Exobrake for improved load or precision of robotic arm

Abstract

An exobrake 330, 340 is an externally applied apparatus to reinforce a robotic arm 300 to improve a load capacity, or control, thereof. It comprises a brake 330, 340 having a rotary end 332, 342 and a

Description

Field This application relates in general to reinforcing structures for robotic arms, and in particular to structures that improve the load or precision of robots by applying external brakes around revolute joints of the robotic arm. Background Industrial serial manipulators are very well-known general purpose robotic arms that serve countless applications in industry. These typically comprise 6 revolute joints in series, although they could have 4-8, more often 5-7 joints, and could have up to half of their joints being non-revolute (e.g. prismatic, or possibly compound such as universal joints or cylindrical) instead of revolute. Herein ‘robotic arm’ is preferred over ‘manipulator’ even though the structures match, as the latter suggests moving objects to be their purpose. While industrial serial manipulators are often used to grasp, maneuver, and release bodies, that does not span the uses and applications to which robotic arms are employed. Consistent with the term ‘manipulator’, robotic arms are payload constrained in design and in use, in that the robotic arm is selected based on its payload capacity. Payload capacity stipulates a weight limit the robot can safely manipulate, which is a load that a robotic arm can resist and move in any of its degrees of freedom from any pose. This agrees with the mindset of a designer of a manipulator. When doing pick and place operations robotic arms encounter forces based on exertion of the servos of the robotic arm (absent collision, which is avoided). There are many use cases where a robotic arm is not needed to move heavier objects across a full range or envelope of motions, but rather must withstand greater than rated forces while in a far narrower range of poses: the robotic arm is needed to manipulate a relatively light end-effector, preferably with full range of motion, and then higher loads are applied, either by actuation of an end-effector of the robot, or through interaction with the robot end with: another robot; a moving or stationary body; tooling; or other element of the environment. For example, as any person who has used a cordless drill knows, the drill typically can be manipulated by the user in free space quite easily, as it is light, but when drilling through a material, a higher force is required to encourage the bit to enter the material and stabilize the drill. High control and heavy load for a drilling insertion motion, may be needed over a relatively small distance, and needs less mobility. There are many analogous drilling and joining processes and even some straightforward manipulation processes, that call for alternating between A) free movement of the robot ends under low force conditions, and B) heavier load or precision processes for an interval during which the robot itself has a small range of motions, or even no end displacement. Herein, these are called A / B processes. For example, if a gantry system needs to release and regrasp a heavy part, a light robot may collectively be incapable of supporting the load throughout a variety of poses, in that any joint that is torqued or wrenched by the load may exceed the joint’s limits. A remainder of the robot (other than the inconveniently posed joint) load may be fully able to support the heavy part’s load. A / B processes can require the development of high quasi-static process forces, or forces of high-static-low dynamic nature. Some robots are known as collaborative robots, or cobots, and as a class, they are particularly amenable to the present invention. Safety is of utmost importance for cobots. Safety is measured as the severity of the potential impact between the cobot and the body of a human operator. For this reason, a cobot has velocity and torque limitations to have low inertia and sensors for detecting collision with mechanisms for further reducing harm in contact with people, or other sensitive bodies. Commercially available cobots are designed for low impedance mechanical characteristics and actuation uses joint torque control using integrated torque sensors in the actuation chains. Thus, a cobot is designed and operated with maximal actuator speeds and torques that are safe for humans so that the cobot can be operated without a safety cage. Cobots provide the opportunity for human-robot interactions within flexible manufacturing systems where the cobot performs repetitive and non-ergonomic tasks while human workers contribute knowledge of the process and finalize difficult to automate tasks. Despite these obvious advantages, the deployment of cobots in industry is still limited because cobots have low payload capacity, and in some cases, insufficient accuracy. Many manufacturing processes exceed payload capacities of cobots. Cobots are mostly used in ‘pick and place’, packaging, palletizing, machine tending and quality inspection applications. Some potential solutions to provide greater cobot functionality while maintaining safety have been proposed that focus on providing a duality in stiffness depending on the 2 cobot's velocity whereby the stiffness of the cobot is augmented when the cobot velocity is low to provide a potential for withstanding higher external forces in quasi-static configurations. Two approaches have been proposed: Series Elastic Actuator (SEA) and Variable Stiffness; and Hybrid Actuation. In SEA, a high compliance coupling is added between the actuator and the link to decouple the actuator inertia from the link inertia and consequently to reduce the apparent inertia in impacts. The SEA and variable stiffness approaches are limited in the control bandwidth since there are two levels of control, one for SEA inner loop and one for the robot outer control loop. Also, the stiffness must continuously be modified in the controller, in real-time. In hybrid actuation, a pair of actuators is used in the cobot's joints to reduce actuator weight and consequently the effective inertia. Using redundant or hybrid actuators provides better power to weight ratios. The torque generation is distributed between the two actuators, one with a low frequency bandwidth and high force capacity and the other with a high frequency bandwidth and low force capacity. However, there is little or no ability to apply the above methods to increase the payload capacity of the cobot. In yet other approaches, some efforts have been made to disengage the cobot from the process load. For example, Automatic Drilling Units (ADU) are widely used in the aerospace industry for drilling aero structures. The ADUs are manually inserted into drilling jigs (with a guiding hole for each drilling point) and triggered to start an automated drilling cycle by assemblers. This is also called semi-automatic drilling. A cobot, instead of a human assembler, has been tested to operate the ADU. In a similar approach (using ADU and drilling jigs), two cobots (as two arms) attached to a torso on a mobile platform were used. Thus, it is known to use tooling to clamp up workpieces or otherwise absorb high loads of certain processes in which cobots play a role. However, these approaches are unsatisfactory because an assembler must put the drilling jigs in place before a drilling process and remove them after. Single-purpose jigs can be used in place of a great many robotic applications, for a price, but the chief advantage of a robot is the potential to reliably perform a same rote operation iteratively, and then be programmed to perform another task. Heavy, costly to design and build, jigs that serve a single type and layout of part are precisely the costs robots are designed to obviate. Symbiotic air cushions and wraps have also been proposed. In one attempt, pressure sensitive air cushions are tailored to a robot to reduce the impact injuries by reducing the apparent stiffness. Whenever contact occurs with a cushion, the motion of the robot is immediately stopped. In another attempt, an airbag-like safety-module for a cobotic end-effector covers sharp tools and is inflated when the cobot is moving fast and deflated in slow or no motion. While using air cushions permits higher safe velocities, the air cushion technology does not augment the load capacity or precision of the cobot. Thus, there remains a need for an enabling device and method by which a robotic arm can be modified to be safe while in A mode but provide a higher payload capacity or accuracy for B mode operations involving high quasi-static process forces or forces of high-static-low dynamic nature. More generally, a kit for reinforcing a revolute joint of a robotic arm is provided, and a robotic arm with the reinforcement assembled thereon. Summary A kit is provided herein for outfitting a robotic arm to increase load capacity or to improve control (i.e. accuracy) of the robotic arm. The robotic arm has a base, an end, and a serial kinematic chain of actuated, jointed links coupling the base and end. The kit comprises a brake mountable externally on the robotic arm, the brake having a stator end and a rotary end. The kit comprises mounting hardware for securing the stator and rotary ends to the robotic arm so that the stator end and rotary ends straddle a first revolute joint of the robotic arm. The brake ends and mounting hardware are configurable to form a brake that reinforces the first joint when assembled so that applying brakes to the mounted assembly stiffens the robotic arm by providing a splint of the first joint, in at least one disposed angle of the joint. When mounted and assembled on the robotic arm, the rotary end moves freely when the first joint is actuated and the brake is not applied, but rotation of the first joint is resisted when the brake is applied. A robotic arm with at least one reinforced joint is also provided herein. The robotic arm comprises: a base; an end; a serial kinematic chain of actuated jointed links coupling the base and end, the chain including at least one actuated revolute joint. The robotic arm further comprises a brake having a rotary end and a stator end, each of these ends respectively secured to either: the base and the 1st link of the robotic arm; or to two neighbouring links of the chain, and to no other links of the chain, so that the stator end and rotary end straddle a first revolute joint of the robotic arm. The brake ends are secured in a position to: allow the rotary end to move freely when the first joint is actuated and the brake is not applied; and, apply contact between the rotary end and stator end of the brake to resist rotation of the first joint when the brake is applied. Finally, a method of augmenting load capacity of a robotic arm comprises adding a exobrake comprising a brake having a rotary end and a stator end to the robotic arm, by affixing these two ends to the robotic arm to straddle a first revolute joint of the robot; and controlling the exobrake to: allow the rotary end to move freely when the first joint is actuated and the brake is not applied; and apply contact between the rotary end and stator end of the brake to resist rotation of the first joint when the brake is applied. The robotic arm is outfitted with an external structure that provides stiffness to the robotic arm during operations that require greater load capacity with only minor limitations to mobility during operations that do not require greater load capacity or control. The assembled kit is an external (to the robotic arm) structure in that it surrounds the existing robotic arm. We will call the assembled kit an exobrake, and its action on the respective joint of the robotic arm and on the arm itself, a splinting or splint. The exobrake can be added or removed from the robotic arm in that the robotic arm can be used with or without the exobrake with different effect. Without the exobrake the robotic arm has a lower inertia and can be used for all of the purposes for which the robotic arm is designed and equipped. With the exobrake added, the robotic arm can be used for A / B processes for which load capacity and control limitations of the robotic arm without the exobrake, is not provisioned. In some embodiments, the kit includes two exobrakes. If the two exobrakes are to splint neighbouring joints of the robotic arm, mounting hardware for brake ends of a common link may be unified such that one monolithic part may be used for mounting each of these brake ends to that common link. This may simplify assembly, but also serves to reinforce that common link, and forms an exostructure that spans the two first joints and the common link. If such an exostructure starts at the base, we refer to it as an exoskeleton, which is desirable for most greatly increasing a stiffness and control over robotic arms. The base and rotary ends of the brake straddle a single revolute joint of the robotic arm (i.e. one and only one). In some embodiments, a lighter of the base and rotary ends is secured distally to the revolute joint, with respect to the base of the robotic arm, while a heavier of the base and rotary ends is secured proximally to the revolute joint, with respect to the base of the robotic arm. Herein, the exobrake includes at least one brake, each brake end secured respectively to two adjacent links (or the base and the 1st link) that straddle the single revolute joint of the robotic arm. Herein the mounting hardware for each end preferably comprises at least one tensioning brace that at least partially surrounds the link to secure the end of brake to that link without perforating or penetrating the link. Certainly band clamp structures are preferred as lightweight, stiff joining mechanisms, especially if the band clamp has suitable tribological coatings that enhance frictional engagement to prevent revolution around the link and translation up and down the link, however a complete encircling of the link is not necessary, as a clamp or jaw hingedly extended to grasp the link more than 60 or 70% of the perimeter of the link, if it is a link of circular cross-section as a most difficult to grip scenario, can be sufficient, albeit at a penalty to weight and stiffness. The band clamp defines at least one rigid end, possibly a buckle and possibly a tensioning piece, to which the brake end is affixed. Screws, nuts and bolts, and cotter pins may be used to buckle the band clamp together, tension the band clamp for securing to the link, and affix the brake end to the clamp. The clamp, or collectively the clamps, must distribute load on the arms to avoid undue stress concentrations that may otherwise arise from the load taken by the exobrake, and thus one or more stiffeners may be provided between two or more band clamps running along the link between the two bands. Penetration of the link is to be avoided for most robotic arms. Any material loss of the link is generally proscribed by manufacturers, and likely to void warranties. Advantageously clamping around the links can avoid weakening the link in any manner, and is preferred. The mounting hardware may include a set of parts that admits of multiple configurations to allow the brake to splint two or more different joints of one or more models of robotic arm. The mounting hardware preferably includes at least 3, and preferably 5 shims for independent precision alignment of the brake end with respect to the link. In some embodiments, the brake controller is configured to be integrated with an existing controller of the robotic arm, whether this is the robot controller itself, or a process controller used to control an end effector that is outside of the capabilities of the robot controller. Since the exobrakes are passive during robotic motion, control of the exobrake can be considered a separate process from motion control of the robotic arm. Therefore, in some embodiments, control of the exobrake could be limited to input / output (I / O) control (logic control) that is already included in the existing controller of the robotic arm. One way of enabling robot or process control processor to control the brakes is to provide the brakes with electronic control. This may be provided by coupling a computer on the exobrake with signaling from the processor, by wired connection or wireless signaling. Another way is to couple a pneumatic or hydraulic line that directly controls actuation of the brake to a service port of the robotic arm or the end effector. The exobrake may also include sensors, actuators, controllers, or other devices required for installation and operation of the exobrake, which are not included with the robotic arm for which the exobrake is designed. In some embodiments, the exobrake further comprises at least one sensor. In some embodiments, the at least one sensor is configured to determine the actuation condition of the at least one brake, such as a minimum separation of a brake pad of the stator end and a rotary friction surface of the rotary end, or a clamping force therebetween. While such sensors may be preferred in some embodiments, a measured resistance to commanded low force or speed motion of the joint when solicited may be used to gage state of brake application instead. Any suitable brake can be utilized, most of which are inherently mechanical and tribological in nature, but actuated mechanically via an electromechanical, pneumatic or hydraulic force. Magnetorheological braking is emerging as an alternative. Mechanical brakes include, for example, disk brakes, drum brakes, cone brakes, band brakes and the like, and their calipers or other movers with brake pads or surfaces for moving into contact with the rotary ends. In the foregoing examples and embodiments, all rotary ends are illustrated as disks in part to simplify presentation. It will be noted that one of the challenges of design and assembly of exobrakes is the need to provide a continuous hoop of brake disk material around the link (and for which more remote placement of the links is sometimes chosen). This is very important if the exobrake is required for locking at any angle of the splinted joint. However, in many cases, it is only for joint angles that are higher than a threshold from a nominal pose for which an exobrake would typically be required. Accordingly any sector of a rotary end of a brake can advantageously be used instead of a full 360° brake. If a brake rotary sector is used, a separate alignment fin placed substantially complementarily to the sector of the brake rotary sector, around the joint, may be preferred to ensure alignment and avoid any contact when the rotary sector enters the jaws of the stator. Alternatively jaws of the stator may be formed with uncommonly large actuation to admit the rotary sector without question when the brakes are not applied. In some embodiments, the exobrake comprises a brake disk or brake drum or cone affixed coaxially with an axis of a rotary link of the robotic arm. Applicant’s WO 15 / 186095 teaches a particularly lightweight brake having an aluminum, or aluminum matrix composite (such as that defined in Applicant’s patents in Canada, USA, Germany, and UK based on WO 14 / 121384) body with a cold-sprayed iron-based layer, covered by a wear resistant friction coating. The contents of both of these applications are incorporated herein by reference where allowed by law and practice for the teaching of these options. Note the AIMC taught in this latter reference can be used to fabricate a number of the parts, especially lightweight, stiff parts of the brake and the mounting hardware. In some embodiments, the exobrake comprises at least one disk brake. A disk brake comprises a rotating disk (the rotary end) and a stationary caliper (the stator end) that engages the disk when actuated to prevent rotation of the disk. Thus, in some embodiments, the at least one brake comprises a brake comprising: a disk secured to a link or the base of the robotic arm; and, a caliper secured to an adjacent link to the link or base, whereby actuation of the caliper prevents the disk from rotating thereby preventing the joint straddled by the brake from rotating about the rotation axis. The caliper, disk, mounting hardware, and links (or link and base) are stiff, and the force applied by the caliper on the disk together endow the exobrake with a stiffness that exceeds the rated stiffness of the joint and thus allow the robotic arm with the exobrake installed, to be used in process that exceed the payload capacity of the robotic arm. The disk and the caliper are affixed on the robotic arm on different sides of the joint about which the link rotates. The disk may be secured to the robotic arm at a portion that rotates about the rotation axis of the joint while the caliper is affixed to a portion that is stationary with respect to the rotation of the joint. In some embodiments, the disk is affixed to the rotatable link. Engagement of the caliper with the disk resists (i.e., slows or prevents) rotation of the link and thereby stiffens the joint at which the rotation of the link occurs. In some embodiments, the disk has a central axis about which the disk rotates, which is aligned with the rotation axis of the link. If there are two or more brakes, they may be of the same or different types and sizes. In some embodiments, the 1st brake is operable to resist the rotation of the 1st joint and the 2nd brake operable to resist the rotation of the 2nd joint. In some embodiments, the 1st brake comprises a 1st disk and a 1st caliper, and the 2nd brake comprises a 2nd disk connected to the robotic arm and rotatable with a 2nd link and a 2nd caliper connected to a base. Actuation of the 2nd caliper resists, preferably prevents, the 2nd disk from rotating thereby resisting, preferably preventing, the 2nd link from rotating about the 2nd rotation axis. In some embodiments, especially where the kit is used to retrofit an existing robotic arm and a disk brake is used in the exobrake, the exobrake may comprise shims or alignment screws to help secure the disk so that the central axis of the disk is aligned with the rotational axis of the link. Further, the caliper may be adjusted to open significantly 8 wider than the thickness of the disk to permit automatic adjustment of the caliper to the position of the disk. In some embodiments, at least one exobrake is utilized to provide further stiffening across adjacent joints of the robotic arm. For example, in some embodiments, the exobrake comprises two or more exobrakes for two or more distinct joints of the robotic arm. If two joints are adjacent (i.e., joints with no other joint therebetween) and each of the adjacent joints is provided with a brake, mounting components for the two adjacent brakes may be unified and / or shared. In such configurations, it is useful to utilize the exobrake to provide further stiffening across the adjacent joints. In some embodiments, a plurality of exobrakes is used to provide further stiffening of the joints and links. The exobrakes may extend serially from the base to a final joint in a series of joints, to form an exoskeleton that essentially makes the serial kinematic chain into a parallel kinematic chain to the extent that weight is borne by both the robotic arm and the exoskeleton, but essentially remains a serial kinematic structure to the extent that the splinted joints are left free or under low load. The exostructure spanning the joints and links of the robotic arm stiffen both the joints and links of the robotic arm. The use of exobrakes is preferred if the links of the robotic arm are not sufficient for the desired A / B tasks. Avoidance of exobrakes is preferred if weight penalties of stiffening the links are of greater concern. As exoskeletons extend from the base serially to 2-3 joints, some (and possibly substantially all) of the weight of the exoskeleton is borne by the base. An exobrake comprises at least one rigid element that unifies the respective ends (rotary or stator) of two brakes of a common link. The at least one rigid element may have a greater load capacity than a link of the robotic arm, but the additional stiffness provided by the at least one rigid element definitely increases load capacity of the robotic arm. The rigid elements are external to the links of the robotic arm. The exobrakes, when the brakes are applied, stiffen the joints of the robotic arm. In some embodiments, two or more joints are stiffened. In some embodiments, one or more of the joints are each stiffened by at least two rigid elements. In some embodiments, at least one of the rigid elements is rigidly connected to and extends between two joints via a passive rotary coupling. In some embodiments, the rigid element comprises a strut, a hollow cylinder, a plate or a combination thereof. The rigid element may be straight or have one or more bends. The rigid element will generally have a form required by the shape of the brake ends and the rotation axis of the joint straddled by the brake ends. In some embodiments, a joint selected to be stiffened by an exobrake, is a joint that experiences the largest moment during operation of the end-effector and / or is the least in line with a reaction force generated by the end-effector during operation. In some embodiments, the robotic arm is stiffened at a 1st joint, coupling the base of the robotic arm to a 1st link (a furthest joint from the end-effector). In some embodiments, the robotic arm is stiffened at a 2nd joint. In some embodiments, the 1st and 2nd joints are both stiffened. Brakes provided to the joints that are closest to the base of a typical serial robotic arm offer superior stiffness advantages and allow for substantially higher load processes than the rated load of the robotic arm. Typically, if only one brake is used, the 2nd, 1st, and 3rd joints are the most likely splinted (by order of likelihood). In some embodiments, the mounting hardware includes clamps or threaded couplings that secure the brake ends (rotary and base) to respective links. To avoid weakening the link, the clamping or threaded coupling preferably does not involve any added bores into any part of either of the links, but rather involves encircling or grasping the links. In some embodiments, any threaded coupling involves both box and pin threads on the mounting hardware or brake end. Components of the external structure may be made of any suitable material, for example steel, aluminum, metal composite, polymer, polymer composite and the like and combinations thereof. Known robotic arms comprise light-weight links, light-weight motors (e.g., brushless DC motors) without housing, and harmonic drive gears. Each joint between the links is usually equipped with a torque sensor, a link position sensor and a motor position sensor. Impedance control is designed at the joint level and the robot level to guarantee operator safety along the entire robotic arm structure. The robotic arm typically comprises a base for supporting or anchoring the robotic arm on an external surface (e.g., the ground or floor, or a motorized vehicle or platform), and includes at least 4 actuably jointed serial links, a majority of which being revolute-jointed. In some embodiments, the robotic arm or the kit further comprises a skin or pneumatic contact protector for covering at least the brake and mounting hardware, to reduce collision force with humans. The skin or protector may further comprise a sensor for sensing contact with a human. The robotic arm described herein may be used in tasks that were previously reserved for large, more expensive industrial robots, thus reducing the capital investment, industrial footprint, and safety requirements, while allowing an operator to access the process area to perform inline visual quality control. Furthermore, the issues with clearing safe spaces for robots can be entirely avoided with the use of the present robotic arm. Examples of manufacturing operations to which the robotic arm can be applied include drilling, hammering, countersinking, fastener insertion, collar insertion, part finishing, clamping, riveting and friction stir spot or stitch welding and the like, particularly on workpieces, for example in the aerospace and automotive industries. While most of these applications involve end-effectors that apply forces that exceed a payload of the robotic arm, it is not necessarily the case, as the excessive force that mandates the external structure can come from the environment and not the end-effector itself, and certainly can come from interactions with other mechanized machines. Therefore, in some embodiments, the end-effector may be a device that drills, hammers, countersinks, inserts fasteners, inserts collars, finishes parts, clamps, rivets or friction stir welds. In some embodiments, the robotic arm is applied in a robot, for example a collaborative robot. Application of the robotic arm to collaborative robots (cobots) offers improved load capacity without sacrificing safety because the external structure immobilizes the cobot during operation of the end-effector or other B mode activity, and, when used, the one or more exobrakes provides greater stiffness and durability for the cobot by absorbing environmental forces experienced by the cobot. An end-effector on the cobot can therefore generate more force than was previously permitted because of safety concerns, while not damaging the robotic arm or causing a safety concern for human operators in the operational area. Stiffening of joints of the cobot and immobilizing the cobot during operation of the end-effector therefore provides the ability to use cobots in a wider range of process applications. While the external structure adds weight, and therefore inertia to the robotic arm, resulting in relatively small performance penalties (e.g., reductions in velocities and loss of range of motion when the exobrake is actuated), the use of the external structure permits increases in forces that are not possible without the external structures. The kit permits outfitting (be it by retrofitting, refurbishment, refitting, or OEM fitting) existing robotic arms thereby extending the usefulness of a robotic arm without the need to build or purchase an entirely new robotic arm for A / B tasks. A cobot’s load capacity is therefore augmented by adding an external structure symbiotically integrated to passively follow the cobot’s motion. The external structure is designed to accommodate the range of motion of the cobot when the exobrake is not engaged. When applied to a cobot, the external structure can be designed to minimally impact safety for human coworkers. Once the cobot reaches programmed task points, the exobrake is activated on one, all or a subset of the cobot’s joints. Once the exobrake is activated, there is no further motion at those joints, but the remainder of the joints can be operated as usual to provide a reduced range of motions. Motion of the end-effector is unimpeded, and the end-effector can apply a larger load to the immobilized robot than the robot can sustain were it not for the exobrake. During a task, the applied force by the environment to the cobot (by the end-effector or the environment) is supported by the external structure, not by the joints and links of the cobot. The external structure can have a higher structural load capacity than the robot itself. It is therefore possible to apply a greater force through the end-effector of the cobot than the force for which the cobot is rated. Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. Brief Description of the Drawings For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: FIG. 1 depicts a schematic diagram of part of a robotic arm (base to 2nd link) having an exobrake at a 1st joint. FIG. 2 depicts a schematic diagram of part of a robotic arm (base to 2nd link) having an exobrake at a 2nd joint. FIG. 3 depicts an embodiment of a part of a cobot having exobrakes at 2nd and 4th joints. FIG. 4 depicts an embodiment of a cobot equipped for drilling and having a complete exoskeleton. FIG. 5A depicts a 2nd embodiment of a cobot equipped for drilling and having a partial exoskeleton. FIG. 5B depicts another view of the cobot of FIG. 5A. FIG. 5C depicts an exploded view of the partial exoskeleton of FIG. 5A. FIG. 5D depicts a schematic diagram of a hydraulic system for the exobrake of the cobot of FIG. 5A. FIG. 6 depicts a flow chart showing an embodiment of a drilling process utilizing a cobot of the present invention. FIG. 7 depicts a graph of angular position of a 1st joint (qi, radians) of the cobot of FIG. 5A vs. time (ms) showing the deviation of the joint from a target position when the cobot has the exobrake engaged vs disengaged. FIG. 8 depicts a graph of force (N) vs. time (ms) showing the clamping force that the cobot of FIG. 5A can apply with and without the exobrake engaged. FIG. 9 depicts a graph of real angular speed (deg / sec) vs. commanded angular speed (deg / sec) at the 1st joint of the cobot of FIG. 5A showing the deviation of the real angular speed from the commanded speed with and without the exobrake engaged. Detailed Description FIG. 1 depicts a schematic partial diagram of a robotic arm 10 having a base 11 for supporting the robotic arm 10 on a floor or ground in a work area, and the first two of its links 12 connected serially to the base 11. Subsequent links and joints and the end (with or without an end-effector) are not shown. The illustrated links 12 comprise a 1st link 12a rotatably connected to the base 11 at a 1st revolute, actuable, joint 14a and a 2nd link 12b rotatably connected to the 1st link 12a by a 2nd revolute, actuable, joint 14b. The 1st joint 14a permits rotation of the 1st link 12a about a substantially vertically oriented rotation axis A-A. The 2nd joint 14b permits rotation of the 2nd link 12b about a substantially horizontally oriented rotation axis B. While typical robotic arms have each link oriented so that a longitudinal extent of the link is disposed on axis of the base-proximal joint, as the 1st link is shown to be, FIG. 1 shows the 2nd link 12b oriented at an angle to this axis. If the robotic arm were to be 13 conventional in this regard: the 2nd link would extend into the page and be occluded by the 2nd joint, and link 12b as shown might be a 3rd link; or, the axis of the 2nd joint, instead of B, would extend parallel to the second joint. Except for how it affects a working envelope and mechanics of the robotic arm, there is no reason to require that the robotic arm according to the present invention be conventional in this respect. The robotic arm 10 has an exobrake 30 for splinting the 1st joint 14a. The exobrake 30 comprises a disk brake with a caliper 31 and disk 32. The disk 32 is rigidly attached to the 1st link 12a. The caliper 31 is securely mounted on a caliper mount 33 and positioned so that the disk 32 is between jaws of the caliper 31. While the schematic illustration shows the disk 32 inside the jaws of the caliper, it will be appreciated that this would typically be occluded by the caliper, nonetheless it is helpful for envisioning the operation of the brake. The caliper mount 33 is rigidly attached to the base 11. The disk 32 rotates with the 1 st link 12a relative to the stationary caliper 31 and mount 33, unless the caliper 31 is actuated to clamp the disk 32, thereby immobilizing the 1st joint 14a and the 1st link 12a. A motor for rotating the 1st link 12a about the rotation axis A-A and attendant electronics (including a controller), gears and the like, are situated in the 1st joint 14a, and are inherent parts of the robotic arm, and the 2nd joint 14b is similarly equipped to rotate the 2nd link 12b about the rotation axis B. The parts 31-33, along with hardware (not shown) for attachment of the disk to the 1st link and the mount to the base, form a kit for outfitting (retrofitting, refurbishment, refitting, or OEM fitting) that robotic arm. Preferably the kit is easily assembled and disassembled, and can be assembled and disassembled many times. Preferably the hardware for attachment (at least to links of the robotic arm) do not require perforation, or any material loss, to avoid weakening the robotic arm and voiding of warranties. Instead band clamps and gripping jaws are preferred for attachment hardware. FIG. 2 depicts a schematic diagram of part of a robotic arm 50 having a series of links 52 connected serially with a base, and an end-effector not shown. FIG. 2 shows an exobrake 70 for splinting an ith joint 54b in a part of a kinematic chain of a robotic arm 50 extending from the i-1th joint 54a, to the i+1th joint 54c, including links 52 (i.e. i-1th link 52a, and the ith link 52b). An end-effector or another link is connected to the i+1th joint 54c, just as the base or another link is connected to the i-1th joint 54a. The i-1th joint 54a controls rotation of the i-1th link 52a about axis C-C, just as the ith joint 54b controls rotation of the ith link 52b about axis about a rotation axis D-D. While 14 typical robotic arms have each joint axis oriented perpendicular to axis of the previous link, FIG. 2 shows the ith link 52b oriented at an angle to this axis. If the robotic arm were to be conventional in this regard: the C and D would be perpendicular. Except for how it affects a working envelope and mechanics of the robotic arm, there is no reason to require that the robotic arm according to the present invention be conventional in this respect, including for the joint splinted by the exobrake, as long as the brake can be mounted coaxially (on either side, or both sides of the splinted joint) and is fixed to rotate with the link arm at either a stator or rotary end, and the opposite link (or base) at the other end to straddle the joint. The robotic arm 50 comprises a exobrake 70 to splint the ith joint 54b. The exobrake 70 also comprises a disk brake with a caliper 71 and disk 72. The disk 72 is rigidly attached to the ith link 52b. The caliper 71 is securely mounted on a caliper mount 73 and positioned so that the disk 72 is between jaws of the caliper 71. The caliper mount 73 is rigidly attached to the i-1th link 52a. The disk 72 rotates with the ith link 52b unless the caliper 71 is actuated to clamp the disk 72, thereby immobilizing the ith joint 54b and the ith link 52b. A motor for rotating the ith link 52b about the rotation axis D-D and attendant electronics (including a controller), gears and the like, are situated in the ith joint 54b. The i-1th joint 54a can house a motor, and attendant electronics (including a controller), gears and the like, for rotating the i-1th link 52a about the rotation axis C-C. Likewise, any of the joints can house motors, attendant electronics (including a controller), gears and the like for rotating a link about a rotation axis. While one exobrake is shown, the robotic arm 50 may comprise another exobrake for splinting one or more of the other joints (whether those shown or others in the robotic arm). FIG. 3 depicts part of a cobot 300 including a base 311, three complete links 312, and one partial link, of a serial kinematic chain between the base 311 and an end (not in view), and four joints 314. The links 312 include a 1st link 312a rotatably connected to the base 311 through a 1st joint embedded in the base 311 (occluded by 1st caliper mount 333). The 1st joint 314a rotates the 1st link 312a about axis E-E. The 1st link 312a couples the 1st joint 314a (elbow shaped) to the 2nd joint 314b, which is a first splinted joint of this example. The 2nd joint 314b (C-shaped) is rigidly connected to the 2nd link 312b, however this link is not in view, as it is covered by the 2nd link 312b in the pose illustrated. The 2nd joint 314b rotates the 2nd link 312b about axis F. The robotic arm of this embodiment is fully conventional in that each link is driven to rotate about its longitudinal axis (i.e. initial segment thereof) and each axis is perpendicular or parallel to the axes of adjacent joints 314. It would be difficult and possibly unhelpful to include other axes, but axis G is partially shown for the 3rd joint and link 312b / 314c, as this link too is splinted. As mentioned hereinabove, the ends (herein rotary or stator) of brakes that are affixed to links (ends affixed to the base can be otherwise mounted) of the robotic arm, can surround the link at one place on the initial segment of the link, or can extend beyond the initial segment. As shown in FIG. 3, the disk 332 is conveniently mounted at a first (90°) bend of the C-shaped second link 312b. Hardware for mounting ends of each brake, in accordance with the present invention, do not affix to more than one link, for otherwise it would preclude normal motion of the robot when brakes are released. The 3rd joint 314c is occluded by the second exobrake (particularly 2nd caliper mount 343) but the 3rd link 312c (elbow shaped) is visible. In both cases the axis of the disk (or other rotary end of the brake) is aligned with the axis of the joint it is splinting, but it can be placed substantially anywhere along this axis. To avoid limiting joint articulation (and therefore range of motion of the cobot), and to provide good support for the rotary end over a wide range of angles, base-distal brake ends are arrayed base-distally of the splinted joint, either surrounding the link, or at bend of the link. In some embodiments, it is difficult or inconvenient to directly couple a brake end to a short link, and instead pairs of passive rotary joints, such as bearing assemblies, can be used to permit coupling to two exobrakes to be mounted by securing to i-1th (or base) and i+1th links without contacting the ith link. Selection of mounting hardware and strategy can be influenced by mechanics of the exobrake, avoidance of self-conflict limitations of the robotic arm, and weight. The 3rd joint 314c is a second splinted joint of the robotic arm. A band of the corresponding exobrake, and the brake itself, occlude part of the 3rd link 312c, except at a distal end. This exobrake has a rotary end positioned to surround the link that it brakes. The 1st exobrake 330 splints the 2nd joint 314b. The 1st exobrake 330 comprises a 1st disk brake having a 1st caliper 331 and 1st disk 332. The 1st disk 332 is rigidly and concentrically attached to 2nd link 312b (orientation of initial segment of the C-shape) by a band 315 that extends around the initial and part of a long midsection of the C-shape, as such the disk 332 is positioned beside a first bend of the 2nd link 312b. The 1st caliper 331 is securely mounted on a 1st caliper mount 333 and positioned so that the 1st disk 332 is between jaws of the 1st caliper 331. The 1st caliper mount 333 is a plate with the 1st caliper 331 located at one end and is rigidly attached to the 1st link 312a at the opposite end thereof fixed to move with the 1st joint 314a. While the 1st caliper mount 333 is shown as if it were a single piece plate, it will be appreciated by those skilled in the art, this design would needlessly complicate assembly. It is far better to provide a plurality of pieces that clamp the link 312 rather than inserting the mount by feeding it through the robotic arm. The stiff plate was chosen for illustration to convey the stiffness of the mount, which is critical because of the distance over which the braking forces are carried. The 1st disk 332 rotates with the 2nd link 312b unless the 1st caliper 331 is actuated to clamp the 1st disk 332 (i.e. the brake is applied), to immobilize the 2nd link 312b, such that the 1st and 2nd links 312 are locked, but these two links can still be swiveled in unison by the 1st joint 314a, even when the brake is applied. The 2nd exobrake 340 splints the 3rd joint 314c, enabling, by application of the brake, the rigid coupling of the 2nd to 3rd links 312. The 2nd exobrake 340 comprises a 2nd caliper 341 mounted via a 2nd caliper mount 343, and a 2nd disk 342 mounted via a band. Two bands are shown, one before and one after the final bend of the C-shaped link 312b. It should be noted that the exobrake 340 as shown can operate equally well whether the disk 342 is affixed to the either band, as long as the caliper 341 is mounted to the other. Given that the weight of the caliper 341 is expected to be greater than that of the disk 342 the caliper is presumed mounted to the local band (distal of final bend), and the disk 342 is affixed proximal of final bend. Thus while it may be more common for the brake’s rotary end to rotate with the rotated link of the splinted joint, it is by no means necessary. FIG. 4 schematically illustrates a compete exoskeleton on a cobot 400. The cobot has a base 411, six links 412 (a-g numbered per convention where visible) connecting the base 411 and an end-effector 413 (i.e. drilling unit) by actuated revolute joints of a serial kinematic chain. The cobot has two long links 412b,c and 4 short links 412a,c,e,f, however the exoskeleton occludes all of the short links, and it is only between rigid struts of the exoskeleton that the two long links can be seen. Nonetheless parts of some of the joints 414 (i.e. 414b,c,d) are in view. Each of the joints is conventional, even if the second joint appears from the viewing plane to be non-perpendicular to the axis of the first link. The cobot 400 is outfitted with a complete exoskeleton 420, including exobrake splints at each joint 414 and mechanical couplings between each exobrake that produce a complete structure extending from the end of the robot to the base 411. A strategy employed for the mechanical couplings is that every long link is coupled by a pair of rigid struts 421 (only one on each labeled for clarity) and complete sheaths 423 (only 3 labeled for clarity) are used for the short links. The pairs of struts 421 extend between adjacent exobrakes of each of the long links 412b,c (struts 421 a connecting exobrakes splinting joint 414b and joint 414c, and struts 421b connecting exobrakes splinting joints 414c to joint 414d. The pairs of struts 421a are located along opposite sides of the respective long link. Each exobrake is provisioned as per the 1st exobrake 430, even if details of the exobrakes are not in view, in most cases. The 1st exobrake 430 comprises a 1st disk brake with a 1st caliper 431 and 1st disk 432. The 1st disk 432 is rigidly attached to a sheath 423 of the 1st link. The 1st caliper 431 is securely mounted on a 1st caliper mount 433 and positioned so that the 1st disk 432 is between jaws of the 1st caliper 431. The 1st caliper mount 433 is rigidly secured to the base 411. The 1st disk 432 rotates with the 1st joint 414a unless the 1st caliper 431 is actuated to clamp the 1st disk 432, thereby immobilizing the 1st joint. This sheath 423 also supplies a second caliper mount for the 2nd exobrake 440, which is positioned to receive a disk of the second exobrake (not in view) within its jaws. Applying the 2nd exobrake 440 prevents rotation of the 2nd joint 414b and therefore the 2nd link 412b, with respect to the first. The long links are similarly provisioned but with struts 421 supplied instead of sheaths 423. In operation, the exoskeleton and cobot 400 can be operated in a number of modes. In one case, the cobot moves into a type B position with all brakes released, giving the robot complete mobility, except for any self-conflict imposed by the exoskeleton itself. Then, once in position, all brakes are simultaneously applied, and the cobot is essentially a single locked end effector, frozen to the base. At this juncture an end effector is applied perform a process that requires no motion of the end of the cobot. In accordance with a variant of this method, once in the B type position, a selected set of joints, such as all joints having a risk of suffering damage during the process, or all joints for which no mobility is required for the type B process, have their brakes applied. Then only those brake-released joints that will be subject to safe loads, can be actuated during the B type process. With reference to FIG. 5A to FIG. 5D, a cobot 500 is illustrated equipped with a drilling end-effector 513 at a distal end of the cobot 500 for drilling into a panel 550, and two exobrakes 530 and 540, which have a unitized structure from the base to the 2nd link of the cobot, and thus define a partial exoskeleton 520. The cobot 500 is of conventional form, with orthogonal axes and joints aligned with these axes, and is not described in detail herein. While joints and links of the cobot are in view, only some of these are labelled (514a-e, and 512a-c). As such the cobot 500 comprises a base 511 at a proxi-mal end of the cobot 500 to support the cobot 500 on a surface of a multi-DoF table 516. Links 512 are cylindrical, and extend between the joints 514 of the serial kinematic chain. The exoskeleton 520 comprises a band 521 for clamping 2nd (C-shaped) link 512b at the proximal end of the long mid-section thereof, as the long mid-section offers more surface area for rigidly securing disk 542 to the cobot 500. The band 521 is rigidly mounted to a shell 525 that surrounds, without contacting, the initial segment of 2nd link 512b and part of the 2nd joint 514b. The shell 525 provides a place to mount a bearing assembly 558, that cooperates with another bearing 557, to avoid clamping of the 1st link 512a. The shell 525 is adapted to surround the 2nd link 512b to be secured by the band 521 so that they collectively affix a bearing assembly 558 to the 2nd link 512b. The stator end of 2nd exobrake 540 and a horseshoe plate 543 are indirectly affixed to the motion of the 1st link 512a via the two bearing assemblies (557,558). The horseshoe plate 543 also serves to affix a disk 532 of 1st exobrake 530. The calipers 531 of the first exobrake 530 are mounted to the base via 1st caliper mount 533. The 1st disk 532 is horizontally oriented and rotates in a horizontal plane about a vertically oriented rotation axis as driven by the 1st joint 514a. The 1st caliper 531 is situated on the 1st caliper mount 533 to receive an outer edge of the 1st disk 532 between the jaws of the 1st caliper 531 external to the 1st joint 514a. Actuation of the 1st caliper 531 closes the jaws of the 1st caliper 531 on the faces of the 1st disk 532 to prevent rotation of the 1st disk 532 thereby affixing 1st joint 514a about the vertical axis, resulting in a freezing of the 1st link 512a and the base 511. The 2nd exobrake 540 comprises 2nd disk 542 affixed to rotate by the 2nd joint 514b with the 2nd link 512b. The 2nd exobrake 540 also comprises a 2nd caliper 541 mounted on a 2nd caliper mount on the horsehoe plate 543. The horseshoe plate 543 is rigidly mounted to a rotor of a bearing (not in view) the stator of which being secured to the base 511. The 2nd disk 542 is vertically oriented and is rotated by 2nd joint 514b with link 512b. The 2nd caliper 541 is situated on the horsehoe plate 543 to receive an outer edge of the 2nd disk 542 between the jaws of the 2nd caliper 541, external to the 2nd joint 514b. Actuation of the 2nd caliper 541 closes the jaws of the 2nd caliper 541 on the faces of the 2nd disk 542 to prevent rotation of the 2nd disk 542 thereby preventing rotation of the 2nd joint 514b, resulting in a stiffening of the cobot. Together, the exobrakes 520 can be used to immobilize and stiffen the cobot 500 for performing drilling work at greater force through the drilling endeffector 513 than the force for which the cobot is rated. FIG. 5C depicts an exploded view of components of the kit for retrofitting the commercial AMTC UR10e collaborative robot. The components shown in FIG. 5C form a kit for outfitting a robotic arm to increase load capacity or improve control thereof, specifically for the 1st and 2nd joints (514a and 514b), of this collaborative robot. At the core of this exobrake is a bearing assembly 557 having an inner raceway 557b and outer raceway 557a. The inner raceway 557b is for mounting to the base of the collaborative robot, directly, or via 1st caliper mount 533. The outer raceway 557b is mounted to rotate with link 512a, without directly mounting thereto. The 1st caliper mount 533 is connected to the base 511 with the 1st caliper 531 affixed thereto. The 1st disk 532 is connected to an underside of the outer raceway 557a which moves with the 1st link 512a driven by the 1st joint 514a. An edge of the 1st disk 532 is positioned between jaws of the 1st caliper 531. The band 521 is provided in two pieces for clamping the 2nd link 512b, serving to affix the sheath 525, the sheath 525 having an elbow shape. The 2nd disk 542 is connected to a bearing nut 552 fitted over a 2nd bearing assembly 514b. The bearing nut 552 is housed in a pillow block 551 fitted to the sheath 525 and a bearing press ring 553 is attached to the pillow block 551 between the pillow block 551 and the 2nd disk 542 to thereby mount the 2nd disk 542 on the 2nd bearing assembly 558 so that rotation of the 2nd joint 514b causes rotation of the 2nd disk 542. The 2nd caliper mount comprises a mounting side 543a of the horseshoe plate 543, that is connected to the outer raceway 557a, the 1st link 512a, and the 1st disk 532. A mounting bracket 543b is for attaching the mounting side 543a to the 2nd caliper 541 proximate the 2nd disk 542. The 2nd caliper 541 is mounted on the mounting bracket 543b such that the edge of the 2nd disk 542 is inserted between the jaws of the 2nd caliper 541. The jaws are separated sufficiently to facilitate proper placement of the 2nd disk 542 between the jaws. A variety of threaded shafts 554 are utilized to bolt the various components together. For added security, a lock nut 555 is provided for one of the threaded shafts 554 to secure the mounting bracket 543b to the mounting plate 543a. FIG. 5D depicts a schematic diagram of a hydraulic system 560 for the exobrakes 530 and 540. The components shown in FIG. 5D are for the 1st exobrake 530. The hydraulic system 560 comprises a three-way valve 561 having a main port 562 through which pressure from pressurized air can be transmitted into the hydraulic system 560. Air may be pressurized in any way known in the art, for example by a pedal-piston arrangement, an air 20 pump and the like. The three-way valve 561 has a 1st port 563 to permit air in an air tube 564 to be pressurized to exert pressure through an air inlet 565 (up to a maximum of about 690 kPa) on a brake fluid (e.g., a glycol ether) contained in the hydraulic system 560. The three-way valve 561 has a 2nd port 566 to permit pressurized air to pressurize brake fluid in the 2nd exobrake 540, which operates the same as or similar to the 1st exobrake 530. Pressure exerted by the pressurized air through the air inlet 565 is exerted on brake fluid in an intensifier 567. The pressure is transmitted from the intensifier 567 through a brake fluid-filled caliper tube 537 (e.g., a metal tube) into the 1st caliper 531 thereby causing the jaws of the 1st caliper 531 to close on the 1st disk 532 (not seen in FIG. 5D) thereby preventing rotation of the 1st disk 532. The 1st caliper 531 is equipped with bleeder valves 536 for removing air from brake fluid from the 1st caliper 531, when needed. In fluid communication with the intensifier 567 is a brake fluid reservoir 568 that contains a supply of brake fluid to ensure that the hydraulic system 560 contains sufficient brake fluid. Brake fluid in the reservoir 568 can freely flow into the intensifier 567 through a check valve 569, which is mounted vertically to permit gravity feed of brake fluid from the reservoir 568 into the intensifier 567. The check valve 569 permits fluid flow only in one direction from the reservoir 568 to the intensifier 567. Control of the exobrakes 530 and 540 through the hydraulic system 560 was tied to the control system of the commercial AMTC UR10e collaborative robot. Simple input / output (I / O) logic was implemented in a switch to the switch the hydraulic system 560 on and off to actuate or deactivate the exobrakes 530 and 540 simultaneously. However, two switches could be provided, one for each exobrake, if desired. FIG. 6 a flow chart showing a process for drilling into a panel utilizing a cobot of the present invention. In step 1 601, the cobot moves to the drilling pose while all brakes are released, allowing the exobrakes to passively follow 602. Once at the drilling pose, the cobot normalizes the drilling head 603 and docks on a panel 605. The exobrake of the cobot is then activated 606 to immobilize and stiffen the cobot. Any (free) joints of the cobot can then be selectively activated to improve the drilling process, and those joints that are immobilized are left in a free-driving mode 607 as any attempted actuation of these joints would simply fight the brake. The end-effector builds the clamping force and drilling is commenced in accordance with pre-programmed responsive instructions (smart drilling) 610. The exobrakes support the clamping and drilling forces generated by the drill. Once the drilling is complete, the exobrake of the cobot is deactivated 612 and the cobot is moved to another task. While this example is specific to cobotic drilling, it will be appreciated that other A / B processes can be used equally. Examples The exoskeleton 520 of FIGs. 5A-C was fabricated, and coupled with a hydraulic system of FIG. 5D. The parts were all formed of steel, as custom manufactures. The kit was assembled and mounted on a commercial AMTC UR10e robot to provide braking of motion about rotational axes of 1st joint 514a and 2nd joint 514b. A drilling end-effector 513 capable of applying a force of up to 45 kg, capable of sensing the applied force, capable of triggering the drilling process, and capable of detecting the end of drilling cycles was manufactured and attached to the cobot 500. Dynamic test results using the cobot 500 are shown in FIG. 7, FIG. 8 and FIG. 9. FIG. 7 depicts a graph of angular position of a 1st joint (qi, radians) of the cobot vs. time (ms) showing the deviation of the joint from a target position (plot T1) when the cobot has the exobrake engaged (plot E1) and disengaged (plot D1). At 200 ms (point S1) in FIG. 7, the angular position of the 1st joint of the cobot with the exobrake disengaged because it deviated by about 3.5° from the target position which is a provisioned limit at which time the cobot stopped operating and issued a warning alarm. FIG. 8 depicts a graph of force (N) vs. time (ms) showing the clamping force that the cobot can apply with (plot E2) and without (plot D2) the exobrake engaged. With the exobrake engaged (plot E2), the cobot reaches an assigned clamping force of 60 N and finishes the drilling task. Without the exobrake engaged (plot D2), the cobot stopped operating and issued a warning alarm after 200 ms while reaching a clamping force of only 30 N with the 3.5° deviation of the 1st joint from the target position. FIG. 9 depicts a graph of real angular speed (deg / sec) vs. commanded angular speed (deg / sec) of the end of the cobot without the partial exoskeleton 520 mounted to the cobot, and with the partial exoskeleton 520 mounted to the cobot, in order to compare the performance of the robot before and after the addition of exobrake masses. The small degree of loss of responsiveness of the cobot were expected given the increase in inertia provided by the partial exoskeleton 520, but are a small price to pay for enabling high 22 payload capacity processes of the A / B type. FIG. 9 shows that the velocity of the cobot is only minimally slower when the exobrake is passively following (plot E3) than when the exobrake is not on the cobot (plot D3). Further tests were conducted by commanding the first two joints (base and shoulder) individually to move with different angular velocities. The comparison shows that the first joint (base) can achieve the commanded angular velocity of the native cobot by applying up to 30% more current at higher velocities. The second joint (shoulder) maintains the current unchanged regardless of whether the partial exoskeleton is mounted or not, but it experiences a 35% decrease in velocity during very high-speed motion. Since the tool-center point motion is a combination of all joints, the decrease in angular velocity of the second joint will only affect a small proportion of the total motion. It is also important to mention that the angular velocity is comparable in both cases up to 50 deg / sec, which is considered high velocity, and it is rare for the second joint to be tasked with very high-speed movements in many A / B processes and in manufacturing operations in general. The data demonstrated that the addition of the partial exoskeleton 520 dramatically increased the clamping force that the cobot 500 could exert, but did not significantly influence the programmed velocity in common working speeds of the cobot 500. However, in other tests, the current drawn by motion of the cobot 500 increased by up to 20%. The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.

Claims

1. A kit for outfitting a robotic arm to increase payload capacity or improve control thereof, the robotic arm having a base, an end, and a serial kinematic chain of actuated, jointed links from the base to the end, the kit comprising:a brake having a stator end and a rotary end; andmounting hardware for securing the stator end and the rotary end to the robotic arm to straddle a first revolute joint of the robotic arm, the mounting hardware comprising at least one tensioning brace that at least partially surrounds the link to secure the end of brake to that link without perforating or penetrating the link;wherein: the stator and rotary ends, and mounting hardware are configurable to form a brake that reinforces the first joint when assembled, whereby applying brakes to the mounted assembly stiffens the robotic arm by providing a splint for the first joint, in at least one disposed angle of the first joint.

2. A kit for outfitting a robotic arm to increase payload capacity or improve control thereof, the robotic arm having a base, an end, and a serial kinematic chain of actuated, jointed links from the base to the end, the kit comprising:at least two brakes, each brake having a stator end and a rotary end;mounting hardware for securing the stator end and the rotary end of each brake to the robotic arm to straddle respective revolute joints of the robotic arm, where:these respective revolute joints are sequential joints of the robotic arm such that, when assembled, a single link secures two ends of two of the brakes; andthe stator and rotary ends, and mounting hardware are configurable to form two exobrakes that reinforce the sequential joints when assembled, whereby applying brakes to the mounted assembly stiffens the robotic arm by providing respective splints in at least one disposed angle of each of the sequential joints; andthe mounting hardware for securing respective ends of the two brakes to the single link are unified, to form an exostructure that splints the two respective joints and reinforces the single link.

3. The kit of any one of claims 1 or 2 further comprising an electrically controlled pneumatic, hydraulic, or mechanical actuation and release system for the brakes.

4. The kit of claim 3 wherein at least one of the electrical control of the actuation and release system, or a pneumatic, or hydraulic line thereof, is adapted to couple to a service24port the robotic arm or an end effector thereon, whereby the robotic arm, or a process controller of the end effector, is adapted to control braking.

5. The kit of any one of claims 1 to 4 wherein the rotary end comprises one of: a brake disk; a brake drum; and a brake cone, or a sector part thereof, and the stator end comprises a mover of a brake pad for moving the brake pad into and out of contact with the rotary end.

6. The kit any one of claims 1 to 5 wherein the mounting hardware is configured to:affix a first of the brake ends for movement with a base proximal link, or base, of the robotic arm, and affix a second of the brake ends for movement with a base distal link of the robotic arm, in each case the respective brake end being affixed by: clamping the respective links, or clamping one of the brake ends to an adjacent link and interposing two free revolute joints between clamps for clamping the ends;secure the rotary end base distally of the first joint, and the stator end base proximally of the first joint, especially if the rotary end is lighter than the stator end.

7. The kit of any one of claims 1 to 6 wherein the exobrake further comprises at least one sensor for determining an actuation condition of the brake.

8. The kit of any one of claims 1 to 7, except when dependent on claim 3, further comprising software for adapting a processor for controlling the robotic arm to: determine when a brake is mounted at the first joint; determine when the brake at the first joint is under the control of the controller; determine a state of actuation of the brake at the first joint; or prevent a command to change an angular disposition of the first joint when the brake is applied.

9. The kit of any one of claims 1 to 8 wherein the first joint is the 1st, 2nd, or 3rd joint of the robotic arm.

10. The kit of claim 9 wherein the first joint is:the 1st joint in that the stator end is secured to the base of the robotic arm, and the rotary end is secured to the 1st link of the robotic arm; orthe 2nd joint in that the stator end is secured to the 1st link of the robotic arm, and the rotary end is secured to the 2nd link of the robotic arm.

11. The kit of any one of claims 2 to 10, except when dependent on claim 1, wherein the mounting hardware comprises: at least one tensioning brace that at least partially25surrounds the link to secure the end of brake to that link without perforating or penetrating the link.

12. The kit of any one of claim 1 to 11, wherein the mounting hardware comprises a set of parts that admits of multiple configurations to allow the brake to splint two or more joints of one or more models of robotic arm; or at least 3, and preferably 5 shims for independent precision alignment of the rotor end with respect to the stator end.

13. The kit of claim 1 or any one of claims 3 to 12, except when dependent on claim 2, further comprising a plurality of instances of the brakes and mounting hardware, each configured for mounting to straddle a different respective first joint of the robotic arm, to, when mounted with brakes applied, provide splints for each of the respective first joints.

14. The kit of claim 13 where two of the respective first joints of the robotic arm are adjacent in the serial kinematic chain, such that, when assembled, a single link secures two ends of two of the brakes, and at least one piece of the mounting hardware for each of these two ends is unified in that the splints are rigidly coupled when assembled to form an exostructure that splints the two of the respective first joints and further reinforces the single link.

15. The kit of claim 14 where the two of the respective first joints are the 1st and 2nd joints of the robotic arm, and thus the exostructure is an exoskeleton that reinforces the robotic arm when assembled, from the base to at least the 2nd joint.

16. The kit of any one of claims 1 to 15 assembled and mounted on the robotic arm.

17. The assembly of claim 16 wherein the robotic arm is: a human-safe robot, a cobot, or a robot with: a contact sensor for detecting and mitigating collision; and velocity and torque limitations rated to reduce damage from collision.

18. The assembly of claim 16 or 17 further comprising a soft wrap outer envelope that extends over the robot and the assembly to reduce damage from anticipated collisions with a class of bodies, the class possibly being humans, or humans with certain protective equipment.

19. A method of augmenting payload capacity of a robotic arm, the method comprising:adding to the robotic arm an exostructure to first and second sequential revolute joints of the robotic arm; and,controlling the exostructure to:allow the rotary end to move freely when the first and second joints are actuated5 and the brakes are not engaged; andapply contact between the rotary end and stator end of the brakes to resist rotation of the first joint when the brakes are engaged.

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