Design and Implementation of a Bespoke Robotic Manipulator for Extra-corporeal Ultrasound
Summary
This paper introduces the design and implementation of a bespoke robotic manipulator for extra-corporeal ultrasound examination. The system has five degrees of freedom with lightweight joints made by 3D printing and a mechanical clutch for safety management.
Abstract
With the potential for high precision, dexterity, and repeatability, a self-tracked robotic system can be employed to assist the acquisition of real-time ultrasound. However, limited numbers of robots designed for extra-corporeal ultrasound have been successfully translated into clinical use. In this study, we aim to build a bespoke robotic manipulator for extra-corporeal ultrasound examination, which is lightweight and has a small footprint. The robot is formed by five specially shaped links and custom-made joint mechanisms for probe manipulation, to cover the necessary range of motion with redundant degrees of freedom to ensure the patient's safety. The mechanical safety is emphasized with a clutch mechanism, to limit the force applied to patients. As a result of the design, the total weight of the manipulator is less than 2 kg and the length of the manipulator is about 25 cm. The design has been implemented, and simulation, phantom, and volunteer studies have been performed, to validate the range of motion, the ability to make fine adjustments, mechanical reliability, and the safe operation of the clutch. This paper details the design and implementation of the bespoke robotic ultrasound manipulator, with the design and assembly methods illustrated. Testing results to demonstrate the design features and clinical experience of using the system are presented. It is concluded that the current proposed robotic manipulator meets the requirements as a bespoke system for extra-corporeal ultrasound examination and has great potential to be translated into clinical use.
Introduction
An extra-corporeal robotic ultrasound (US) system refers to the configuration in which a robotic system is utilized to hold and manipulate a US probe for external examinations, including its use in cardiac, vascular, obstetric, and general abdominal imaging1. The use of such a robotic system is motivated by the challenges of manually holding and manipulating a US probe, for instance, the challenge of finding standard US views required by clinical imaging protocols and the risk of repetitive strain injury2,3,4, and also by the needs of US screening programs, for instance, the requirement for experienced sonographers to be on-site5,6. With emphases on different functionalities and target anatomies, several robotic US systems, as reviewed in earlier works1,7,8, have been introduced since the 1990s, to improve different aspects of US examination (e.g., long-distance teleoperation9,10,11,12, as well as robot-operator interaction and automatic control)13,14. In addition to the robotic US systems used for diagnostic purposes, robotic high-intensity focused ultrasound (HIFU) systems for treatment purposes have been widely investigated as summarized by Priester et al.1, with some recent works15,16 reporting the latest progress.
Although several robotic US systems have been developed with relatively reliable technologies for control and clinical operation, only a few of them have been successfully translated into clinical use, such as a commercially available tele-ultrasound system17. One possible reason is the low level of acceptance for large-size industrial-looking robots working in a clinical environment, from the point of view of both patients and sonographers. Additionally, for safety management, the majority of the existing US robots rely on force sensors to monitor and control the applied pressure to the US probe, while more fundamental mechanical safety mechanisms to limit the force passively are usually not available. This may also cause concerns when translating into clinical use as the safety of robot operation would be purely dependent on electrical systems and software logic.
With the recent advancements of 3D printing techniques, specially shaped plastic links with custom-made joint mechanisms could provide a new opportunity for developing bespoke medical robots. Carefully designed lightweight components with a compact appearance could improve clinical acceptance. Specifically for US examination, a bespoke medical robot aimed at being translated into clinical use should be compact, with enough degrees of freedom (DOFs) and range of motion to cover the region of interest of a scan; for example, the abdominal surface, including both the top and sides of the belly. Additionally, the robot should also incorporate the ability to perform fine adjustments of the US probe in a local area, when trying to optimize a US view. This usually includes tilting movements of the probe within a certain range, as suggested by Essomba et al.18 and Bassit19. To further address the safety concerns, it is expected that the system should have passive mechanical safety features which are independent of electrical systems and software logic.
In this paper, we present the detailed design and assembly method of a 5-DOF dexterous robotic manipulator, which is used as the key component of an extra-corporeal robotic US system. The manipulator consists of several lightweight 3D-printable links, custom-made joint mechanisms, and a built-in safety clutch. The specific arrangement of the DOFs provides full flexibility for probe adjustments, allowing easy and safe operations in a small area without colliding with the patient. The proposed multi-DOF manipulator aims to work as the main component that is in contact with patients and it can be simply attached to any conventional 3-DOF global positioning mechanism to form a complete US robot with fully active DOFs to perform a US scan.
Protocol
Representative Results
Discussion
Unlike many other industrial robots that have been translated into medical applications, the proposed robotic manipulator described in the protocol was specifically designed for US examinations according to clinical requirements for the range of motion, application of force, and safety management. The lightweight robotic manipulator itself has a wide range of movements sufficient for most extra-corporeal US scanning, without the need for large movements of the global positioning mechanism. As the closest mechanical struc…
Disclosures
The authors have nothing to disclose.
Acknowledgements
This work was supported by the Wellcome Trust IEH Award [102431] and by the Wellcome/EPSRC Centre for Medical Engineering [WT203148/Z/16/Z]. The authors acknowledge financial support from the Department of Health via the National Institute for Health Research (NIHR) comprehensive Biomedical Research Centre award to Guy's & St Thomas' NHS Foundation Trust in partnership with King's College London and King's College Hospital NHS Foundation Trust.
Materials
| 3D-printed link L0 | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 3D-printed link L1 | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 3D-printed link L2 | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 3D-printed link L3 | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 3D-printed link L4 | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 3D-printed end-effector | 3D printing service | 1 | As shown in Figure 1, with the STL file provided |
| 20-teeth spur gear | 3D printing service | 12 | 0.5 module, 5 mm face width, with mounting keyway, as shown in Figure 2, with the STL file provided |
| 18-teeth bevel gear | 3D printing service | 2 | 0.5 module, 5 mm face width, with mounting keyway, as shown in Figure 2, with the STL file provided |
| 120-teeth spur gear (Type A) | 3D printing service | 1 | 0.5 module, 6 mm face width, with mounting keyway, bearing housing, and bore, as shown in Figure 2, with the STL file provided |
| 120-teeth spur gear (Type B) | 3D printing service | 2 | 0.5 module, 6 mm face width, with detent holes, bearing housing, and bore, as shown in Figure 2, with the STL file provided |
| 120-teeth spur gear (Type C) | 3D printing service | 1 | 0.5 module, 6 mm face width, with mounting key, bearing housing, and bore, as shown in Figure 2, with the STL file provided |
| 20-teeth long spur gear | 3D printing service | 1 | 0.5 module, 21.5 mm face width, with mounting keyways, as shown in Figure 2, with the STL file provided |
| 144-teeth bevel gear | 3D printing service | 1 | 0.5 module, 7 mm face width, with mounting keyways, as shown in Figure 2, with the STL file provided |
| Bearing (37 mm O.D and 30 mm I.D) | Bearing Station Ltd., UK | 5 | Bearing size and supplier can be varied |
| Bearing (12 mm O.D and 6 mm I.D) | Bearing Station Ltd., UK | 2 | Bearing size and supplier can be varied |
| Bearing (32 mm O.D and 25 mm I.D) | Bearing Station Ltd., UK | 1 | Bearing size and supplier can be varied |
| Bearing (8 mm O.D and 5 mm I.D) | Bearing Station Ltd., UK | 2 | Bearing size and supplier can be varied |
| Plastic/metal shaft (6 mm O.D, 70 mm long) | TR Fastenings Ltd., UK | 1 | e.g. Could be an M6 bolt and a nut |
| Plastic/metal shaft (5 mm O.D, 70 mm long) | TR Fastenings Ltd., UK | 1 | e.g. Could be an M5 bolt and a nut |
| Ball-spring pairs | WDS Ltd., UK | 4 | Numbers of ball-spring pairs could varied to adjust the triggering force of the clutch |
| Clutch covers | 3D printing service | 2 | 104 mm O.D, 5mm face width, 6 mm bore, as shown in Figure 2, with the STL file provided |
| 3D-printed shaft collar | 3D printing service | 1 | 35 mm O.D and 30 mm I.D, 8mm face width, as shown in Figure 2, with the STL file provided |
| 3D-printed end-effector collar | 3D printing service | 1 | As shown in Figure 2, with the STL file provided |
| Small geared stepper motors | AOLONG TECHNOLOGY Ltd., China | 14 | Part number: GM15BYS; Internal gear ratio 232:1 or 150:1, all acceptable |
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