to improve surface, dimensional, and geometric quality of critical features. All parts of the reported motors were either 3D printed or off-the-shelf components, 3D printing makes manufacturing accessible and affordable Overall, side-by-side testing of the PneuStep-D and -P motors showed superiority of the piston version in all regards.

[0086] For the diaphragm and piston motors, the minimum pressures required to operate were 0.21 MPa and 0.14 MPa, maximum speeds were 60 steps / s and 108 steps / s, respectively. At any speed, the torques of the piston motor were more than double their respective diaphragm values. At 0.48 MPa, for example, the piston model increased the maximum torque from 0.19 Nm to 0.49 Nm. on par with the increase in cylindrical capacity from 0.45 cm3to 0.9 cm3. Together, the higher speeds and torques resulted in

[0087] The advancements described herein can be combined into a diaphragm motor and a piston motor, respectively. There are also additional innovations that could be used independently in other motor devices. For example, the involute, shifted gear teeth geometry could be used with any gear driven motor device, including the original PneuStep motor. The 3-channel encoder could also be used with other motors, including the original PneuStep motor. It should be noted that all of the motors and innovations described herein can be manufactured in MR-safe and non-MR-safe formats.

[0088] It should be noted that aspects of the device, its control, and calculations can be executed with a program(s) fixed on one or more non-transitory computer readable medium. The non-transitory computer readable medium can be loaded onto a computing device, microprocessor, servo, server, actuator, device processor, smartphone, tablet, phablet, a Robotic Control Box, or any other suitable device known to or conceivable by one of skill in the art.

[0089] It should also be noted that herein the steps of the method described can be carried out using a computer, non-transitory computer readable medium, or alternately a computing device, microprocessor, or other computer type device independent of or incorporated with an imaging or signal collection device. The computing device for executing the present invention can be a completely unique computer designed especially for the implementation ofthis method. Indeed, any suitable method of analysis known to or conceivable by one of skill in the art could be used. It should also be noted that while specific equations are detailed herein, variations on these equations can also be derived, and this application includes any such equation known to or conceivable by one of skill in the art.

[0090] A non-transitory computer readable medium is understood to mean any article of manufacture that can be read by a computer. Such non-transitory computer readable media includes, but is not limited to, magnetic media, such as a floppy disk, flexible disk, hard disk, reel-to-reel tape, cartridge tape, cassette tape or cards, optical media such as CD-ROM, writable compact disc, magneto-optical media in disc, tape or card form, and paper media, such as punched cards and paper tape.

[0091] It should be noted that the software associated with the present invention is programmed onto a non-transitory computer readable medium that can be read and executed by any of the computing devices mentioned in this application, Tire non-transitory computer readable medium can take any suitable form known to one of skill in the art. The non-transitory computer readable medium is understood to be any article of manufacture readable by a computer. Such non-transitory computer readable media includes, but is not limited to, magnetic media, such as floppy disk, flexible disk, hard disk, reel-to-reel tape, cartridge tape, cassette tapes or cards, optical media such as CD-ROM, DVD, Blu-ray. writable compact discs, magneto-optical media in disc, tape, or card form, and paper media such as punch cards or paper tape. Alternately, the program for executing the method and algorithms of the present invention can reside on a remote server or other networked device. Any databases associated w ith the present invention can be housed on a central computing device, server(s), in cloud storage, or any other suitable means known to or conceivable by one of skill in the art. All of the information associated with the application is transmitted either wired orwirelessly over a network, via the internet, cellular telephone network, RFID, or any other suitable data transmission means known to or conceivable by one of skill in the art.

[0092] The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention.Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

Claims

What is claimed is:

1. A motor comprising:a hoop gear;an output gear;wherein the hoop gear and the output gear comprise teeth having an involute, shifted geometry’;a driving mechanism, wherein the driving mechanism is configured to engage the hoop gear and the hoop gear in turn engages the output gear.

2. The motor of claim 1 wherein the driving mechanism is a diaphragm.

3. The motor of claim 1 wherein the driving mechanism is a piston.

4. The motor of claim 3 wherein the piston comprises a barrel shape.

5. The motor of claim 3 wherein the piston is directly connected to a crankshaft for the hoop gear.

6. The motor of claim 1 wherein the driving mechanism is engaged with air7. The motor of claim 1 wherein the driving mechanism is engaged with air, and wherein calibrated air vents in close proximity' of the cylinder allow’ a small amount of air to escape.

8. The motor of claim 1 further comprising a three-channel encoder.

9. The motor of claim 1 wherein the motor is MR-Safe.

10. A pneumatic motor comprising:pistons; anda crank shaft;wherein the pistons are connected directly to the crank shaft.

11. The motor of claim 10. wherein the pistons are barrel shaped.

12. A device for actuating a target component of a motor comprising:an air-driven driving mechanism;wherein the air-driven driving mechanism is pressurized by air, which then causes the air-driven driving mechanism to actuate the target component of the motor.

13. The device for actuating a target component of the motor of claim 12 wherein the air- driven driving mechanism comprises a diaphragm.

14. The device for actuating a target component of the motor of claim 12 wherein the air- driven driving mechanism comprises a piston.

15. The device for actuating a target component of the motor of claim 14 wherein the piston comprises a barrel shape.

16. The device for actuating a target component of the motor of claim 14 wherein the piston is directly connected to a crankshaft for the motor.

17. The device for actuating a target component of the motor of claim 12 further comprising calibrated air vents configured to allow a small amount of air to escape.18 The device for actuating a target component of the motor of claim 12 further comprising a three-channel encoder.

19. The device of claim 18, wherein the three-channel encoder comprises a one-count code wheel.

20. The device for actuating a target component of the motor of claim 12 wherein the device for actuating a target component of the motor is MR-Safe.

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