Inductive Position Sensing With Single Coil Elements

Gill Sensors & Controls Ltd. Inductive Position Sensing with

Single Coil Elements

Gill Sensors & Controls Ltd & Industrial Electronic Controls Inc.

• Inductive Position Sensing Technology & Working Principle

• Industrial Application in Production Volumes

• Present basic working principles of an inductive position sensing technology

• Introduce performance differentiators with this technology’s ability to:

Be immune to thermal shifts

Tolerance to local magnetic interference

Achieve true absolute position

Tolerate mechanical misalignment in the mating mechanical assy.

• Provide details on an existing Industrial pedal application where mechanical play was of concern (IEC)

Gill Sensors & Controls Ltd / IEC

Industrial Electronic Controls designs and manufactures a variety of foot pedal, joystick and sensor products to suit multiple industrial control applications

Gill Sensors is a leading UK based manufacturer of sensors used in Construction, Agriculture, Motorsport, Defense, Marine and Material handling industries. Products include: non-contact rotary and linear position sensing, liquid level sensing, oil condition monitoring and fluid flow sensing

Original Equipment Manufacturers End Usage

Jon Klein – Vice President Engineering Industrial Electronic Controls

Paul Cain – Manager New Business Development, North America

Co-Authors

• Present basic working principles of Gill’s single coil inductive technology

• Introduce Technological Differentiators with Gill’s ratiometric properties with the second, third, coil:

Immune to thermal shifts Ability to achieve true absolute position Tolerance to mechanical misalignment in the mating

mechanical assy.

• Provide details on an existing Industrial application

where mechanical play was of concern (IEC)

Gill’s Inductive Position Sensor

Pulse Induction Metal Detector

Inductive Loop Traffic Sensors

Working principle of inductive coil technologies

The target (or activator) is simply a piece of mild steel with a specific shape

Three basic components: the coil, the target (activator) and Gill’s proprietary signal processing electronics.

Gill’s Single Coil Inductive Position Sensing Technology

Present basic working principles of an inductive position sensing technology

A1-Activator

C1 -Coil

P1 -Processor

Current Day Standard Product

Step 1 The processor sends a known pulse of energy to the coil, (Gold Trace). This results in a magnetic field radiating across the airgap

Step 2 The processor then switches modes and using the same coil, prepares for receive mode. This is a ‘settle’ state, noting the switch position

This pulse of energy is absorbed by the mild steel activator in the form of eddy currents

Step 3 The processor then switches modes and using the same coil, now in receiver mode, begins to measure the remaining energy that resides in the activator

Steps 1 and 3 showing transmitter mode (Gold) pulse and receiver mode (red) pulse.

Step 4 the processor measures these two eddy current levels, along with the

time duration, comparing these two residual eddy currents. Reading To and T1

t0 t1

Step 5 The processor compares the two eddy current levels and arrives at a specific amount of eddy current decay in the activator.

Knowing these two energy states, the processor calculates the size of the energy drop, plus the known time delay and calculates the current position of the activator

T0 T1 T6 T7 T4 T5 T2 T3

Changes in Activator position are monitored over 1,000 times per second

Each new position of the Activator has a unique slope in eddy current decay (red curve)

Each of processor iteration results in a new position in linear activator movement

Adding a second coil brings ratiometric properties to the sensor

A 2 coil design improves: -Temperature stability -The ability to calculate absolute position and direction -Mechanical tolerance immunity -i.e. uncontrolled movement in other axis -Susceptibility to outside magnetic influences.

A1-Activator

C1 & C2 Coils

P1 -Processor

DUAL COIL DESIGN Both Coils need to be observing eddy currents from the (single) activator

The processor begins storing and comparing both coil results.

Both coils will be reading the decayed energy for the exact same duration but in sequence of C1, C2, C1, C2, etc).

T0 T1

T2 T3

The design effectively ignores temperature fluctuations The processor ‘knows’ both coils are reading a target that is the same temperature, by observing the same target, hot or cold, any relative change in energy state has to be a change in position, not a temperature induced energy change.

Definition: Absolute Position is the inherent characteristic of a position sensor to

know its true location at power on / off / on. When turned back ‘on’, an absolute sensor begins broadcasting its actual position without requiring any movement or triggering of an index pulse or any reference positioning. This absolute characteristic applies even when the sensor has been moved during the ‘off’ event.

The design’s tolerance to misalignment in mechanical sub-assemblies





Two main components in Gill’s 1st Generation Inductive rotary angle sensor

Dual Activators on a shaft Sensor Electronics & Coils The Complete Assembly

https://youtu.be/z--K8PBfK38?t=89

Video of Gill Gen I Dual Cavity Sensor

Jon Klein Vice President of Engineering Industrial Electronic Controls Inc.

Design characteristics that are typical in an existing Industrial pedal application where mechanical play was of concern (IEC) -Long cycle life -Heavy side loading -Bearing wear -Possible location close to large electric motors -Tight packaging constraints -High importance on robustness and reliability

Application History on a Steering Column Mounted Pedal Assy (Industrial Vehicle)

Decision criteria in selecting a rotary angle sensor

-Tolerance to misalignment over lifetime -Environmental sealing without bearings or rotary seals -Unit price -Independent Outputs -End of shaft style sensors -Elimination of (internal) return springs as an anti-hysteresis compensator -fewer parts = fewer failure modes -broad input voltage range +5V to +48V

Exploded view of full pedal assembly

1- There are 2 bushings pressed in the arms This pressing operation allows for the possibility of mechanical misalignment 2- When the Pivot Tube is tightened down it reduces the axial movement of the other components.

Exploded view of full pedal assembly

4- There are 2 weld bushings -one on each arm. The bushing’s final positioning at the weld operation can contribute to activator misalignment 5- The separation washer thickness is used to control the minimum gap between the two arms.

Return Spring

Brake Pedal Arm (section view)

Bearing

Nut & bolt compressing sub assy.

Inductive Coils

Moving activator 1 Moving activator 2

2 bushings / pedal

Pivot tube

Width of the mounting bracket tolerance allows for the arms to slide on the pivot tube.

Summary

-Designing for end-of-life mechanical conditions -High tolerance to misalignment -Independent outputs -Ignores large magnetic interference -Withstands high pressure water blasting