Intrinsically safe lightweight dexterous torque controlled robotic manipulator

Abstract

A robotic arm design, also referred to as Maestro is provided, which is a compact torque controlled manipulator tailored for compliant and safe physical interaction in human-shared spaces. Maestro integrates four design innovations: a singularity-free wrist with three intersecting axes, a lightweight arm minimizing inertia, a modular joint unit for torque control, and a novel reconfigurable joint limit module for enforcing hardware-level workspace constraints. These structural and actuation-level innovations collectively enable compliant, predictable behavior with intrinsic safety.

Description

[0001] INTRINSICALLY SAFE LIGHTWEIGHT DEXTEROUS TORQUE CONTROLLED ROBOTIC MANIPULATOR

[0002] FIELD OF THE INVENTION

[0003] This invention relates to robotic manipulators.

[0004] BACKGROUND OF THE INVENTION

[0005] A long-standing goal in robotic manipulation has been to enable robots to interact physically with humans in a way that is not only precise and compliant, but also inherently safe. As robots increasingly enter human-shared environments — public spaces, hospitals, homes — new constraints arise: they must minimize injury risk during contact, operate smoothly in tight spaces, and avoid intrusive or unpredictable full-body movements. These requirements call for manipulators with low reflected inertia, compliant and precise force control, efficient and predictable operation, and localized motion behavior.

[0006] Torque-controlled manipulators provide a strong foundation for addressing many of these demands. By directly controlling joint torques, these robots can modulate contact forces in realtime, enabling compliant and safe interaction with their environment. Additionally, high- bandwidth torque control effectively reduces reflected inertia by compensating for the amplification effects of gears and actuator shaft inertia — where reflected inertia scales with the square of the gear ratio (q2). This reduction in reflected inertia minimizes impact forces during unintended collisions, enhancing operational safety. However, as manipulation tasks move into increasingly unstructured and human-centric spaces, it becomes essential not only to have compliant force control but also to enforce safety at the structural level. Given that torque control ultimately operates through software, supplementing it with mechanical constraints at the workspace level can provide a useful additional safeguard.

[0007] Over the past decades, numerous manipulator designs have explored optimal kinematic and dynamic configurations. Design features such as intersecting roll-pitch-yaw axes with compact wrist, explicit joint torque sensing, dual encoders on both motor and link sides, and lightweight yet stiff structural architectures have been shown to improve kinematic and dynamic performance and safety. However, to date, torque-controlled manipulators have been unable to integrate all these features into a cohesive design. The present invention addresses this gap.

[0008] SUMMARY OF THE INVENTION

[0009] The present invention provides a robotic arm design. The robotic arm design is characterized by a wrist that is configured as follows (see FIG. 12 for references to joints). The wrist has a first joint module (referred to as joint 5) with a first revolute joint having a first axis for roll, a first input link, a first output link, a first torque sensor, a first motor side encoder, a first output link side encoder, and a first motor. The wrist has a second joint module (referred to as joint 6) with a second revolute joint having a second axis for pitch, a second input link, a second output link, a second torque sensor, a second motor side encoder, a second output link side encoder and a second motor. The wrist has a third joint module (referred to as joint 7) with a third revolute joint having a third axis for yaw, a third input link, a third output link, a third torque sensor, a third motor side encoder, a third output link side encoder and a third motor. In this design, the first axis, the second axis and the third axis nominally intersect at substantially a single point with a design tolerance and are arranged in a roll-pitch-yaw singularity free joint arrangement. In one example, the design tolerance is up to 25 mm.

[0010] Further in this design, referring to FIG. 12, joint 6 for pitch, the output of the second torque sensor is attached and grounded to the second input link, and the second motor is attached to and rotating with the second output link.

[0011] Further in this design, referring to FIG. 12, joint 7 for yaw, the output of the third torque sensor is attached and rotating with the third output link, and the third motor is attached to and grounded to the second output link. The first axis and the second axis are mutually orthogonal and intersecting and the second axis and the third axis are mutually orthogonal and intersecting.

[0012] The robotic arm design further has an arm proximal to the wrist, where the arm has four joint modules each having revolute joints, and where all joint frames of the arm are colinear with no offsets from each other. The third axis and a fourth axis of one of the four joint modules of the arm are mutually orthogonal and intersecting.

[0013] In a further embodiment of the robotic arm design, the first joint module, the second joint module, the third joint module and the four joint modules of the arm each have joint limiter module capable of configuring a bidirectional range of motion of the respective joint module and therewith reconfigure the reachable workspace of the robotic arm. Additional characteristics are, for example, that each of the wrist joints also has a motor (input) and link (outside) side high resolution encoders, which enables high resolution BLDC commutation and high bandwidth torque control. To preserve compactness of the joint module, both the encoders have been placed on the same side.

[0014] The robotic arm design, also referred to as Maestro is a compact torque-controlled manipulator tailored for compliant and safe physical interaction in human-shared spaces. Maestro integrates four design innovations: a singularity-free wrist with three intersecting axes, a lightweight arm minimizing inertia, a modular joint unit for torque control, and a novel reconfigurable joint limit module for enforcing hardware-level workspace constraints. These structural and actuation-level innovations collectively enable compliant, predictable behavior with intrinsic safety.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 shows according to an exemplary embodiment of the invention a comparison between the arm design of the present invention versus the Kuka iiwa robotic arm design.

[0017] FIG. 2 shows according to an exemplary embodiment of the invention the robotic arm design referred to as the Maestro arm design.

[0018] FIG. 3 shows according to an exemplary embodiment of the invention a comparison of the wrist designs of Maestro (left, according to the present invention) and the Franka Panda design (right).

[0019] FIG. 4 shows according to an exemplary embodiment of the invention a coplanar arrangement of the joint frames of the robotic arm design.

[0020] FIGs. 5A-C show according to exemplary embodiments of the invention assembled arm components: (FIG. 5A) Wrist assembly with integrated pitch and yaw joints. (FIG. 5B) Joint module assembly. (FIG. 5C) Link and joint module assembly.

[0021] FIGs. 6A-B shows according to exemplary embodiments of the invention (FIG. 6A) Reconfigurable joint limit module (RJLM) and (FIG. 6B) section view of a full link-joint assembly.

[0022] FIGs. 7A-D show according to exemplary embodiments of the invention a comparison of wrist motion in Panda (FIG. 7A) and Maestro (FIG. 7B) while following a horizontal trajectory with fixed end-effector orientation. (FIG. 7C), (FIG. 7D) Jacobian condition numbers computed along the trajectory.

[0023] FIGs. 8A-C show according to exemplary embodiments of the invention end-effector orientation control about a fixed position using (FIG. 8A) Panda and (FIG. 8B) Maestro. Joint angle deviations from nominal posture are shown in (FIG. 8C).

[0024] FIG. 9 shows according to an exemplary embodiment of the invention a comparison of effective mass distribution using belted ellipsoids for Panda (left) and Maestro (right, according to the robotic arm design of this invention).

[0025] FIGs. 10A-B show according to exemplary embodiments of the invention (FIG. 10A) presents the predefined task-workspace (1010) and the prohibited zones (1020). (FIG. 10B) contrasts the original (1030) and the reconfigured (1040) workspaces, illustrating how the system adapts to task-specific constraints for an ultrasound scanning application. The results were obtained through simulation in OpenSAI.

[0026] FIG. 11 shows according to an exemplary embodiment of the invention the robotic arm design.

[0027] FIG. 12 shows according to an exemplary embodiment of the invention the wrist design of the robotic arm design. FIG. 13 shows according to an exemplary embodiment of the invention the wrist design configuration of the robotic arm design.

[0028] FIGs. 14A-D show according to exemplary embodiments of the invention as referred to in FIGs 11-12, (FIG. 14A) joint 6 arrangement, (FIG. 14B) joint 6 component assembly, (FIG. 14C) joint 7 arrangement, and (FIG. 14D) joint 7 component assembly.

[0029] FIG. 15 shows according to an exemplary embodiment of the invention intersecting wrist axes, i.e. joints 5, 6, and 7.

[0030] FIG. 16 shows according to an exemplary embodiment of the invention intersecting wrist with 90 degrees output flange.

[0031] FIG. 17 shows according to an exemplary embodiment of the invention wrist in nonsingular configuration in the middle of the wrist workspace (left) versus singular configuration at the boundary of the wrist workspace (right).

[0032] FIG. 18 shows according to an exemplary embodiment of the invention integrated joint limiter modules at joints 1-4.

[0033] FIG. 19 shows according to an exemplary embodiment of the invention coplanar design of joint frames.

[0034] FIG. 20 shows according to an exemplary embodiment of the invention a joint module arrangement in the link.

[0035] FIG. 21 shows according to an exemplary embodiment of the invention a joint module component assembly which is used on joints 1-5 .

[0036] FIG. 22 shows according to an exemplary embodiment of the invention the joint 6 component assembly.

[0037] FIG. 23 shows according to an exemplary embodiment of the invention the joint 7 component assembly.

[0038] DETAILED DESCRIPTION

[0039] Definitions

[0040] Revolute Joint - A revolute joint (e.g. a pin joint or a hinge joint) is a one degree-of-freedom kinematic pair used in mechanisms. Revolute joints provide single-axis rotation function.

[0041] Explicit Torque Sensing - Torque sensor at each joint that enables torque control so the output link has a pure torque source and the non-linear effects of gear, bearings and other transmission elements can be removed.

[0042] Description of Embodiment

[0043] To address the gap in the art of torque-controlled manipulators the present invention focuses on integration all certain features into a cohesive design. The inventors called the design Maestro — a novel torque-controlled manipulator that integrates high-performance design attributes into a unified platform with an added layer of mechanical safety. Maestro features a singularity-free wrist, a compact and lightweight structure, dynamic decoupling, and inherent task-specific workspace constraints, with kinematics and dynamics optimized for safe, efficient operation. FIG. 1 shows the Maestro arm in comparison with the Kuka iiwa 14.

[0044] Substantial progress has been made in the development of torque-controlled manipulator design, especially in contrast to traditional industrial position-controlled arms. These conventional systems often rely on high gear ratios, which introduce nonlinear behavior, dynamic coupling, and high output impedance, resulting in non-compliant behavior that makes them poorly suited — and potentially unsafe — for operation in unstructured or human-shared environments.

[0045] In recent years, the development of torque-controlled manipulators has demonstrated impressive control capabilities, including high-fidelity torque tracking, low output impedance, dynamic decoupling, and high control bandwidth at the joint level. These capabilities have enabled unified motion and force control, and more importantly, safe physical contact interaction. Most existing torque-controlled arms, however, are designed for general -purpose use, emphasizing large payloads, extended workspaces, and versatile task coverage. Adapting such systems to compact, human-shared environments requires additional design considerations.

[0046] First, many current platforms are physically large with heavy link structure, resulting in high reflected inertia that increases the risk of injury upon contact.

[0047] Second, their wrist joints exhibit large coupling between end-effector orientation and proximal joint motion. This causes small orientation changes to require large arm motions, resulting in workspace inefficiency and potential safety concerns.

[0048] Third, singularity during task execution when two or more of the joints of a serial manipulator are axis-aligned. These singularities degrade controllability and can lead to unstable behavior, posing additional safety concerns in close-proximity tasks.

[0049] Fourth, in general -purpose manipulators, unconstrained joint motion supports versatility and broad task coverage. However, this extensive reach can become a liability in tasks confined to smaller, human-shared spaces. Although torque control enables dynamic compliance and minimizes reflected inertia, it does not impose physical constraints on the robot’s reachable configuration space. In the absence of hardware-level workspace bounding, faults or unanticipated behaviors in software-based controllers may result in the robot entering unsafe or collision-prone areas. Several torque- controlled robotic platforms have significantly advanced the field of compliant manipulation, each contributing unique architectural and control features suited to their intended applications.

[0050] The Artisan project, developed at Stanford Robotics Lab, demonstrated success in high- bandwidth torque control with modular and compliant actuation. It laid the groundwork for future research in low-impedance physical interaction. The DLR Lightweight Robot (LWR) and its commercial successor, the KUKA iiwa, introduced sophisticated joint impedance control and brought torque-controlled compliance to industrial contexts, supporting large workspaces and payloads. The Franka Emika Panda made such technologies more accessible through a compact, cost-effective platform, while the Flexiv Rizon explored adaptive impedance for unstructured environments.

[0051] While these platforms offer strong performance across a broad range of tasks, their designs remain rooted in general-purpose versatility. Their design priorities differ from those required for human-contact-oriented manipulation, where touch safety, localized interaction, and delicate task execution are critical.

[0052] Maestro Design Methodology

[0053] The arm design process began with defining the payload capacity and task space requirements. A preliminary kinematic model of the manipulator was developed to analyze the torque and motion profiles at each joint under a variety of tasks involving a 3 kg payload. These analyses informed the selection of appropriate actuator and gear combinations capable of satisfying the performance criteria.

[0054] Next, the kinematic structure was optimized to incorporate a non-singular wrist design with three intersecting rotational axes. Following this, the mechatronic and structural aspects were developed, resulting in a feasible and compact wrist design. With the wrist finalized, the remaining arm segments were designed to fulfill the overall task specifications. Actuator placement and structural configuration were determined through dynamic optimization, with the goal of maximizing operational space accelerations. This was achieved by minimizing reflected inertia and optimizing the projection of joint torques into the task space.

[0055] To support modularity, the arm was designed with distinct link and joint modules to facilitate ease of manufacturing, integration, calibration, and maintenance. Additionally, a Reconfigurable Joint Limit Module (RJLM) was incorporated into joint-link interface. This mechanical subsystem enforces physical constraints on joint motion, providing task-specific workspace safety and augmenting overall system robustness.

[0056] Wrist Design

[0057] The key design objectives for the wrist were: (1) a roll-pitch-yaw joint configuration, (2) intersecting joint axes, and (3) minimal distance from the wrist center (i.e., the intersection point of the three axes) to the end-effector. The roll-pitch-yaw arrangement eliminates internal wrist singularities encountered in roll-pitch-roll configurations within the usable workspace, while intersecting axes and a short moment arm reduce kinematic coupling between orientation and position control.

[0058] Designing a compact, torque-controlled wrist with these characteristics introduces significant mechatronic challenges. High-bandwidth torque control requires each joint to be equipped with an integrated torque sensor, a high dynamic-response brushless DC (BLDC) motor, and a wave strain gear to provide torque amplification. To accurately capture joint flexibility and enable precise control, high-resolution encoders were incorporated on both the motor (input) and link (output) sides of each joint.

[0059] To meet these requirements within a compact form factor, actuator placement was optimized through an interlocked configuration of the pitch and yaw actuators. This was achieved by mechanically grounding the pitch torque sensor to the preceding link, as shown in FIG. 2. The final design, shown in FIG. 3, results in an ultra-compact and light-weight wrist with approximately a 50% reduction in moment arm length compared to the Franka Panda arm, while preserving torque sensing accuracy and high-fidelity control performance.

[0060] Arm Design

[0061] The ultra-compact and lightweight wrist enables the design of the rest of the arm with significantly lower loading requirements. This reduction in joint and structural loads relaxes the overall stiffness constraints, facilitating a more compact and lightweight arm design.

[0062] To simplify the kinematics, the shoulder — comprising of the first three proximal joints — is configured in a roll-pitch-roll arrangement with intersecting axes. Joint 4, serving as the elbow, introduces an additional pitch degree of freedom. This structure leads to a full 7-DoF arm when integrated with the 3-DoF intersecting-axis spherical wrist. To further reduce kinematic coupling, the arm is designed such that each joint frame lies on a common plane, as shown in FIG. 4

[0063] Dynamic optimization was employed to determine the placement of joints, joint modules within each link, and overall link lengths. The objective was to maximize linear and angular accelerations in operational space within a specified task workspace. This analysis led to the proximal placement of joint and joint modules within each link and an optimized location for the elbow joint to improve dynamic performance.

[0064] Modular Design

[0065] To support modularity and ease manufacturing, integration, calibration, and maintenance, the arm design is divided into two primary components: link modules and joint modules. Each link module has a structural exoskeleton that defines the manipulator’s kinematic geometry and provides the necessary structural stiffness for payload handling. An integrated cross-roller bearing at each link interface supports load transfer and enables smooth, single-degree-of- freedom rotational motion. The joint module houses all actuation, transmission, and sensing components required for high-bandwidth torque control. Each joint module integrates a brushless DC motor, a strain wave gear for compact and high-ratio reduction, and an output-side torque sensor. Encoders are placed on both the motor (input) and link (output) sides to enable precise torque and position control. FIG. 6B shows a cross-sectional view of the integrated link and joint module showing the internal component layout and integration strategy. Component Assembly

[0066] To validate the design feasibility, the primary building blocks of the arm — namely the wrist module, joint module, and a joint-link module — were fully assembled. The wrist module, shown in FIG. 5A, integrates both pitch and yaw joints along with their corresponding actuation and sensing components. Actuator control and encoder calibration were performed to verify functionality. Similarly, the joint module in FIG. 5B and the joint-link assembly in FIG. 5C were also completed, with actuator and sensor calibration carried out for both. These fully assembled and tested components confirm the design feasibility of the Maestro arm.

[0067] Intrinsic Safety Design

[0068] Recognizing that software-based safety remains inherently fallible due to potential sensor malfunctions, control errors, or unpredictable external disturbances, Maestro adopts a design philosophy that integrates hardware-level safety mechanisms to provide an additional layer of protection through intrinsic, physically enforced constraints.

[0069] To this end, Maestro incorporates a novel mechanical safety device: the Reconfigurable Joint Limit Module (RJLM), shown in FIGs. 6A-B. The RJLM is a compact, modular mechanism that mounts directly onto the joint actuator and enforces configurable upper and lower joint limits via a passive, ratchet-based mechanism. It is electrically isolated from the robot’s main control circuitry and remains entirely unpowered during operation. Once configured, the RJLM serves as a purely physical constraint, intrinsically limiting joint motion independent of the control system.

[0070] In the Maestro arm, RJLMs are deployed on the first four proximal joints. These joints define the wrist point position and thereby determine the primary task-space envelope, while the distal wrist joint extends the orientation range within that space. Moreover, the proximal joints and their associated links contribute the majority of the robot’s mass, inertia, and torque capacity, making hardware-constrained safety particularly critical.

[0071] Maestro Arm Characteristics

[0072] This section details the key performance characteristics of the Maestro arm that emerge from its mechanical and kinematic design. Maestro incorporates a singularity-free wrist, intersecting joint axes, and reconfigurable joint limit modules within a compact and lightweight structure. The inventors present here comparative analyses with an existing torque-controlled manipulator to examine singularity robustness, position-orientation decoupling, and effective mass. Also, workspace reshaping of the Maestro arm is demonstrated using joint-level mechanical constraints implemented by the Reconfigurable Joint Limit Module (RJLM), which can be tuned to enforce task-specific spatial boundaries.

[0073] Wrist Singularity

[0074] To evaluate the singularity robustness of the Maestro arm, the inventors conducted a comparative analysis against the Franka Panda, which features a conventional roll-pitch-roll wrist configuration. Both robots were tested under constrained operational-space control, executing a pure horizontal translation of the end-effector from Pstart to Pend, while maintaining a fixed orientation. To simulate near-singular configurations, the nominal postures were chosen such that joint 1 and joint 3 axes are approximately coaxial and the wrist is in full horizontal extension. FIGs. 7A-D illustrate the difference in wrist joint behavior during the same trajectory. The Panda in FIG. 7A exhibits significant rotational motion in its distal joints, accompanied by unstable whole-body movement. In contrast, the Maestro wrist in FIG. 7B maintains stable motion with minimal wrist joint displacement.

[0075] To quantify this behavior, the condition number (K) of the Jacobian matrix was computed along the trajectory. As shown in FIG. 7C, the Panda’s condition number shows a sharp rise indicating proximity to a singularity, while the Maestro remains stable throughout, demonstrating the effectiveness of its singularity-free wrist design.

[0076] Linear-Angular Motion Characteristics

[0077] The Maestro wrist design features a shorter moment arm, intersecting wrist axes, and a coplanar joint frame arrangement. These characteristics contribute to improved decoupling between orientation and position control. The wrist joints are solely responsible for orientation control, which occurs purely about the wrist point, while the proximal joints (joints 1 through 4) determine the position of this point. Because the wrist moment arm is deliberately minimized by design, orientation control induces minimal deviation in the proximal joints.

[0078] Noted is that the moment arm for the proposed wrist is nominally at 66.5 mm. It is difficult to make an exact number as it can be further reduced if one would use different components in similar wrist pitch and yaw joint arrangement. For the purposes of this invention it is important to note that this arrangement of joints enables one to achieve all three characteristics: compactness, intersecting, and roll-pitch-yaw configuration which is not possible with existing designs. To quantify compactness as per this invention, one could say at a maximum of 66.5 mm nominally.

[0079] To evaluate this decoupling performance, a comparative analysis was conducted against the Franka Panda, which has a comparable overall arm length. In both robots, the end-effector was held fixed at an identical position in operational space while its orientation was rotated about the Y-axis through an equivalent range, as shown in Figure 8. The resulting deviations in the proximal joint angles (joints 1-4) were measured relative to their nominal configuration.

[0080] The results indicate that joints 2 and 4 — primarily responsible for positioning the wrist — exhibit significantly larger deviations in the Panda arm compared to the Maestro, highlighting the latter’s superior decoupling between orientation and position control.

[0081] Effective Mass

[0082] To evaluate the lightweight design of Maestro, we compare its effective mass against that of the Franka Panda, which has a similar payload capacity of 3 kg. Generally, achieving higher payload capacity requires larger and more robust mechanical structures, inevitably increasing the overall robot mass and inertia. Therefore, comparing two manipulators with equivalent payloads allows assessment of how much lower Maestro’s effective mass is relative to Panda, for the same performance capability. To visualize and quantify the directional mass distribution of each robot, the belted ellipsoid representation is employed, which captures the effective mass of a manipulator along all directions.

[0083] As shown in FIG. 9, both manipulators were placed in similar configurations and evaluated using identically scaled belted ellipsoids in simulation. Maestro exhibited significantly smaller ellipsoids overall, with average principal lengths of approximately 4.6 kg and 1.6 kg along its major and minor axes, respectively. In contrast, the Panda’s ellipsoids showed substantially larger values, 9.3 kg and 4.7 kg. This indicates that Maestro possesses substantially lower effective mass relative to its payload, making it better suited for safe, low-impedance motion in human-shared environments.

[0084] Workspace Reshaping with Reconfigurable Joint Limit Modules

[0085] To reconfigure the robot’s workspace for a specified task, the task-workspace is initially defined as the area within which the end-effector must operate, while concurrently identifying prohibited regions, areas that must be avoided due to safety constraints. The objective is to design the robot’s reachable workspace to completely encompass the task region, while preventing entry into prohibited zones.

[0086] However, since RJLMs impose constraints on joint motion through fixed mechanical limits at each joint, the resultant reachable workspace cannot be precisely tailored to fit arbitrary taskworkspace boundaries, particularly those that are flat or convex. To address this limitation, a task-specific penetration tolerance is established, and the joint limit configuration is optimized to better approximate the desired workspace within this acceptable margin.

[0087] FIGs. 10A-B show a representative case in which the robot conducts an ultrasound scanning task on a patient’s abdomen. The task workspace includes the region in direct contact with the abdomen, permitting for a few centimeters of penetration. Prohibited spaces include the remaining body volume and surrounding aisles accessible to bystanders. Given the positions of the subject, the environment, and the robot, the resulting reshaped workspace that satisfies these constraints is illustrated in 1040 in FIG. 10B. While the original full-range workspace, shown in red, completely penetrates the subjects and the aisle, the reshaped workspace effectively avoids them. When the robot base position is adjustable relative to the subject, a broader set of joint limit combinations becomes feasible for workspace adaptation.

[0088] Alternate Description of the Embodiment

[0089] In another embodiment, the invention can be described as a novel intrinsically safe light-weight dexterous torque controlled robotic manipulator.

[0090] In one embodiment, the manipulator is a 7 degrees of freedom torque controlled robotic arm with each degree of freedom comprising of a revolute joint. The arm is designed as a serial kinematic structure with explicit torque sensing at each joint. FIG. 11 shows the robotic arm design with the specific joints, whereas FIG. 12 shows the wrist design of the robotic arm with the specific joint configuration.

[0091] Key features of the design are:

[0092] 1. Wrist design:

[0093] Wrist of a robotic manipulator is made of the last three joints i.e. joints 5, 6 and 7 and is designed to primarily control the orientation of the end-effector. Wrist design plays a critical role in the design of the entire robotic arm. Due to the serial kinematic chain of the arm, each joint carries the load of succeeding joints and links. Therefore, if the wrist is heavy and bulky, then the joints preceding the wrist will have larger output torque requirement and the links will be larger and heavier to achieve sufficient stiffness.

[0094] Ultra-compact lightweight wrist design:

[0095] Larger wrist also means large moment arm which is offset from the wrist point to the endeffector point (FIG. 3). Having large moment arm would increase the torque requirements for the joints. Another problem with large moment arm is that the wrist point has a large deflection during reorientation of the operational point. This large deflection must be accommodated by joints that control the position of the wrist point. Thus, there is large deflection of the joints from nominal position during reorientation task. This makes reorientation tasks inefficient. Therefore, to achieve a lightweight and compact robotic arm with improved kinematics we have designed a lightweight and compact wrist shown in FIGs. 14A-D.

[0096] The wrist according to this invention is designed to carry a payload of 3kg which is comparable to Franka Panda (3kg) and Kinova Gen 3 (4kg) robotic arms. To have comparable payload within a compact form factor, detailed analysis of both static and dynamic torque requirements was carried out in simulation.

[0097] A comparison (FIG. 3) was made between the arm’s wrist of this invention to end-effector point offset i.e. the moment arm and Franka Panda wrist moment arms. The wrist design’s moment arm of this invention is approximately 50% smaller than Franka Panda’s wrists respectively. This reduction has been possible due to ultra-compact arrangement of the wrist joints and components (FIG. 3).

[0098] To get a compact wrist, we have used a hybrid joint-link design wherein the joint is integrated within the link but is still easy to assemble and disassemble. FIG. 13 shows the wrist link configuration and FIGs. 14A-D shows the compact arrangement of joints 6 and 7.

[0099] With space optimized component placement, the joint modules have been made compact thus making the wrist compact.

[0100] Decoupled positioning and orientation:

[0101] Another important feature of the wrist is that the three wrist joints i.e. joint 5, 6 and 7 intersect at a single point as shown in FIG. 15. Having an intersecting wrist allows the positioning and orientation tasks to be decoupled. The wrist point can be positioned by joints 1-4 and the orientation of the operational point can be achieved by joints 5-7. Thus, an object can be oriented in any configuration by using the wrist joints only and be independent of the first four joints.

[0102] Intersecting wrist axes also allows the three wrist joints to be decoupled and reduces the inertia on the joints.

[0103] Singularity free wrist design:

[0104] For a serial kinematic chain wrist design, it can have either roll -pitch-roll or roll-pitch-yaw joint configuration. Majority of the robotic arms are designed with roll-pitch-roll configuration due to mechatronic constraints. The problem with roll-pitch-roll configuration is that the two roll axes align in the middle of the wrist workspace which puts the wrist in singularity. This is problematic because the robot is restricted to operate away from the middle of the workspace which limits the reorientation abilities of the robot or requires more sophisticated controllers. By using a 90-degree flange at the output of joint 7 as shown in FIG. 16, we have an effective rollpitch-yaw configuration and have been able to move the wrist singularity at the boundary of the wrist workspace so the robot can seamlessly operate in the middle of the wrist without getting into singularity and operate with an increased workspace.

[0105] FIG. 17 shows the singularity free wrist design around the middle of the workspace. Singularity occurs at the boundary of the workspace which is no longer a concern.

[0106] 2. Workspace safety guarantee:

[0107] Safety is a big concern with existing robotic arms. To design a safe arm, it is important that the robot does not violate a certain pre-defined workspace which can be programmed for each application. For example, if the robot is taking ultrasound imaging of a patient, the workspace can be configured such that it does not penetrate the patient beyond a certain threshold. This can be done in software, but software is prone to failure and does not provide safety guarantees. Therefore, our arm has configurable hard stops on joints 1-4 which control the position of the wrist point. So, by configuring the joint limits on these modules we can configure the wrist workspace prior to a task. This provides a mechanical guarantee of the workspace and makes the arm intrinsically safe.

[0108] FIG. 18 shows the joint limiter module which has been seamlessly integrated at the output of joints 1-4.

[0109] 3. Coplanar joint frames:

[0110] The arm has been designed such that the frames of all the joints are coplanar as shown in FIG. 19. This allows the arm to have a simplified kinematic model with no link offsets.

[0111] 4. Optimized operational space dynamics:

[0112] The robot joint positions, link lengths and component placement have been optimized to provide maximal operational space linear and angular accelerations. To accomplish this, both the reflected inertia of the robot and the projection of joint torques to produce forces and moments at the operational point have been considered within the desired workspace. This allows the robot to have improved dynamic properties.

[0113] FIG. 9 shows the improvement in effective operational space inertia where Maestro is according to the present invention and the Panda a reference robot.

[0114] 5. Joint module design:

[0115] To have a compact and light weight torque-controlled arm, we have designed compact actuation modules with torque output comparable to commercially available arm joints. FIG. 20 shows the joint module arrangement in the robotic arm.

[0116] Each joint module has brushless DC motor, wave strain gear, torque sensor, motor side (input) and output side encoder, and support bearings.

[0117] • Integrated torque sensor: This allows each joint to be controlled in torque control mode which enables the robot to seamlessly operate in contact space and provides safety in terms of maximum forces and moments the robot can apply which limits impact damage in case of collision with the robot. • Both input and output encoders are used to account for transmission flexibilities and have optional position control capabilities. Input encoders also enable high resolution BLDC commutation.

[0118] • The input and output encoders have been located to the same side. This allows for more space compactness and a single encoder reader board can be used for both the encoder targets.

[0119] • The cross-roller bearing has been located to the link instead of the joint. Thus, providing space compactness and reducing the structural stress on the joint module itself.

[0120] 6. Human friendly design:

[0121] The shape of the robot has been designed with primitive and rounded shapes to make the design human friendly. FIG. 1 shows the comparison between the arm design of the present invention versus the Kuka iiwa robotic arm design.

[0122] 7. Integrated Hand / Sensor attachment:

[0123] To provide support for an array of sensors and end-effectors, an integrated communication bus and power port have been provided.

Claims

CLAIMSWhat is claimed is:

1. A robotic arm, comprising a wrist, wherein the wrist is characterized by having:(a) a first joint module with a first revolute joint having a first axis for roll, a first input link, a first output link, a first torque sensor, a first motor side encoder, a first output link side encoder, and a first motor;(b) a second joint module with a second revolute joint having a second axis for pitch, a second input link, a second output link, a second torque sensor, a second motor side encoder, a second output link side encoder and a second motor; and(c) a third joint module with a third revolute joint having a third axis for yaw, a third input link, a third output link, a third torque sensor, a third motor side encoder, a third output link side encoder and a third motor, wherein the first axis, the second axis and the third axis nominally intersect at substantially a single point with a design tolerance and are arranged in a rollpitch-yaw singularity free joint arrangement, wherein output of the second torque sensor is attached and grounded to the second input link, wherein the second motor is attached to and rotating with the second output link, wherein output of the third torque sensor is attached and rotating with the third output link, and wherein the third motor is attached to and grounded to the second output link.

2. The claim as set forth in claim 1, wherein the design tolerance is up to 25 mm.

3. The claim as set forth in claim 1, wherein the robotic arm further comprises an arm proximal to the wrist, wherein the arm has four joint modules each having revolute joints, wherein all joint frames of the arm are colinear with no offsets from each other.

4. The claim as set forth in claim 1, wherein the first axis and the second axis are mutually orthogonal and intersecting.

5. The claim as set forth in claim 1, wherein the second axis and the third axis are mutually orthogonal and intersecting.

6. The claim as set forth in claim 1, wherein the third axis and a fourth axis of one of the four joint modules of the arm are mutually orthogonal and intersecting.

7. The claim as set forth in claim 1, wherein the first joint module, the second joint module, the third joint module and the four joint modules of the arm each have joint limiter module capable of configuring a bidirectional range of motion of the respective joint module and therewith reconfigure the reachable workspace of the robotic arm.

Images