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 injury^2,3,4, and also by the needs of US screening prog....

Protocol

1. Preparation of Each Link, End-effector, and Additional Components

1. Print all the links (L₀, L₁, L₂, L₃, and L₄) and the end-effector as shown in Figure 1, with acrylonitrile butadiene styrene (ABS) plastic, polylactic acid (PLA) plastic, or nylon, using a 3D-printing service. Use the .STL files provided in the Supplementary Materials when printing.
   NOTE: Changes in shape and scale of each part can be made based on the provided files. The inner profile of the end-effector can be changed to fit different US probes.
2. Print all the required a....

Results

Following the protocol, the resulting system is a robotic manipulator with five specially shaped links (L₀ to L₄) and five revolute joints (J₁ to J₅) for moving, holding, and locally tilting a US probe (Figure 8). The top rotation joint (J₁), with gear mechanisms actuated by four motors, can rotate the following structures 360°, to allow the US probe to point toward different sides of the scanning area, s.......

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.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
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