Cable transmission-reduction for human limb, robotic arm, and the like

Abstract

A stackable cable reducer consists of a driving-side assembly and a driven-side assembly, which are coupled through a central axis. The reduction is characterized by a medial plane that separates the clockwise (CW) side from the counterclockwise (CCW) side. It includes a central pulley stack with a freely rotating first central pulley and a rotationally constrained stationary second central pulley. Both CW and CCW sides have proximal and distal sets of cambered guide wheels, which are inclined relative to the central pulley stack. A tensioned cable is routed around these pulleys and guide wheels, creating rotational motion and torque amplification between one set of cambered guide wheels and another when a corresponding segment is pulled.

Description

CABLE TRANSMISSION-REDUCTION FOR HUMAN LIMB, ROBOTIC ARM, ANDTHE LIKERELATED APPLICATION

[0001] This application claims priority benefit of U.S. Provisional Patent Application No. 63 / 593,207, filed October 25, 2023, which is hereby incorporated by reference.TECHNICAL FIELD

[0002] This disclosure relates to a modular cable transmission-reduction system configured to permit back-drivable torque amplification and speed reduction for use in diverse applications, including actuation of robotic machine members, rotation of artificial limb joints, and exoskeleton-based load-assist devices.BACKGROUND INFORMATION

[0003] Powered orthoses are robotic braces designed to assist individuals with limited arm mobility, particularly targeting the elbow and hand. These devices support and enable movement in affected joints, allowing users to regain functionality, such as lifting and grasping objects. Typically used in home medical settings, powered orthoses are often employed by individuals recovering from neurological conditions, such as strokes, or those suffering from upper-limb paralysis due to various health issues.

[0004] These systems often operate using myoelectric sensors that detect nerve signals in the user’s muscles, even when those signals are weak. The sensors amplify the signals to drive motorized components within the orthosis, providing the user with assisted movement. While powered orthoses have shown considerable benefits for patients with limited mobility, they are generally expensive due to the use of hand-molded parts and custom fitting processes, which require manual adjustments for each individual user. This high production cost, along with lengthy manufacturing times, can make them less accessible and limit insurance coverage.

[0005] Additionally, many powered orthoses tend to be heavy, which can reduce comfort for users, especially during prolonged use. Despite these challenges, powered orthoses remain an important tool for improving mobility in individuals with upper-limb impairments, though their cost and customization requirements present barriers to wider adoption.SUMMARY OF THE DISCLOSURE

[0006] An embodiment described herein provides a stackable cable reducer designed for back-drivable torque amplification and speed reduction. The stackable cable reducer includes a driving-side assembly located at the proximal end, which is coupled through a central axis to a driven-side assembly at the distal end. This configuration allows the driven- side assembly to rotate relative to the driving-side assembly. A medial plane is defined within the stackable cable reduction, positioning the central axis and dividing the system into two sides: a clockwise (CW) side, through which a first tensioned cable segment is routed, and a counterclockwise (CCW) side, through which a second tensioned cable segment is routed.

[0007] At the core of the stackable cable reducer is a central pulley stack. This stack includes a first central pulley at the lowest level, freely rotatable around the central axis, one or more intermediate pulleys stacked sequentially on top, and a stationary pulley at the uppermost level, which is rotationally constrained around the central axis. On both the CW and CCW sides of the stackable cable reducer, there are proximal and distal sets of cambered guide wheels. These wheels are arranged in spaced-apart manner along guide posts, oriented parallel to the central axis. The proximal guide wheels are positioned closer to the central pulley stack within the driving-side assembly, while the distal guide wheels are placed within the driven-side assembly. All the guide wheels are inclined upward relative to the lowermost level of the central pulley stack, guiding the tensioned cables toward both the medial plane and central axis.

[0008] The first tensioned cable segment enters the driven-side assembly on the CW side at the lowest level of the central pulley stack. It wraps around the first central pulley and proceeds distally, where it is routed around the first of the distal cambered guide wheels, then redirected proximally and upward to wrap around the next-higher intermediate pulley in the central pulley stack. This process continues as the cable progresses upward along the stack until it is finally wrapped around the stationary central pulley and fixed at the uppermost level of the stackable cable reduction. Similarly, the second tensioned cable segment enters the driven-side assembly on the CCW side, following an equivalent routing pattern around the pulleys and cambered guide wheels on its side until it too is fixed at the uppermost level.

[0009] When the first tensioned cable segment is pulled away from the driving-side assembly on the CW side, the driven-side assembly is caused to rotate clockwise about the central axis. As a result, the length of the first tensioned cable segment shortens while thesecond tensioned cable segment lengthens. Conversely, when the second tensioned cable segment is pulled away from the driving-side assembly on the CCW side, the driven-side assembly rotates counterclockwise, shortening the second tensioned cable and lengthening the first.

[0010] The stackable cable reducer may include additional features, such as a tensioner integrated into the driven-side assembly, with adjustable clamp screws and teeth for precise cable tensioning. Cambered guide wheels may be inclined to optimize cable guidance, while a flexible sheath can protect the cable along certain segments. A cosmetic shell may cover the cable, allowing adjustments without exposing internal components.

[0011] In a cable-drive transmission system, the stackable cable reducer is coupled with a motorized driver featuring a capstan for winding the tensioned cable, a position encoder for precise control, and a feedback control system with torque monitoring. The feedback system dynamically adjusts motor output based on real-time current sensing to prevent overtensioning and ensure safe operation. The motorized driver can include a control system with myoelectric sensors that detect muscle activation signals, selectively activating the motor based on user intent.

[0012] A linkage system using the stackable cable reducer can support assistive or robotic devices, employing end effectors on the driven-side assembly to assist limb movement. The linkage system may include a cable interchange positioned at arm joints to maintain cable tension across multiple reducers, enabling synchronized or independent joint motion, such as in elbow flexion / extension or shoulder abduction / adduction.

[0013] Additional linkage features may include upper arm supports and shoulder-mounted brackets to align stackable cable reducers and optimize force transfer, as well as sensor arrays for real-time measurement of muscle activation and joint angles. This data allows for dynamic adjustment of applied torque, providing safe, responsive assistance tailored to the user’s movements.

[0014] Additional aspects and advantages will be apparent from the following detailed description of embodiments, which proceeds with reference to the accompanying drawings.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0015] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0016] FIG. 1 is a pictorial view of a user’s torso while wearing on his or her back and left arm an assistive, lightweight exoskeleton cable transmission-reduction system having multiple, stackable cable reducers to facilitate motor-driven joint rotation about an elbow and shoulder for use in a rehabilitative, personal, or industrial setting.

[0017] FIG. 2 is a top plan view of a cable-drive transmission of the type shown in FIG. 1.

[0018] FIG. 3 is a side elevation view of a motorized driver in FIG. 2 but shown with its cover removed.

[0019] FIG. 4 is a simplified isometric view of components in a stackable cable reducer shown in FIG. 1.

[0020] FIG. 5 is a side elevation view of the components shown in FIG. 4.

[0021] FIG. 6 is an exploded view of the stackable cable reducer of FIG. 1, viewed from the bottom.

[0022] FIG. 7 is an exploded view of the stackable cable reducer of FIG. 1, viewed from the top.

[0023] FIG. 8 is another isometric view showing the top of the assembled stackable cable reducer of FIG. 1.

[0024] FIG. 9 is a detailed isometric view of an area identified in FIG. 8.

[0025] FIG. 10 is another simplified isometric view of components in a stackable cable reducer with two central pulleys.

[0026] FIG. 11 are a set of side elevation views showing simplified block diagrams of stackable cable reducer having different numbers of pulleys.

[0027] FIG. 12 is a pictorial view of a user’s torso while wearing on his or her chest and right arm another example of an assistive, lightweight exoskeleton cable transmissionreduction system having multiple, stackable cable reducers.

[0028] FIG. 13 is an isometric view of a stackable cable reducer of the type shown in FIG. 12.

[0029] FIG. 14 is an isometric view of a stack of modular guide wheel cassettes, in accordance with one embodiment.

[0030] FIG. 15 is an exploded view of the modular guide wheel cassette shown in FIG. 14.

[0031] FIG. 16 is a side elevation view of a motorized driver shown in FIG. 12.

[0032] FIG. 17 is an isometric view of a cable interchange suitable for use at a joint in an assistive, lightweight exoskeleton cable transmission-reduction system.

[0033] FIG. 18 is a side elevation view of the cable interchange shown in FIG. 17.

[0034] FIG. 19 is an isometric view of a cable interchange supporting multiple interchanges for corresponding stackable cable reducers at different downstream joints.DETAILED DESCRIPTION OF EMBODIMENTS

[0035] FIG. 1 shows an assistive exoskeleton cable transmission-reduction system 100, including a back-worn cable drive harness 102 and an arm- and shoulder- worn jointassistance linkage 104 in a protective shell 106. In the example of FIG. 1, back- worn cable drive harness 102 and arm- and shoulder- worn joint-assistance linkage 104 provide a mechanical advantage for multiple (e.g., three) degrees of freedom of motion at the shoulder and elbow joints by independent and coordinated actuation of cables in three stackable cable reducers 108.

[0036] Stackable cable reducers 108 include an elbow-located cable reducer 110 for assisting elbow joint flexion and extension, a deltoid-located cable reducer 112 for assisting glenohumeral joint flexion and extension (or hyperextension), and a scapula-located cable reducer 114 for assisting arm abduction and adduction. Each stackable cable reducer 108 also has an end effector 116 below the associated joint, respectively, a forearm end effector 118 with sleeve 120, an upper arm end effector 122 (i.e., upper arm support structure 124), and a shoulder end effector 126 with an associated angled bracket 128.

[0037] The term reducer (or reduction) is used in mechanical engineering and robotics. For instance, a speed reducer in robotics generally refers to a mechanical device that takes an input speed and torque from a motor (such as a motor driving a capstan) and outputs a lower speed with higher torque. Common types of reducers include gear reducers, belt drives, and chain drives. Such reducers are essential for tasks requiring higher force but lower speed. Cable reduction refers specifically to situations where the motion of a drive motor is reduced or geared down to apply a mechanical advantage at an associated anatomical or robotic-arm location (e.g., a joint). In the example of stackable cable reducer 108, speed of a motor drive shaft is reduced to increase the application of torque. The total amount of mechanical reduction produced by stackable cable reducer 108 is calculated using the following equation:Meeh. Reduction = {{Large Pulley Diameter) / {Capstan Diameter)) * Stack MultiplierEquation 1

[0038] where “Large Pulley Diameter” is the diameter of a central pulley (shown later) in stackable cable reducer 108, “Capstan Diameter” is the diameter of a capstan (shown later) rotated by a motor to wind a cable around the central pulley, and “Stack Multiplier” is thetotal number of stacked, freely rotatable central pulleys plus a final fixed (non-rotating) pulley at the top of the central pulley stack (also shown later) in one of stackable cable reducers 108. Thus, the mechanical reduction is a function of the ratio of the Large Pulley Diameter to the Capstan Diameter, multiplied by the Stack Multiplier.

[0039] In a mechanical system of this type, the terms driver and driven describe the relationship between two components. The component or source that imparts motion or power to another component is referred to as the driving or driver element. It is the part of the system responsible for initiating or supplying energy to the system. The driven component is the part of the system that responds to the input or power supplied by the driving element. It moves or operates in response to the actions of the driving component.

[0040] Each stackable cable reducer 108 acts as a driven component, which is independently driven by the clockwise (CW) and counterclockwise (CCW) winding of an associated driver in the back-worn cable drive harness 102. For instance, a scapula driver 130 is configured to wind cable 132 looped through scapula-located cable reducer 114 (i.e., to spin it clockwise or counterclockwise according to the rotation of scapula driver 130). Similarly, a deltoid driver 134 controls cable 136 looped through deltoid-located cable reducer 112, and an elbow driver 138 controls cable 140 looped through elbow-located cable reducer 110. A combination of a stackable cable reducer, driver, and associated cables is referred to as a cable-drive transmission.

[0041] As the name suggests, cable transmission-reduction system 100 provides both cable reduction and transmission of force (via cables). Cable transmission refers to a system by which motion or force is transmitted from one point (the motor) to another (the joint). As noted, there are three cable-drive transmissions in cable transmission-reduction system 100. The system also facilitates the transmission of force by maintaining equal tension at a joint through cable interchangers, examples of which is shown and described later with reference to FIG. 17-FIG. 19.

[0042] Skilled persons will appreciate that cable transmission-reduction system 100 and similar embodiments in this disclosure include a control system (not shown) and sensors 142 to determine which drivers to actuate and the direction in which to apply torque. For instance, myoelectric sensors may be applied to the user’s biceps and triceps; when the muscle signal from the biceps exceeds that of the triceps, elbow driver 138 is activated to increase elbow flexion. Conversely, when the triceps signal surpasses the biceps signal, elbow driver 138 is actuated to promote elbow extension. Various other control strategies are also possible.

[0043] FIG. 2 shows in greater detail a cable-drive transmission 200, which includes stackable cable reducer 108, a motorized driver 202, and a tensioned cable 204. At the left side of FIG. 2, stackable cable reducer 108 is shown as having a fixed portion 206 (also termed a joint-input-side unit) at its proximal end 208 and a rotatable portion 210 (also termed a joint-output-side unit) at its distal end 212. Fixed portion 206 and rotatable portion 210 are rotatably coupled at a central axis of rotation 214, which includes an internal pulley mechanism (the details of which are shown and described later) about which a first free end 216 and a second free end 218 of tensioned cable 204 are routed on opposing sides and fixed to stackable cable reducer 108. These first free ends 216 and 218 may optionally be routed through Bowden tubes 220 so that the lengths of tensioned cable 204 extending from a cable tensioner 222 to stackable cable reducer 108 have flexible sheaths and thereby protected in said tubes.

[0044] In selecting tensioned cable 204 for cable-drive transmission 200, various materials can be selected based on the application’s requirements for strength, flexibility, and durability. The choice of material ultimately depends on factors such as load capacity, weight, desired flexibility, and the environmental conditions in which the system will operate, with each material offering different benefits tailored to specific use cases.

[0045] Steel cables, such as stainless steel or galvanized steel, offer high tensile strength and durability, making them suitable for applications that involve heavy loads, such as industrial robotics or exoskeletons designed for heavy lifting. However, for systems that prioritize lightweight construction and flexibility, materials like Kevlar (an aramid fiber) and Dyneema (ultra-high molecular weight polyethylene) are also suitable choices. Kevlar provides high strength and resistance to heat and abrasion, while Dyneema offers a very high strength-to-weight ratio and superior resistance to chemicals and UV exposure, making both well-suited for lightweight and high-performance exoskeletons or prosthetics.

[0046] In applications where elasticity and smooth movement are important, nylon cables provide excellent flexibility and wear resistance, making them suitable for rehabilitation robotics or assistive devices. Polyester cables, while slightly less elastic than nylon, offer more stability and resistance to environmental factors, making them appropriate for outdoor applications or systems exposed to humidity. Advanced materials like carbon fiber- reinforced cables are favored in high-performance robotics due to their lightweight and high strength, though they are typically used where rigidity is desired. PBO fibers (polybenzoxazole) are another high-strength option, particularly suited for extreme environments due to their outstanding resistance to heat and chemicals. Additionally, hybrid cables that combine a steel core with a polymer coating can provide a balance of strength,flexibility, and protection, making them versatile for various robotic and exoskeleton applications.

[0047] In the context of cable-drive transmission 200, cable transmission-reduction system 100 is capable of back-drivability. Back-drivability means that external forces applied to the joints of a robotic arm or exoskeleton (such as through human movement) can cause cable transmission-reduction system 100 to operate in reverse. This allows the user to move freely or with reduced resistance when the system is powered down or when there is insufficient motor input.

[0048] In a back-drivable system, if an external force is applied to the output (such as a robotic joint or exoskeleton arm), it can cause the input side (like motorized driver 202 or capstan 302) to rotate in reverse, effectively driving cable transmission-reduction system 100 backward. This characteristic is particularly useful in robotics and exoskeletons, where smooth, compliant movement is desired, and cable transmission-reduction system 100 is responsive to external forces or allow free movement when little or no power is applied.

[0049] In robotics, a back-drivable system is useful as it not only demonstrates high efficiency but also forms the foundation of effective torque control. In a back-drivable setup, the motor can sense external forces applied to it (through current sensing) and compensate accordingly, allowing the drive to behave predictably under load. Accordingly, the disclosed systems, in some embodiments, constantly monitors the current draw — e.g., over 40,000 times per second — enabling rapid response for safe, controlled motion.

[0050] For example, if the drive is commanded to move 150 degrees, it initially moves quickly. However, if it encounters resistance (such as the user’s hand contacting a table), the system responds appropriately. Without back-drivability, the system would detect the slowdown and increase power to try to regain speed, potentially up to maximum power, which could pose a risk if the arm is immobile against the table. With torque control and back-drivability, the system senses a sudden spike in torque when the arm encounters resistance, prompting it to override velocity or position commands to ensure both user and device safety.

[0051] This concept extends to smaller forces and loads as well, meaning the device seeks to apply a minimal amount of force needed to achieve the commanded action. This not only conserves power but also provides smooth, efficient motion for every action.

[0052] Moreover, this torque control operates continuously, even when the system is at rest. If a load is applied to the user, the drive actively compensates to maintain the targetposition but up to the limits defined in the motion profile, ensuring safe operation at all times.

[0053] Shown on its side with its cover removed in FIG. 3, motorized driver 202 includes cable tensioner 222 operatively connected by tensioned cable 204 to stackable cable reducer 108. Cable tensioner 222 includes capstan 302 having a midshaft 304 around which tensioned cable 204 is coiled multiple turns. The uncoiled portion of tensioned cable 204 then has first free end 216 and second free end 218 extending from opposing ends of capstan 302, as shown in FIG. 2. In a typical embodiment, cable tensioner 222 may include a motor mount 224 through which a motor (not depicted) or other actuation means may be operatively coupled to capstan 302 to provide torque to rotate capstan 302 in a CW or CCW direction, which imparts rotation of rotatable portion 210 via tensioned cable 204.

[0054] For example, FIG. 2 and FIG. 3 depicts a scenario in which a CCW torque 226 is applied to capstan 302, it such that a portion of first free end 216 of tensioned cable 204 is uncoiled from one end of capstan midshaft 304 and a portion of second free end 218 of tensioned cable 204 is coiled about the other end of capstan midshaft 304. The coiling action of second free end 218 of tensioned cable 204 about capstan 302 is transmitted as an increased pulling (tension) force 228 at second free end 218 entering stackable cable reducer 108. As a result of this increased pulling (tension) force 228 transmitted by the uncoiling and coiling of first free end 216 and second free end 218, respectively, of tensioned cable 204, rotatable portion 210 at distal end 212 of stackable cable reducer 108 undergoes a CCW rotation 230 about central axis of rotation 214. Thus, by inducing a CCW or CW rotation of capstan 302 (using, for example, a motor under external control), a corresponding CW or CCW rotation may be effected at rotatable portion 210 of stackable cable reducer 108.

[0055] Depending on the particulars of the pulley mechanism configured within stackable cable reducer 108 (including pulley sizes and routing of tensioned cable about the pulley mechanism), the mechanical effect of stackable cable reducer 108 is to act as a reduction, such that a torque applied at capstan 302 is amplified at rotatable portion 210 and the speed of rotation of capstan 302 (as driven by an attached motor) is transmitted at a reduced speed to rotatable portion 210.

[0056] FIG. 4 shows a simplified view of internal components of stackable cable reducer 108. This is a simplified view because it omits (i.e., by transparency) all solid interior surfaces of its central pulley stack 402 so that just outlines are visible. Likewise, exterior housing surfaces are transparent in a driving-side assembly 404 and a driven-side assembly406 to review internal pulleys. One set of ball bearings is shown, but each large pulley has bearings inside of it, except for the last one in the stack that has no relative motion (explained below). Finally, a simplified capstan 302 is depicted for illustrative and operational purposes, although capstan 302 is not considered to be an operational element of stackable cable reducer 108.

[0057] Stackable cable reducer 108 includes at proximal end 208 and distal end 212, respectively, driving-side assembly 404 and driven-side assembly 406. Driving-side assembly 404 and driven-side assembly 406 are rotatably coupled through central axis of rotation 214 positioned on and extending continuously through a median plane 408 that divides stackable cable reducer 108 into a CW side 410 a CCW side 412. A first tensioned cable segment 414 is routed on CW side 410 of stackable cable reducer 108, and a second tensioned cable segment 416 is routed on CCW side 412 of stackable cable reducer 108.

[0058] Stackable cable reducer 108 includes central pulley stack 402, which, in this example, is comprised of a lowest central pulley 418, upon which is stacked a lower intermediate central pulley 420, a middle intermediate central pulley 422, then an upper intermediate central pulley 424, and ending with an upper stationary central pulley 426. All these pulleys are centered on and positioned along central axis of rotation 214. Further, all but upper stationary central pulley 426 are freely rotatable about central axis of rotation 214, while upper stationary central pulley 426 is rotationally constrained.

[0059] In the configurations shown, i.e., one having an odd number of pulleys in central pulley stack 402, the last pulley (e.g., upper stationary central pulley 426) is coupled to the output side. Because it is on the output side, it rotates at the exact same rate as the output. This means that relative to the cable, it has a 1 : 1 motion it always travels with it. Because it moves at this same rate, it does not need bearings, as they move together. On setups with a even number of stacks the final stack would need the bearings at it would be moving relative to the final layer and output side, but with this setup, the device is a larger (for its given mechanical reduction).

[0060] Stackable cable reducer 108 further includes four cambered guide wheel assemblies 428 430, 432, and 434 positioned about and adjacent to central pulley stack 402.Specifically, on CW side 410, cambered guide wheel assembly 428 is comprised of a proximal set of guide wheels 436 that are rotatably stacked in a spaced-apart manner along a proximal guide post 438, with proximal guide post 438 positioned within driving-side assembly 404 at proximal end 208 of CW side 410 and oriented parallel to central axis of rotation 214. Cambered guide wheel assembly 432 is also positioned on CW side 410, and iscomprised of a distal set of guide wheels 440 that are rotatably stacked in a spaced-apart manner along a distal guide post 442, with distal guide post 442 positioned within driven- side assembly 406 at distal end 212 of CW side 410 and oriented parallel to central axis of rotation 214. Similarly, on CCW side 412, cambered guide wheel assembly 430 is comprised of a proximal set of guide wheels 444 that are rotatably stacked in a spaced-apart manner along a proximal guide post 446, with proximal guide post 446 positioned within driving-side assembly 404 at proximal end 208 of CCW side 412 and oriented parallel to central axis of rotation 214. Lastly, cambered guide wheel assembly 434 is also positioned on CCW side 412, and is comprised of a distal set of guide wheels 440 that are rotatably stacked in a spaced-apart manner along a distal guide post 448, with distal guide post 448 positioned within driven-side assembly 406 at distal end 212 of CCW side 412 and oriented parallel to central axis of rotation 214.

[0061] Each cambered guide wheel in cambered guide wheel assemblies 428 430, 432, and 434 is inclined upwards from a periphery of stackable cable reducer 108 towards median plane 408 and upwards towards central axis of rotation 214. Further, each cambered guide wheel stacked within each of cambered guide wheel assemblies 428 430, 432, and 434 is spaced-apart and sized such that the lower side of a given cambered guide wheel is positioned at a height to receive a tensioned cable segment from a given stacked pulley in central pulley stack 402 and route it upward to the inclined side of said cambered guide wheel and onto the next-higher-stacked pulley in central pulley stack 402. This stepping up of a tensioned cable trajectory to the next-higher-stacked pulley in central pulley stack 402 provides an inclined path for tensioned cable 204 and is described in greater detail below.

[0062] The routing path of first tensioned cable segment 414 on CW side 410 and second tensioned cable segment 416 on CCW side 412 is well-illustrated in FIG. 5, which shows a slide elevation view of CCW side 412, where second tensioned cable segment 416 is most clearly visualized on the observer side of the side elevation drawing. Accordingly, the routing path of second tensioned cable segment 416 on CCW side 412 will be described below, with the understanding that an equivalent routing path is followed by first tensioned cable segment 414 on CW side 410.

[0063] As shown in FIG. 5, second tensioned cable segment 416 enters driving-side assembly 404 on proximal end 208 of CCW side 412 of stackable cable reducer 108, where it is routed medially around an optional, horizontally-oriented alignment pulley 502, then laterally and distally around lowest central pulley 418 at the bottom of central pulley stack 402. Second tensioned cable segment 416 continues toward distal end 212 where it is routed latero-medially about the first of distal set of guide wheels 450 making up cambered guidewheel assembly 434, and re-directed proximally and upward to lower intermediate central pulley 420. Second tensioned cable segment 416 proceeds laterally and proximally around lower intermediate central pulley 420 to proximal end 208, where it is routed latero- medially about first of proximal set of guide wheels 444 making up cambered guide wheel assembly 430, and re-directed distally and upward to middle intermediate central pulley 422. Second tensioned cable segment 416 continues its route laterally and distally around middle intermediate central pulley 422 onward toward distal end 212 where it is routed latero-medially about the second wheel of distal set of guide wheels 450 making up cambered guide wheel assembly 434, and re-directed proximally and upward to upper intermediate central pulley 424. Finally, second tensioned cable segment 416 proceeds laterally and proximally around upper intermediate central pulley 424 to proximal end 208, where it is routed latero-medially about the second wheel of proximal set of guide wheels 444 making up cambered guide wheel assembly 430, and re-directed distally and upward to upper stationary central pulley 426 at the top of central pulley stack 402, after which a termination end 504 of second tensioned cable segment 416 is fixed in place (shown schematically as a crimped with an aglet) atop stackable cable reducer 108.

[0064] With first and second tensioned cable segments 414 and 416 routed as described above, a pull-pull configuration is established for stackable cable reducer 108. In this configuration, when first tensioned cable segment 414 is pulled proximally away from driving-side assembly 404 on CW side 410, driven-side assembly 406 is caused to rotate CW about central axis of rotation 214 toward driving-side assembly 404. During this CW rotation of driven-side assembly 406, the total length of first tensioned cable segment 414 traversing CW side 410 is shortened and the length of second tensioned cable segment 416 traversing CCW side 412 is lengthened.

[0065] Similarly, in the pull-pull configuration described above, when second tensioned cable segment 416 is pulled proximally away from driving-side assembly 404 on CCW side 412, driven-side assembly 406 is caused to rotate CCW about central axis of rotation 214 relative to driving-side assembly 404. During this CCW rotation of driven-side assembly 406, the total length of second tensioned cable segment 416 traversing CCW side 412 is shortened and the length of first tensioned cable segment 414 traversing CW side 410 is lengthened.

[0066] Thus, stackable cable reducer 108 operates by application of a torsional load (or rotation) at capstan 302, for example by a motor operably connected to capstan 302, and that force is transmitted through tensioned cable 204 to driving-side assembly 404 of stackable cable reducer 108, and routed to central pulley stack 402, where the path of tensioned cable204 is directed successively upward to adjacent large pulleys of central pulley stack 402 by a cambered orientation of cambered guide wheel assemblies 428 430, 432, and 434 positioned distally and proximally about central pulley stack 402. The frictional engagement of tensioned cable 204 along opposing sides of the large pulleys of central pulley stack 402 allows rotation of capstan 302 to be transmitted to and actuate driven-side assembly 406 of stackable cable reducer 108.

[0067] In stackable cable reducer 108, there are four freely rotatable large central pulleys and one final fixed large central pulley comprising central pulley stack 402. Thus, the Stack Multiplier equals five. Referring back to the Equation 1, the number of pulleys in central pulley stack 402 (i.e., the Stack Multiplier) and the relative sizing (diameters) of capstan 302 and of the large pulleys used in central pulley stack 402 determines the amount of mechanical reduction conveyed to driven-side assembly 406 and its end effector 116 (FIG.1) attached thereto. More specifically, the speed and rotational travel imparted by a motor to capstan 302 is reduced at the end effector side, and the torque imparted by the motor is amplified.

[0068] For completeness, FIG. 6 and FIG. 7 show exploded views of stackable cable reducer 108, showing including additional internal and structural components. For example, stackable cable reducer 108 includes a lower mounting plate 602 and an upper mounting plate 604 for driving-side assembly 404 at proximal end 208. Likewise, there is a lower mounting plate 606 and an upper mounting plate 608 for a driven-side assembly 406 at distal end 212. These upper and lower mounting plates may be secured, for example, to end effector load components or fixedly mounted to a particular surface depending on the intended use cases.

[0069] Various internal structural components are secured between the plates and about central pulley stack 402. For instance, top-mounted cable guide adapters 610 and bottommounted cable guide adapters 612 serve as retaining structures within which cambered cable guide wheels may be placed, and which further serve a structural and directional support for tensioned cables traversing latero-medially about individual cambered wheels as the cable trajectory is directed upward to adjacent central pulleys in central pulley stack 402. When central pulley stacks include more than two pulleys, an intermediate cable guide cambered wheel spacer / adapter 614 is provided to facilitate vertical stacking and spacing a multiple cambered wheels as needed.

[0070] FIG. 8 and FIG. 9 show in greater detail intermediate cable guide cambered wheel spacer / adapters 614 to better illustrate their geometry and function as vertical spacersbetween consecutively stacked and spaced-apart cambered guide wheels. Intermediate cable guide cambered wheel spacer / adapters 614 have step-up guides to route tensioned cable 204 between adjacent pulleys of central pulley stack 402 (FIG. 4), and physical constraints to contain and direct tensioned cables routed therethrough, intermediate cable guide cambered wheel spacer / adapters 614 are important components for enhancing modularity, adaptability, and utility of the disclosed stackable cable reducers.

[0071] Turning to FIG. 10, an example of a minimal stackable cable reducer 1000 is shown. As before, stackable cable reducer 1000 includes a proximal end 1002 serving as a driving-side assembly (not shown), and a distal end 1004 serving as a driven-side assembly 1006. As described previously, driving-side assembly and driven-side assembly 1006 are rotatably coupled through a central axis 1008 positioned within a medial plane.

[0072] Stackable cable reducer 1000 includes a minimal central pulley stack 1010, which, in this example, is simply comprised of a freely rotatable first central pulley 1012, upon which is stacked a single, rotationally constrained stationary central pulley 1014, with pulleys 1012 and 1014 centered on and positioned along central axis 1008. A pair of cambered guide wheels 1016 and 1018 are positioned at distal end 1004 on, respectively a CW side 1020 and CCW side 1022, of stackable cable reducer 1000, with each cambered guide wheel inclined upwards as described previously for routing a looped cable from stationary central pulley 1014 to freely rotatable first central pulley 1012 (or vice versa).

[0073] FIG. 11 shows four additional examples of tension cable routing when different numbers of pulleys are stacked in the central pulley assembly. In each of these assemblies, the topmost positioned pulley is fixed (i.e., rotationally constrained), as indicated by the cross hatching immediately above each of the topmost pulleys, while the other pulleys are free to rotate. For each exemplary stack, a tensioned cable enters on proximal side at the lowermost pulley and is routed upward to the topmost pulley on by cambered wheels positioned and vertically spaced-apart (when desired) on the distal and proximal sides of the pulley stack. The fixation of the free end of the cable, after routing about the topmost pulley is notated in each exemplary stack by an “x” . Note that when the total number of pulleys in a stack is an even number, the free end of the tensioned cable is fixed (“x”) on the proximal side of the stack. When the total number of pulleys in a stack is an odd number, the free end of the tensioned cable is fixed (“x”) on the distal side of the stack.

[0074] FIG. 12 shows another example of an assistive exoskeleton cable transmissionreduction system 1200, but in this example cable transmission-reduction system 1200 includes a chest-worn cable drive harness 1202 and an arm-worn joint-assistance linkage1204. In contrast to arm- and shoulder-worn joint-assistance linkage 104 of FIG. 1, linkage 1204 includes two stackable cable reducers 1206, i.e., an elbow-located cable reducer 1208 and a deltoid-located cable reducer 1210. In other words, to further reduce weight, arm- worn joint-assistance linkage 1204 omits a scapula-located cable reduction. Accordingly, chest- worn cable drive harness 1202 includes two motorized drivers 1212: a deltoid driver 1214 and elbow driver 1216 with associated cables.

[0075] In operation, each stackable cable reducer 1206 performs a function similar to that performed by their counterparts in stackable cable reducers 108. Stackable cable reducers 1206, however, are each of a second type shown and described next with reference to FIG. 13. Likewise, drive motors of chest-worn cable drive harness 1202 are of a second type shown and described later in greater detail with reference to FIG. 16.

[0076] FIG. 13 is an isometric view of a stackable cable reducer 1206 of the type shown in FIG. 12. Stackable cable reducer 1206 includes an integrated tensioner 1302, which features clamp teeth 1304 and clamp screws 1306 on each side. To operate tensioner 1302, the user loosens clamp screws 1306, centers the joint to the desired middle of travel, and pulls on a loose cable loop 1308 using a spring scale (also known as a dial or hanging scale) to measure tension. Once the desired tension is achieved, the user tightens clamp screws 1306, locking the joint at the correct tension without damaging the cable.

[0077] This design allows the cable to remain loose past the clamps, enabling precise tension adjustment and accommodating any reasonable length of extra cable. This makes assembly easier since exact cable length is not critical. Additionally, the user can set the exact desired tension, avoiding excess tension that can cause added friction or stress concentrations, which may otherwise reduce cable lifespan. The extra loose cable can be covered by a cosmetic shell that encloses the joint. For high-tension applications, a pulley can be used around the hook of the scale to prevent the cable from bending beyond its minimum radius, ensuring repeated tension adjustments without cable damage.

[0078] FIG. 13 also illustrates a driven-side assembly 1310 and a driving-side assembly 1312, either of which could include a tensioner (depending on the number of pulleys in the stack). Driven-side assembly 1310 is similar to previously described configurations.Driving-side assembly 1312, however, includes guide wheels 1314 for changing an angle of cable as it leaves near the upper arm and enters the elbow location.

[0079] FIG. 14 shows a stack 1400 of modular guide wheel cassettes 1402 (one of which is shown in FIG. 15) that, according to one embodiment, are used to form a driven-sideassembly 1408. Skilled persons will appreciate that a similar stack may be used for the driving side.

[0080] Stack 1400 offers an advantage in terms of threading tensioned cable 204 around each guide wheel 1412. Specifically, each modular guide wheel cassette 1402 can be threaded while it is held apart from driven-side assembly 1408 and central pulley stack 1410, and then it can be placed onto an alignment pin 1404 for its side of stack 1400. When the side is completely stacked, a fastener 1406 is used to secure all modular guide wheel cassettes 1402 on that side of stack 1400. When both sides are completed, driven-side assembly 1408 is formed. Any loose tension is then removed using tensioner 1302 (FIG. 13).

[0081] FIG. 16 is a side elevation view of motorized driver 1212, which includes several key components for precise control and cable management. Motorized driver 1212 features an integrated servo BLDC motor 1602 and an optional magnetic encoder 1604 for enhanced positional accuracy.

[0082] In some embodiments optional magnetic encoder 1604 provides input to a feedback control system (not shown) that monitors torque output or cable position (e.g., as a function of capstan 1606 position). The feedback control system may then dynamically adjust motorized driver 1212 to prevent cable over-tension and ensure safe operation under varying load conditions.

[0083] Alignment gearing 1608 has a 1 :4 ratio, allowing for a controlled speed increase. The system also includes a guide rod 1610, a lead screw 1612 (e.g., .5 mm pitch M3), and a sliding stage 1614. A gear is attached to a capstan 1606 of motorized driver 1212, so that when capstan 1606 rotates, it moves sliding stage 1614 housing the Bowden tubes in sync. This linked motion ensures proper winding of the cable. Specifically, a gear adjacent to capstan 1606 is coupled to lead screw 1612, so when capstan 1606 spins, it also drives lead screw 1612. The threaded insert within sliding stage 1614 moves at a rate determined by the pitch of lead screw 1612 — in this case, an M3 lead screw with a pitch of 0.5 mm per revolution. With the 1 :4 gear ratio, the system achieves a 4* speed increase, resulting in a 2 mm displacement per revolution. This setup allows the 1.54 mm diameter cable to wrap around capstan 1606 without overlapping, which is useful for the long-term durability of motorized driver 1212.

[0084] Finally, a cable termination 1616 offers flexibility, as the cable can be terminated on either the input or output side of capstan 1606. The design is adaptable for different lengths of tensioned cable of some fixed combined length. As indicated previously, the totalcable length on sides “A” and “B” remains constant, so when capstan 1606 rotates in one direction, side A increases in length while side B decreases, and vice versa. The placement of cable crimps (aglets) is implementation-dependent, but in some designs, the crimps are positioned on the drive capstan. This arrangement allows for on-device adjustments of the cable’s “middle” position and tension (see e.g., tensioner 1302) without disassembly.

[0085] FIG. 17 and FIG. 18 show a cable interchange 1700 suitable for use at a joint 1702 in an assistive, lightweight exoskeleton cable transmission-reduction system, such as system 100 or 1200. In the example of FIG. 17, an input is modeled as a capstan 1704 around which tensioned cable 204 is wound. Tensioned cable 204 extends toward a cable crossover 1706 having two side-by-side pulleys 1708 and 1710. FIG. 18 shows how tensioned cable 204 is then crossed over through pulleys 1708 and 1710 and extends toward an output 1712.Although output 1712 is modeled as an angle-measurement angle measurement disc 1714 (which itself forms part of another crossover), skilled persons will appreciate that output 1712 may represent an input of a stackable cable reducer 108 that is coupled to an end effector or is located at an intermediate joint.

[0086] The purpose of cable interchange 1700 is to allow the cable from preceding joints to move freely through a central axis defined by joint 1702. As joint 1702 rotates, a minimal angle change is observed on angle measurement disc 1714. This angle change is governed by the arc length of pulley 1710’s motion. For instance, if joint 1702 rotates 90 degrees, the cable at the interchange moves by approximately: / \ 902*7r* ( 12.5 mm, the radius of interchange pulley r = 9.817 mmEquation 2

[0087] Given that the downstream joint affected by this ~10 mm cable shift typically has a linear cable travel range of 200-300 mm for approximately 180 degrees of motion, this change at the interchange would result in about a 6-degree shift (for 300 mm travel) to a 9- degree shift (for 200 mm travel). This minor deviation can be easily compensated for in software, ensuring smooth and accurate motion throughout the system.

[0088] FIG. 19 is an isometric view of a cable interchange 1700 supporting a stack 1902 of cable crossovers 1706. Each cable crossover 1706 has a separate tensioned cable for corresponding stackable cable reducers at different downstream joints. For instance, a first cable extends between scapula-located cable reducer 114 and deltoid-located cable reducer 112, a second cable extends between deltoid-located cable reducers 112 and elbow-located cable reducer 110, and so forth.

[0089] Compared to similar systems that utilize, for example, a harmonic drive assembly, the reduction systems deployed in cable transmission-reduction system 100 and cable transmission-reduction system 1200 are considerably less costly, lighter weight, and readily adapted to changing user needs.

[0090] The modular cable transmission-reduction systems described herein, including the stackable cable reducers in its various configurations, may be used to great advantage in numerous applications for torque amplification, reduction of rotational speed and angular travel at an end effector, back-drivability, and / or spatial or weight constraints on the transmission system. In addition, one or more stackable cable reducers may be employed in a series or parallel manner within an overall system to engender multiple degrees of freedom as desired in many engineering applications. Example applications include robotics-based systems employing feedback control, large scale automation and manufacturing, robotic surgery requiring fine control at the end effector mechanism, prosthetic and orthotic devices for functional restoration and rehabilitation, and load-assist systems such as robotic exoskeleton devices.

[0091] In light of this disclosure, skilled persons will appreciate that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of a claimed invention. The scope of a claimed invention should, therefore, be determined only by the following claims.

Claims

CLAIMSWhat is claimed is:

1. A stackable cable reducer configured for back-drivable torque amplification and speed reduction, the stackable cable reducer comprising: a driving-side assembly at a proximal end coupled through a central axis to a driven- side assembly at a distal end, such that the driven-side assembly is rotatable relative to the driving-side assembly, the stackable cable reduction further characterized by a median plane within which the central axis is positioned, the median plane delineating the stackable cable reduction into a clockwise (CW) side and a counterclockwise (CCW) side; a central pulley stack comprising a first central pulley disposed on and freely rotatable about the central axis, and a stationary pulley disposed on and rotationally constrained about the central axis; proximal and distal sets of cambered guide wheels on both the CW and CCW sides, stacked along guide posts and inclined relative to the central pulley stack; and a tensioned cable including segments routed around the first central pulley, the stationary pulley, and the cambered guide wheels, the tensioned cable to facilitate rotational motion and torque amplification of one set of cambered guide wheels relative to the other set of cambered guide wheels when a corresponding segment is pulled.

2. The stackable cable reducer of claim 1, further comprising a tensioner integrated into the driven-side assembly.

3. The stackable cable reducer of claim 2, in which the tensioner includes clamp screws and adjustable clamp teeth configured to allow for pulling and setting cable tension.

4. The stackable cable reducer of claim 1, in which each cambered guide wheel in the proximal and distal sets of cambered guide wheels is inclined at an angle relative to the central axis for guiding the tensioned cable in an inclined path along the central pulley stack.

5. The stackable cable reducer of claim 1, in which the central pulley stack includes at least one freely rotatable pulley and one stationary pulley.

6. The stackable cable reducer of claim 1, in which the tensioned cable includes a flexible sheath along portions of its length to reduce cable wear and protect the tensioned cable from external contaminants.

7. A cable-drive transmission, comprising: the stackable cable reducer as recited in claim 1; and a motorized driver connected to the stackable cable reducer via the tensioned cable, wherein the motorized driver includes a capstan configured to wind the tensioned cable and a motor operatively coupled to the capstan to rotate it in a clockwise or counterclockwise direction, thereby imparting rotational motion to the driven-side assembly of the stackable cable reducer.

8. The cable-drive transmission of claim 7, further comprising a control system with myoelectric sensors configured to detect muscle signals from a user, in which the control system selectively activates the motorized driver in response to detected muscle signals.

9. The cable-drive transmission of claim 7, further comprising a torque monitoring system within the motorized driver, wherein the torque monitoring system adjusts motor output based on current-sensing feedback to prevent excessive torque for operation in response to varying external forces.

10. The cable-drive transmission of claim 7, further comprising a cable interchange located at a joint proximal to the stackable cable reducer, the cable interchange configured to maintain cable tension across multiple reducers, thereby allowing independent or coordinated motion of multiple joints.

11. The cable-drive transmission of claim 7, further comprising a feedback control system that monitors torque output or cable position, in which the feedback control system dynamically adjusts the motorized driver to prevent cable over-tension and ensure safe operation under varying load conditions.

12. The cable-drive transmission of claim 7, in which the motorized driver further comprises a position encoder configured to track the angular position of the capstan for control of cable tension and torque applied to the driven-side assembly.

13. A linkage system for robotic or assistive devices comprising: the stackable cable reducer as recited in claim 1 to manipulate an end effector attached to the driven-side assembly of the stackable cable reducer for imparting motion to a limb or device; and a cable interchange, configured to allow for transmission of force via the tensioned cable routed through a joint before the stackable cable reducer.

14. The linkage system of claim 13, further comprising a protective shell covering the tensioned cable and cable interchange, in which the protective shell is configured to allow for tension adjustments while concealing components to protect movement of pulleys and cable lengths in the linkage system.

15. The linkage system of claim 13, in which the stackable cable reducer is positioned at an elbow joint, providing rotational support for elbow flexion and extension, and in which the linkage system further comprises a second stackable cable reducer positioned at a shoulder joint to provide torque-assisted motion for shoulder abduction and adduction, enabling coordinated assistance across both elbow and shoulder joints.

16. The linkage system of claim 13, in which the cable interchange is configured to maintain continuous cable tension between an elbow-located stackable cable reducer and a shoulder- located stackable cable reducer, thereby allowing smooth and synchronous movement between the elbow and shoulder joints during arm motion.

17. The linkage system of claim 16, in which the end effector attached to the driven-side assembly of the elbow-located stackable cable reducer comprises a forearm support configured to securely engage a user’s forearm, enabling the transmission of torque from a cable-drive transmission to assist with forearm movement during flexion and extension.

18. The linkage system of claim 13, further comprising a shoulder-mounted bracket for securing the cable interchange in alignment with the shoulder joint’s axis of rotation, allowing the linkage system to transfer force from the shoulder joint to the elbow joint without impeding a range of motion of a user’s arm.

19. The linkage system of claim 13, further comprising an upper arm support structure positioned between the shoulder and elbow joints, the support structure being configured to maintain alignment of stackable cable reducers along the arm, ensuring consistent force transfer throughout a range of arm movements.

20. The linkage system of claim 13, further comprising a sensor array configured to measure muscle activation, in which sensor data is used to dynamically adjust torque applied by the stackable cable reducers to assist a user’s arm movements.

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