Pneumatic Stepper Motors Research Articles

Motion Accuracy of Pneumatic Stepper Motor-Driven Robotic System Developed for MRI-Guided High-Intensity Focused Ultrasound Treatment of Prostate Disease

The latest advancement in high-intensity focused ultrasound (HIFU) treatment technology integrates magnetic resonance imaging (MRI) guidance for precise treatment of prostate disease. As conventional electromagnetic motors are not applicable for utilization within MRI scanners, we have developed a prototype robotic system driven by pneumatic stepper motors to control the movement of the HIFU transducer within an intrarectal probe during MRI-guided HIFU treatment procedures. These pneumatic stepper motors were constructed entirely from MRI-compatible plastic materials. Assessment of the robotic system’s MRI compatibility was conducted utilizing a 3.0T MRI scanner, revealing no discernible MRI image distortion with a minor decrease in the signal-to-noise ratio (2.8%) during the motor operation. The robotic system enabled the transducer to move inside the probe with two degrees of freedom, allowing both linear and rotational motion. The positional accuracy of the transducer movement was assessed, yielding ±0.20 and ±0.22 mm accuracies in the forward and backward linear movements, respectively, and ±0.79° and ±0.74° accuracies in the clockwise and counterclockwise rotational motions, respectively. Emulation of authentic HIFU procedures involved creating a two-dimensional array of thermal lesions in a tissue-mimicking phantom, achieving positional accuracy within ±1 mm for the generated HIFU focal spots. The prototype robotic system incorporating pneumatic stepper motors fabricated entirely from MRI-compatible plastic materials has demonstrated the requisite positional accuracy necessary for effective HIFU treatment of prostate disease, indicating substantial promise for future clinical application.

An Opposed Piston Driving Pneumatic Stepper Motor for MR Intervention Robotics

Magnetic resonance (MR) safe robots offer many advantages to robot-assisted surgeries in the magnetic resonance imaging (MRI) environment. As one of the key components, the design of actuators that work in the MR environment is critical for MR safe robots. This article proposed a new piston motor powered by compressed air for MR safe robots, in which the working principle is investigated, and the dynamic model is analyzed. Linear motion is achieved by applying the lead screw transmission. Experiments demonstrate that the rotary motor has a maximum speed of 800 r/min and maximum output torque of 132 mN·m, and the linear motor has an output force of 50 N, both at a speed of 2 steps/s. The step response and error analysis are also conducted. MR tests show that there are no obvious image artifacts caused by the motor.

PneuAct-II: Hybrid Manufactured Electromagnetically Stealth Pneumatic Stepper Actuator

Additive manufacturing (AM) is one of the emerging production methodologies transforming the industrial landscape. However, application of the technology in fluidic power transmission and actuation is still limited. AM pneumatic stepper motors have been previously introduced to the field of image-guided surgical robotics, where their disposability and customizability are considered a significant advantage over conventional manufacturing. However, intrinsic dimensional limitations of AM parts and their poor surface quality affect mechanical performance. In this letter, a novel design, PneuAct-II, is presented combining AM, subtractive machining, and off-the-shelf components to achieve higher mechanical performance and resolution. Moreover, a motor identification setup has been built to automatically measure different aspects of the PneuAct motors, including wear, friction, leakage, and stall behavior at various boundary conditions. The effects of input pressure, stepping frequency, signal-width, and external torque on the stall behavior of motors with different clearances are studied. A maximum torque of 0.39 N $\cdot$ m at an input pressure of 6.5 bar is achieved for a motor with a total volume of 90 cm $^3$ , and a clearance of 156 $\mu$ m. A nominal resolution of 2.25 $^{\circ }$ at full-pitch and 1.125 $^{\circ }$ at half-pitch is accomplished. Both resolution and mechanical performance (667 N $\cdot$ m/bar $\cdot$ m $^3$ ) outperform the state-of-the-art (240 N $\cdot$ m/bar $\cdot$ m $^3$ by PneuAct-I).

Evaluation of MRI-compatible pneumatic muscle stepper motors

Abstract The automation of instruments and tools (e.g. bone drill) or robotic devices (e.g. needle positioning robot for prostate surgery) for use in interventional MRI (iMRI) is still challenging due to a lack of accurate, affordable and completely metal-free actuators and motors. Inspired by biological muscles, a bionic equivalent known as the fluid muscle actuator (which can be operated pneumatically or hydraulically) is well-known in the mechanical engineering industry. Fluid muscle actuators have multiple beneficial characteristics: they are simple, self-returning, low-friction and can produce relatively high actuation forces at low diameters and pressures. We present two novel designs for metal-free, pneumatic stepper motors for potential application in iMRI. Our stepper motors are powered by simple pneumatic muscles, which are assembled from low-cost off-the-shelf components. Besides, the components of the stepper motor demonstrators were 3Dprinted using a stereolithographic additive manufacturing process (SLA printing). We evaluate the effect of pneumatic muscle length on contractile force and length. Our results demonstrated the functional feasibility of the pneumatic muscle-powered and fully MRI-compatible stepper motor designs. In a next step, we will optimize the motor´s design, characterize their performance and reliability, and use the stepper motors to power a micropositioning device in iMRI-phantom tests.

High Speed Pneumatic Stepper Motor for MRI Applications.

Presented in this paper is an exploration into the efficacy of a plastic, four-cylinder piston pneumatic motor designed for driving medical instruments inside magnetic resonance imaging (MRI) systems. Because of the increasing use of MRI for diagnostic and interventional purposes and the benefits that could be realized by operating with real-time MR image guidance, there exists a significant need for MRI compliant surgical devices. Some type of actuation mechanism is necessary to drive such devices. The motor can be controlled to operate in a "step" type motion by using pneumatic valves to sequentially apply air pressure to push the piston surfaces, meaning the motor is metal-free and does not use electricity. The stepwise nature of this piston stepper motor is ideal for the accurate, controlled movements required for MRI-guided interventions. The motor was geared down by a gearbox to increase torque. Performance indices determined include output torque and achievable rotational velocity with respect to factors such as air pressure and load conditions. The stepper motor achieved speeds of approximately 2000rpm, and maximum output torques of approximately 19Nmm. The motor represents a high speed pneumatic stepper motor design capable of actuating devices in MR environments without affecting image quality.

Rapid Prototyping High-Performance MR Safe Pneumatic Stepper Motors

In this paper, we show that magnetic resonance (MR) safe pneumatic stepper motors can be constructed using rapid prototyping techniques such as 3-D printing and laser-cutting. The designs are lightweight, metal-free, and fully customizable. Besides MR safe robotic systems, other potential applications include high-voltage switchgear and nuclear power plant systems, which also restrict electric actuation. In addition, it can be applied to other actuation systems, where pressurized air is available, and lightweight rapid prototypeable actuators are needed. Five pneumatically driven linear and rotational stepper motors have been developed with forces up to $\text{330 N}$ , torques up to 3.7 N $\cdot$ m, the stepping frequency up to 320 Hz, dimensions ranging from 25 to 80 mm, free of backlash, and power up to 26 W. All five motors are constructed from six 3-D printed parts and four seals, held together by nylon screws or clips. The described stepper motors outperform state-of-the-art plastic pneumatic stepper motor designs, both in specifications and in manufacturability.

Stormram 4: An MR Safe Robotic System for Breast Biopsy

Suspicious lesions in the breast that are only visible on magnetic resonance imaging (MRI) need to be biopsied under MR guidance with high accuracy and efficiency for accurate diagnosis. The aim of this study is to present a novel robotic system, the Stormram 4, and to perform preclinical tests in an MRI environment. Excluding racks and needle, its dimensions are 72 × 51 × 40 mm. The Stormram 4 is driven by two linear and two curved pneumatic stepper motors. The linear motor is capable of exerting 63 N of force at a pressure of 0.65 MPa. In an MRI environment the maximum observed stepping frequency is 30 Hz (unloaded), or 8 Hz when full force is needed. The Stormram 4’s mean positioning error is 0.73 ± 0.47 mm in free air, and 1.29 ± 0.59 mm when targeting breast phantoms in MRI. Excluding the off-the-shelf needle, the robot is inherently MR safe. The robot is able to accurately target lesions under MRI guidance, reducing tissue damage and risk of false negatives. These results are promising for clinical experiments, improving the quality of healthcare in the field of MRI-guided breast biopsies.

Erratum to:An MR-Conditional High-Torque Pneumatic Stepper Motor for MRI-Guided and Robot-Assisted Intervention.

Erratum to:An MR-Conditional High-Torque Pneumatic Stepper Motor for MRI-Guided and Robot-Assisted Intervention.

Laser-Cutting Pneumatics

Pneumatic devices require tight tolerances to keep them leak-free. Specialized companies offer various off-the-shelf devices, while these work well for many applications, there are also situations where custom design and production of pneumatic parts are desired. Cost efficiency, design flexibility, rapid prototyping, and MRI compatibility requirements are reasons why we investigated a method to design and produce different pneumatic devices using a laser cutter from acrylic, acetal, and rubber-like materials. The properties of the developed valves, pneumatic cylinders, and stepper motors were investigated. At 4-bar working pressure, the 4/3-way valves are capable of 5-Hz switching frequency and provide at most 22-L/min airflow. The pneumatic cylinder delivers 48 N of force, the acrylic stepper motor 30 N. The maximum switching frequency over 6-m long transmission lines is 4.5 Hz, using 2-mm tubing. A MRI-compatible robotic biopsy system driven by the pneumatic stepper motors is also demonstrated. We have shown that it is possible to construct pneumatic devices using laser-cutting techniques. This way, plastic MRI-compatible cylinders, stepper motors, and valves can be developed. Provided that a laser-cutting machine is available, the described pneumatic devices can be fabricated within hours at relatively low cost, making it suitable for rapid prototyping applications.

Novel Design and 3-D Printing of Nonassembly Controllable Pneumatic Robots

Additive manufacturing (known as 3-D printing to the public) technologies are capable of fabricating mechanical parts without the limitation of geometric complexity. If properly designed, a mechanism can also be automatically fabricated without the need of assembly. Considering these capabilities of 3-D printing, this paper presents a novel pneumatic robot design that can be fabricated by 3-D printing processes without the need of assembly. The key element of the proposed robot is the innovative design of a pneumatic stepper motor that allows control of multimotion pattern modes. The proposed pneumatic stepper design is based on a fan motor, thus, having a low requirement on airtightness, which makes it possible for 3-D printing fabrication. For angular motion control, a roller valve is added to the fan motor design. By controlling the air pressure of the roller valve, continuous motion and stepping motion can be obtained. Experiments have shown that the angular velocity can also be controlled by varying the roller-valve air pressure. The effectiveness of the proposed concepts has been demonstrated by a 3-D printed nonassembly pneumatic robot. The printed robot, when connected with air tubes and a pneumatic controller, can perform simple pick and place operations. It is argued that the future functional nonassembly pneumatic robotic systems could be 3-D printed for relevant industries.

A low-cost, high-field-strength magnetic resonance imaging-compatible actuator.

To perform minimally invasive surgical interventions with the aid of robotic systems within a magnetic resonance imaging scanner offers significant advantages compared to conventional surgery. However, despite the numerous exciting potential applications of this technology, the introduction of magnetic resonance imaging-compatible robotics has been hampered by safety, reliability and cost concerns: the robots should not be attracted by the strong magnetic field of the scanner and should operate reliably in the field without causing distortion to the scan data. Development of non-conventional sensors and/or actuators is thus required to meet these strict operational and safety requirements. These demands commonly result in expensive actuators, which mean that cost effectiveness remains a major challenge for such robotic systems. This work presents a low-cost, high-field-strength magnetic resonance imaging-compatible actuator: a pneumatic stepper motor which is controllable in open loop or closed loop, along with a rotary encoder, both fully manufactured in plastic, which are shown to perform reliably via a set of in vitro trials while generating negligible artifacts when imaged within a standard clinical scanner.

An MR-conditional high-torque pneumatic stepper motor for MRI-guided and robot-assisted intervention.

Magnetic resonance imaging allows for visualizing detailed pathological and morphological changes of soft tissue. MR-conditional actuations have been widely investigated for development of image-guided and robot-assisted surgical devices under the Magnetic resonance imaging (MRI). This paper presents a simple design of MR-conditional stepper motor which can provide precise and high-torque actuation without adversely affecting the MR image quality. This stepper motor consists of two MR-conditional pneumatic cylinders and the corresponding supporting structures. Alternating the pressurized air can drive the motor to rotate each step in 3.6° with the motor coupled to a planetary gearbox. Experimental studies were conducted to validate its dynamics performance. Maximum 800mNm output torque is achieved. The motor accuracy independently varied by two factors: motor operating speed and step size, was also investigated. The motor was tested within a 3T Siemens MRI scanner (MAGNETOM Skyra, Siemens Medical Solutions, Erlangen, Germany) and a 3T GE MRI scanner (GE SignaHDx, GE Healthcare, Milwaukee, WI, USA). The image artifact and the signal-to-noise ratio (SNR) were evaluated for study of its MRI compliancy. The results show that the presented pneumatic stepper motor generated 2.35% SNR reduction in MR images. No observable artifact was presented besides the motor body itself. The proposed motor test also demonstrates a standard to evaluate the pneumatic motor capability for later incorporation with motorized devices used under MRI.