Magnetic Brake

Space Segment - Platform

Status

Completed
Status date

2023-07-10
Activity Code

4E.072.

Objectives

EM_MagBrak_1

The objective of the activity is to design, develop, manufacture and test a high-resolution magnetic brake solution to increase the unpowered holding torque of rotary actuators used in mechanisms for telecoms applications (e.g. appendage deployment and positioning).

The main specifications given by ESA are:

Minimum 200 stable braking positions
Targeted holding torque: 120mNm
No tribological layers. No generation of debris
Inner diameter: 35mm
Length: 15mm
Outer diameter: 55mm
Mass lower 150g
Operating qualification temperature: -45°C - +100°C
Mechanical override without damage
Fully redundant power lines
Minimum power consumption
In-orbit life duration of minimum 15 years
ITAR free

Challenges

The main challenges are:

Common „magnetic brakes“ use tribological layers as brake. Only actuation is done electromagnetically.
Eddy current brakes do only provide holding torque while movement (e.g. rotation of axis).
Hysteresis brakes provide even holding torque without movement but tend to have stepping even in released mode (ripple)
Active) reluctance brakes are not commonly available and rare information on products / prototypes is found.

A completely new technology has to be invented.

Benefits

The magnetic brake provides up to 176mNm holding torque at a size to fit the SAGEM21PP in environment from air to vacuum and from -45°C up to +100°C. The brake’s state is toggled between release / brake with an electric impulse of 21V, 7.8A and 10ms - no special electronics is needed. The design is easily adaptable to customer needs to fit other actuators with a different size or different number of stable positions. The magnetic brake has no tribological layer - no generation of debris. In case of faulty operation, the motor can actively override it without damage. The costs for a magnetic brake as commonly available serial product (ITAR free) are estimated to be clearly below 10k€.

The magnetic brake enables the usage of smaller actuators and / or safe energy by switching off the actuator and use the magnetic brake to provide the necessary holding torque (instead of the powered actuator). No comparable competitor products are available.

Features

The magnetic brake is fully compliant to the specifications given by ESA and potential customers:

Size (fits to SAGEM21PP):
- Inner diameter: 13mm
- Outer diameter: 51mm
- Length: 10mm
Holding torque: 0.176Nm
200 stable positions
No permanent power for locked or released state necessary
Minimum switching power: 164 W; min. switching energy: 1,65 Ws (21V /7.8A / 10ms)
Voltage level: 20-32V (lower voltage leads to lower holding torque / no fully release)
Fully redundant design
Total mass: 150g
No tribological layer – no generation of debris
Mechanical override without damage possible
Tested on shaker without damage
Operational temperature range: -45°C to +100°C
ITAR free
Compliant to ECSS-Q-ST-70-02
Endless rotation / no speed limitation
No complex electronics necessary
Can be easily adapted to fit other actuators

System Architecture

The magnetic brake consists of stator and rotor, which need to be integrated onto the customers actuator stator and rotor. The axis of the customers actuator has to take up the rotor of the magnetic brake. Additional adjustment tools to align the magnetic brake to the customers actuator are available – especially for synchronization of magnetic brake with a stepper motor.

All parts of the magnetic brake Engineering Model are already produced in close-to-production techniques to proof high quality and still meet the harsh cost criteria of potential end-users. Actuation is done without complex electronics, only an electric pulse is needed to toggle the brake’s state.

Plan

The project is processed in 7 steps:

Review of State-of-the-Art and Application Survey
Finalised Technical Requirements and Selection of Baseline Solution – Milestone: Specification Review
Magnetic brake Breadboard version: design and hardware – Miilestone: Preliminary Design Review
Breadboard performance characterisation
Magnetic brake Engineering Model design and adaptation of baseline actuator – Milestone: Design Review
Engineering Model and full assembly (with actuator) performance characterisation
Overall Evaluation – Milestone: Final Report

Current status

The project has been completed. Magnetic Brake Breadboard Model and Engineering Model are designed, built and tested. The Engineering Model is fully compliant to the specifications of ESA and the input of potential customers are considered as well – especially the cost requirements for a serial product could be met as well.