SPDM Research Articles

Analytical and semi-analytical inverse kinematics of SSRMS-type manipulators with single joint locked failure

Redundant space manipulators, including Space Station Remote Manipulator System (SSRMS), Special Purpose Dexterous Manipulator (SPDM) and European Robotic Arm (ERA), have been playing important roles in the construction and maintenance of International Space Station (ISS). They all have 7 revolute joints arranged in similar configurations, and are referred to as SSRMS-type manipulators.When a joint is locked in an arbitrary position due to some failures, a 7R manipulator degrades to a 6R manipulator. Without a spherical wrist or three consecutive parallel joints, the inverse kinematics of the 6R manipulator is very complex. In this paper, we propose effective methods to resolve the inverse kinematics for different cases of any joint locked in an arbitrary position. Firstly, configuration characteristics of the SSRMS-type redundant manipulators are analyzed. Then, an existing of closed-form inverse kinematics is discussed for locking different joints. Secondly, D–H frames and corresponding D–H parameters of the new 6-DOF manipulator formed by locking a joint in an arbitrary position are re-constructed. A unified table is then created to describe the kinematics for all possible cases of single joint locking failure. Thirdly, completely analytical and semi-analytical methods are presented to solve the inverse kinematics equations, and the former is used for locking joint 1, 2, 6 or 7 while the latter for locking joint 3, 4 or 5. Finally, typical cases for single joint locking are studied. The results verify the proposed methods.

Eos is out of this world—literally

When the space shuttle Endeavour launched on its 25th and final flight, AGU member and astronaut Andrew J. Feustel took with him a special bit of cargo: an issue of Eos. The accompanying photograph with the image of Eos, taken on 23 May 2011, shows the 15 February issue of Eos floating in front of one of the International Space Station windows. Below and left of the issue is the wing of Endeavour; also visible is the radiator panel on the shuttle's payload bay door. The thin blue line to the right of the issue is Earth's atmosphere. The STS‐134 mission, the second to last space shuttle mission, launched on 16 May and returned to Earth on 1 June. It delivered the Alpha Magnetic Spectrometer (a particle physics experiment module) to the International Space Station along with two communications antennas, a high‐pressure gas tank, and parts for the two‐armed Special Purpose Dexterous Manipulator (Dextre) robot. The final shuttle mission, STS‐135, launched on 8 July.

Identification of Contact Parameters from Stiff Multi-point Contact Robotic Operations

Computer simulations play an important role in the design and validation of constrained robotic operations. The fidelity of these simulations, however, depends on the specification of contact dynamics parameters, which often need to be determined experimentally. In this paper we investigate the identification of contact parameters from complex stiff multi-point contact scenarios encountered in typical robotic operations using a recently developed least-squares-based method. This method is extended to deal with geometric uncertainties by employing a non-linear separable least-squares formulation. The latter is solved using a variable projection method, and allows simultaneous identification of contact parameters and geometric uncertainties. The conditions for observability of geometric uncertainties are derived and a regularized formulation is proposed in case the identification of geometric uncertainties is ill-conditioned. The applicability of the original method and the benefits of the extended method with identification of geometric uncertainties for the identification of the contact parameters are illustrated by means of experimental data measured with the Special Purpose Dexterous Manipulator (SPDM) Task Verification Facility (STVF) manipulator at the Canadian Space Agency (CSA).

Identification of Contact Dynamics Parameters for Stiff Robotic Payloads

This paper investigates and demonstrates the feasibility of identifying contact dynamics parameters for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">stiff</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">robotic</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">payloads</i> using a robotic system. The contact dynamics model for stiff payloads is motivated, and theoretical parameter values and bounds are provided. Then, the effect of nonidealities such as surface roughness and plastic deformation on the theoretical values is demonstrated. A row-wise-scaled total least-squares parameter estimation algorithm is proposed and applied to experimental data measured using the special purpose dexterous manipulator task verification facility manipulator at the Canadian Space Agency. The experimental results are compared to a separate set of experiments with a material testing machine as well as finite-element modeling results. Finally, the experimental findings are generalized by providing guidelines for the maximum identifiable payload stiffness as a function of the position resolution, the maximum exertable force, and the structural stiffness of the robotic system.

Dextre: Improving maintenance operations on the International Space Station

The Special Purpose Dexterous Manipulator (SPDM), known as “Dextre”, is currently slated to launch in February 2008 for deployment on the International Space Station (ISS) as the final component of Canada's Mobile Servicing System (MSS). Dextre's primary role on the Space Station is to perform repair and replacement (R&R) maintenance tasks on robotically compatible hardware such as Orbital Replaceable Units (ORUs), thereby eventually easing the burden on the ISS crew. This burden on the on-orbit crew translates practically into crew time being a limited resource on the ISS, and as such, finding ways to assist the crew in performing their tasks or offloading the crew completely when appropriate is a bonus to the ISS program. This is already accomplished very effectively by commanding as many non-critical robotics tasks as possible, such as powering up and free-space maneuvering of the Space Station Remote Manipulator System (SSRMS), known as “Canadarm2”, from the Ground. Thus, beyond its primary role, and based on an increasing clarity regarding the challenges of external maintenance on the ISS, Dextre is being considered for use in a number of ways with the objective of improving ISS operations while reducing and optimizing the use of crew time through the use of ground control for various tasks, pre-positioning hardware, acting as a temporary storage platform to break an Extra Vehicular Activity (EVA) day into manageable timelines, and extending the physical reach and range of the Canadarm2. This paper discusses the planned activities and operations for Dextre an rationale for how these will help optimize the use of crew resources on the ISS.

Improving Robotic Operator Performance Using Augmented Reality

Robotic operations performed in earth orbit face unique challenges. In the case of the Special Purpose Dexterous Manipulator (SPDM), a two-armed robotic device, operations can last multiple orbital days, with dynamic sunlit days and very dark nights. Direct and indirect visibility can be difficult. This project developed and tested the use of augmented reality technology with a ground based trainer to reduce the negative effects of these conditions. Results of the project showed that twelve skilled operators can significantly reduce positioning errors and time to task completion when using augmented reality techniques.

Command and Telemetry Latency Effects on Operator Performance during International Space Station Robotic Operations

International Space Station operations require onboard crewmembers to perform numerous robotic assembly, maintenance, and inspection activities. Ground-based control of the Mobile Servicing System (MSS), in particular the Special Purpose Dexterous Manipulator (SPDM), has been identified as one potential solution to alleviate disproportionate robotic maintenance and inspection timelines that potentially exceed crew availability and duty times. Challenges to operator performance and safety of ground-based control of these manipulators include significant data and telemetry latency. Recent trends of transmissions between the International Space Station and NASA's Mission Control Center have determined the round-trip time delay can range from 6-8 seconds. The purpose of this study was to examine operator performance when subjects performed representative dexterous robotic tasks with anticipated command and telemetry time delays. Results from this study may determine whether augmentations to existing operator tools and procedures are required in order to manually control the SPDM from ground-based workstations.

On the Validation of SPDM Task Verification Facility

This paper describes a methodology for validating a ground-based, hardware-in-the-loop, space-robot simulation facility. This facility, called SPDM task verification facility, is being developed by...

On the Validation of SPDM Task Verification Facility

AbstractThis paper describes a methodology for validating a ground‐based, hardware‐in‐the‐loop, space‐robot simulation facility. This facility, called “SPDM task verification facility,” is being developed by the Canadian Space Agency for the purpose of verifying the contact dynamics performance of the special purpose dexterous manipulator (SPDM) performing various maintenance tasks on the International Space Station because the real SPDM cannot be physically tested for 3D operations on the ground due to the gravity. The facility uses a high‐fidelity SPDM mathematical model, known as the “truth model” of the space robot, to drive a hydraulic robot to mimic the space robot performing contact operations. In this research different techniques were studied for practically verifying that the complex simulation facility preserves the dynamics of the truth model of the space robot for space‐representative contact robotic tasks. Based upon the study and many years of experience in developing and verifying space robotic systems, a practical validation strategy including detailed test cases was developed along with a set of quantitative criteria for judging the validation test results. © 2004 Wiley Periodicals, Inc.

Sensory Limitations of the International Space Station's Robotic Maintenance Systems

The tele-operated Special Purpose Dexterous Manipulator (SPDM) will be used on the International Space Station to exchange failed orbital replaceable units (ORUs) for functional ones. Use of the SPDM will help reduce the burden on astronauts to perform these external maintenance tasks. Limited sensing capability on the SPDM, however, in combination with complex ORU worksites make the exchange of ORUs challenging tele-robotically. Position and force information constitute the primary sensor feedback to the operator. The operator also has limited camera views with which to monitor and direct the task. This paper describes the tele-sensing capabilities of the robotic maintenance system and proposes design concepts to supplement these capabilities.

Velocity degeneracy determination for the kinematically redundant CSA/ISE STEAR testbed manipulator

The Canadian Space Agency (CSA)/International Submarine Engineering (ISE) STEAR Testbed Manipulator (STM) is a ground-based manipulator similar to the arms of the Special Purpose Dextrous Manipulator (SPDM) being built for the International Space Station (ISS). This work presents the determination of the velocity-degenerate (singular) configurations for the STM, a system comprised of two seven-jointed redundant manipulators. The two “arms” of the STM are mirror images of one another. The analysis presented is for the STM-1 or “right” arm, but it applies to the STM-2 or “left” arm since they are mirror images and have similar dimensions and joint ranges. A methodology based on reciprocity of screws is used to identify all configurations causing one degree-of-freedom (DOF) instantaneous motion loss in the STM. It is shown that there are five families of two-condition configurations resulting in a single DOF loss for manipulators kinematically similar to the STM-1. Reciprocal screws characterizing the lost motion DOF for each of the degenerate configurations are derived. Analysis of the velocity degeneracies shows that for the STM-1 dimensions and joint limits, only four of the five velocity-degenerate configurations are feasible. © 2000 John Wiley & Sons, Inc.

Control strategies for hardware-in-the-loop simulation of flexible space robots

As a partner in the International Space Station (ISS), Canada is responsible for the verification of all tasks involving the special purpose dextrous manipulator (SPDM). Those verifications cannot be performed using software simulators only since the accuracy of existing contact dynamic models are yet to be confirmed, especially in the real-time mode required for verifying human operated processes. One option is to use a hardware-in-the-loop simulation (HLS), where the space hardware is simulated and the contact dynamics is emulated using a rigid robot performing the tasks. The main difficulty in this approach is the trade-off between the stability of the control loop and good performance. The control of the rigid robot in the HLS is investigated. Simplified linear systems are used to determine the limitations of the classical position-based control when contact occurs. A new control scheme in which the slave robot is driven in acceleration is proposed. Both methods were tested experimentally and the results show the benefit of using this new acceleration control approach.

The Special Purpose Dexterous Manipulator (SPDM) Systems Engineering Effort – A successful exercise in cheaper, faster and (hopefully) better systems engineering

The Special Purpose Dexterous Manipulator (SPDM) is the latest Space Robot developed by the Canadian Space Agency (CSA) and McDonald Detwiller Space and Advanced Robotics (MD Robotics, previously Spar Aerospace) for the International Space Station (ISS). The SPDM has presented its designers with a number of new challenges in performing the Systems Engineering effort required for a complex robotic system: (1) The SPDM initial design was started and attained various levels of maturity for various components under the Space Station Freedom environment, then the Program was stopped and finally restarted under the harsher environment in which the International Space Station is being built. (2) The SPDM is the first space robot to utilize previously developed and space certified robotic components, as well as components with high-commonality to the previously developed ones (electronics, S/W). (3) New requirements levied by the Customer during the negotiations leading to the Program re-start necessitated significant architectural changes versus the SPDM configuration `frozen' when the Program was shut down. (4) The SPDM is the first robotic system of this complexity that is being built under a Firm Fixed Price contract, with the commonality assumptions as one of the cost drivers. This combination of components of various pedigree, coupled with the constraints imposed by an FFP contract have been addressed by the designers through the definition of a novel approach to integrated Systems and Design Engineering.

Canadian space robotic activities

The Canadian Space Agency has chosen space robotics as one of its key niche areas, and is currently preparing to deliver the first flight elements for the main robotic system of the international space station. The Mobile Servicing System (MSS) is the Canadian contribution to the international space station. It consists of three main elements. The Space Station Remote Manipulator System (SSRMS) is a 7-metre, 7-dof, robotic arm. The Special Purpose Dextrous Manipulator (SPDM), a smaller 2-metre, 7-dof, robotic arm can be used independently, or attached to the end of the SSRMS. The Mobile Base System (MBS) will be used as a support platform and will also provide power and data links for both the SSRMS and the SPDM. A Space Vision System (SVS) has been tested on Shuttle flights, and is being further developed to enhance the autonomous capabilities of the MSS. The CSA also has a Strategic Technologies in Automation and Robotics Program which is developing new technologies to fulfill future robotic space mission needs. This program is currently developing in industry technological capabilities in the areas of automation of operations, autonomous robotics, vision systems, trajectory planning and object avoidance, tactile and proximity sensors, and ground control of space robots. Within the CSA, a robotic testbed and several research programs are also advancing technologies such as haptic devices, control via head-mounted displays, predictive and preview displays, and the dynamic characterization of robotic arms. Canada is also now developing its next Long Term Space Plan. In this context, a planetary exploration program is being considered, which would utilize Canadian space robotic technologies in this new arena.

Space robotics and manipulators — The past and the future

Abstract This paper presents the current state of the technology in space robotics. Some historical developments and the experience gained during those projects have been discussed. The challenge of space exploration and related danger requires even larger use of robotic devices. Many tasks and jobs are being automated. The exploration of the Moon and Mars requires autonomous, mobile robots to gather various information, measurements and data. The introduction of the Space Shuttle and related activities required an efficient robotic manipulator for in orbit operations. The Space Station Mir (in-orbit) and especially Space Station Freedom or Alpha (planned for the very near future) require advanced robots and manipulators. The Space Station Remote Manipulator System (SSRMS) and Special Purpose Dextrous Manipulator (SPDM) have been shown and briefly reviewed. Those and other robots for future missions are discussed in this paper.

Advanced Control System Features of the Space Station Remote Manipulator System

The Space Station Remote Manipulator System (SSRMS) is part of Canada's contribution to Space Station “Freedom“. This large manipulator will be used during the assembly and operation of the station to perform tasks such as the assembly of truss segments and pressurized modules, berthing the Shuttle Orbiter, and positioning EVA astronauts as well as the Special Purpose Dexterous Manipulator. This paper provides an overview of the role and configuration of the SSRMS and discusses the major SSRMS payload handling requirements. The SSRMS control systems and its operating modes are described, with focus on the Force/Moment Accommodation and the Artificial Vision systems. The utility of these advanced features is illustrated by simulation and test results

Space Robotics and Manipulators: Lessons Learned From the Past and Future Missions and Systems

Abstract This paper presents the current state of the technology in space robotics. Some historical developments and the experience gained during those projects have been discussed. The challenge of space exploration and related danger requires even larger use of robotics devices. Many tasks and jobs are being automated. The exploration of the Moon and Mars requires the autonomous, mobile robots to gather various information, measurements and data. An introduction of Space Shuttle and related activities required an efficient robotic manipulator for in orbit operations. The Space Station Mir (in orbit) and especially Space Station Freedom (planned for nearest future) require advanced robots and manipulators. The Space Station Remote Manipulator System (SSRMS) and Special Purpose Dextrous Manipulator (SPDM) have been shown and briefly reviewed. Those and other robots for future missions are discussed in this paper.