Robert Anton Brookhuis

Six-axis force-torque sensor with a large range for biomechanical applications

A silicon six-axis force–torque sensor is designed and realized to be used for measurement of the power transfer between the human body and the environment. Capacitive read-out is used to detect all axial force components and all torque components simultaneously. Small electrode gaps in combination with mechanical amplification by the sensor structure result in a high sensitivity. The miniature sensor has a wide force range of up to 50 N in normal direction, 10 N in shear direction and 25 N mm of maximum torque around each axis.

Miniature large range multi-axis force-torque sensor for biomechanical applications

A miniature force sensor for the measurement of forces and moments at a human fingertip is designed and realized. Thin silicon pillars inside the sensor provide in-plane guidance for shear force measurement and provide the spring constant in normal direction. A corrugated silicon ring around the force sensitive area provides the spring constant in shear direction and seals the interior of the sensor. To detect all load components, capacitive read-out is used. A novel electrode pattern results in a large shear force sensitivity. The fingertip force sensor has a wide force range of up to 60 N in normal direction, ± 30 N in shear direction and a torque range of ± 25 N mm.

Three-axial force sensor with capacitive read-out using a differential relaxation oscillator

A silicon three-axis force sensor is designed and realized to be used for measurement of the interaction force between a human finger and the environment. To detect the force components, a capacitive read-out system using a novel relaxation oscillator has been developed with an output frequency proportional to differential capacitance. The sensor has a range of 2N in tangential- and normal force direction with an accuracy better than 1.5% of the full-scale. The sensor can be safely overloaded with a normal force of more than 30N.

Scalable six-axis force-torque sensor with a large range for biomechanical applications

A scalable silicon six-axis force-torque sensor is designed and realized to be used for measurement of the power transfer between the human body and the environment. Capacitive readout is used to detect all axial force components and all torque components simultaneously. Small electrode gaps in combination with mechanical amplification by the sensor structure result in a high sensitivity. The miniature sensor has a wide force range of up to 50 N in normal direction, 10 N in shear direction and 25 N-mm of maximum torque around each axis, and can easily be scaled to adapt for other force/torque ranges.

Three-axis force-torque sensor with fully differential capacitive readout

We present a 3-axis force/torque sensor fabricated in a single SOI wafer. The sensor allows fully differential capacitive readout also for the normal force measurement, without the need for complicated lever mechanisms or wafer bonding. Fabrication is straightforward, with only two masks for deep reactive ion etching and one release etch. Furthermore, out-of-plane displacements are limited by the buried oxide layer thickness which allows for overload protection. The chip has a diameter of 5 mm, a normal force range of 1 N and a torque range from -4 to +4 Nmm and is designed for measuring the interaction forces involved in eye surgery.

Proportional Control Valves Integrated in Silicon Nitride Surface Channel Technology

We have designed and realized two types of proportional microcontrol valves in a silicon nitride surface channel technology process. This enables on-die integration of flow controllers with other surface channel devices, such as pressure sensors or thermal or Coriolis-based (mass) flow sensors, to obtain a proportional gas flow control system on a single chip. One valve design is implemented with inlet and outlet channels in the plane of the chip, which allows on-chip flow control between several fluidic components and allows up to 70 mgh-1 of flow at 200 mbar. The other valve design operates out-of-plane between surface channels and a fluidic inlet, offering a flow range up to 1250 mgh-1 at 600 mbar, smaller footprint, and low-leakage closure. Measured flow behavior agrees well with laminar flow models created for both valve types.

A piezoelectric micro control valve with integrated capacitive sensing for ambulant blood pressure waveform monitoring

We have designed and characterized a MEMS microvalve with built-in capacitive displacement sensing and fitted it with a miniature piezoelectric actuator to achieve active valve control. The integrated displacement sensor enables high bandwidth proportional control of the gas flow through the valve. This is an essential requirement for non-invasive blood pressure waveform monitoring based on following the arterial pressure with a counter pressure. Using the capacitive sensor, we demonstrate negligible hysteresis in the valve control characteristics. Fabrication of the valve requires only two mask steps for deep reactive ion etching (DRIE) and one release etch.

Nano-G accelerometer using geometric anti-springs

We report an ultra-sensitive seismic accelerometer with nano-g sensitivity, using geometric anti-spring technology. High sensitivity is achieved by an on-chip mechanical preloading system comprising four sets of curved leaf springs that support a proof-mass. Using this preloading mechanism, stiffness reduction up to a factor 26 in the sensing direction has been achieved. This increases the sensitivity to acceleration by the same factor. The stiffness reduction is independent of the proof-mass position, preserving the linear properties of the mechanics and due to its purely mechanical realization, no power is consumed when the accelerometer is in its preloaded state. Equivalent acceleration noise levels below 2ng/√Hz have been demonstrated in a 50 Hz bandwidth, using a capacitive half-bridge read-out.

Miniature force-torque sensors for biomechanical applications

The forces involved in interactions between the human body and the environment are important for many tasks in daily life. For example in sports, the magnitude, application and effectiveness of forces involved in a given task are a key factor for success. Likewise, in many situations, such as physical labour, loadings need to stay within safe limits to prevent injuries. To quantify the exerted forces on e.g. a hand, miniature force sensors are essential. Such a sensor must be accurate, with sufficient force range and capable of measuring forces in all directions. Moreover, the sensor must be small enough to be able to place it on a fingertip. In this thesis, the design, realization and characterization of force sensors which satisfy the aforementioned requirements is presented. The purpose of these sensors is to measure the interaction forces on the hand while handling objects. If this is combined with motion sensors which are also placed on the hand, an estimation of the mechanical power involved in a given task can be made. With such a system a given task can be optimized for optimal mechanical power transfer, which can for example be applied in sports or in rehabilitation in case a functional motor task involving physical interaction with the environment needs to be learned. The research described in this thesis can be divided in two parts: the realization of an accurate miniature force sensor and the realization of a capacitive read-out system for this sensor. The realized force sensor is fabricated in silicon and consists of two parts, a movable part which is mechanically connected to a fixed part by many thin silicon pillars. A force applied to the movable part results in a displacement which is measured capacitively using electrode structures. From the measured capacitances, the load applied to the sensor can be determined. By changing the number of pillars, their diameter and length, the sensor can be optimized for a given force range. This initial force sensor showed limitations in the design, and an improved force sensor design was made. In this new design a corrugated ring is placed completely around the movable part such that it seals the interior of the sensor ensuring that the electrode area cannot be contaminated. Furthermore, a part of the shear force exerted to the sensor will be carried by the ring, enabling a higher shear force range. For capacitive read-out, a reference capacitor is integrated in the force sensor, to compensate for common-mode changes in the sensor capacitance and for drift in the read-out electronics. The aforementioned sensors show good performance but their fabrication processes are relatively complex, therefore another force sensor is investigated which is easier to fabricate. The force range of this sensor is significantly smaller, but first measurements show that the principle is working. Further research is required to increase the force range of this sensor and to determine the ultimate accuracy that can be obtained. For read-out of the force sensor without the use of lab equipment, a small read-out system is realized which enables accurate measurement of the internal sensor capacitances. For this system a relaxation oscillator is used which is adapted such that it can measure differential capacitance. The noise performance of the oscillator in the system is analysed and measured, revealing the influence of individual component values on the noise performance of the system and providing a design guide for obtaining good noise performance. As a proof-of-principle the read-out system is interfaced with a force sensor and the measurement results are compared with measurements obtained from dedicated lab equipment. The complete system of the realized force sensor in combination with the capacitive read-out system is suitable for placement on a fingertip such that the forces exerted on a fingertip can be measured.

Towards a biomimetic gyroscope inspired by the fly's haltere using microelectromechanical systems technology

Flies use so-called halteres to sense body rotation based on Coriolis forces for supporting equilibrium reflexes. Inspired by these halteres, a biomimetic gimbal-suspended gyroscope has been developed using microelectromechanical systems (MEMS) technology. Design rules for this type of gyroscope are derived, in which the haltere-inspired MEMS gyroscope is geared towards a large measurement bandwidth and a fast response, rather than towards a high responsivity. Measurements for the biomimetic gyroscope indicate a (drive mode) resonance frequency of about 550 Hz and a damping ratio of 0.9. Further, the theoretical performance of the flys gyroscopic system and the developed MEMS haltere-based gyroscope is assessed and the potential of this MEMS gyroscope is discussed.