Torque Wrench / Gauge Tactile / Haptic (vibration) Feedback
Abstract
Over the next decade, a great number of industrial instruments and tools will use vibration and tactile (haptic) feedback to augment the traditional indication methods of light and sound.
Users, operators, and buyers of products are familiar with the benefits of vibrating tactile feedback from its ubiquitous use in mobile phones.
Haptic feedback can add product value and differentiate products against competitor offerings. Market leaders in the world of electronic torque wrenches have already started to integrate haptic / tactile / vibra / vibration feedback into their designs.
We present an application note offering a detailed guide on how to integrate a vibration feedback functionality into torque wrench tools and products with a similar form-factor.
Background
Electronic torque gauges are used on the factory floor in many industries, to ensure that fasteners are tightened sufficiently. The electronic versions offer a number of beneficial features over the mechanical types, which has fostered their adoption to become widespread. One of the most important features is the feedback to the operator that a preset torque has been reached.
Almost all digital torque wrenches on the market contain an audible alert that the correct torque has been reached. In addition, some contain an optical indication as well, usually in the form of a multi-colour LED. In noisy environments, or places where the tool is used with reduced visibility of its user interface, it is possible that neither of these alerts are sufficient to notify the operator.
A neat solution to this problem, and one that adds value and a competitive advantage, is to integrate a miniature vibration motor to the product. The benefits of vibration feedback are well know to all of us who use a mobile phone. But they are also becoming more common in production environments as tool designers address the needs of users, who need a reliable and positive confirmation that an alert event has occurred.
Vibrating feedback is ideal for this function as the frequency and amplitude of the vibration motor can be tuned so as to offer an alert that simply cannot be confused other alerts, i.e. similar sounds or illuminations generated in the near environment. The vibration feedback is immediate, positive and localised solely to the operator using the tool, which makes it a superior alternative to traditional visual or audible alerts.
Integrating a vibrator motor into the design is relatively straight forward assuming there is a small amount of free space in the enclosure. We have presented a number of suggestions using different shaped motors to make the design integration as fast, cheap and easy as possible.
We present below, a series of reference designs and suggestions for how a designer would include a haptic 'vibra alert' into an electronic torque wrench. The text below contains a summary of the principals of operation and design, and a walk-through guide of the areas that need to be considered to conclude a successful design.
Principals of Haptic (Vibration) Feedback in Digital Torque Wrenches
The general principal is simple. An eccentric mass motor (vibrating motor) is mounted within the digital torque wrench. A line from the embedded microprocessor drives a MOSFET that turns the motor on / off whenever an alert condition is reached.
The closer that the vibration motor can be placed towards the handle of the digital torque gauge, the better. Vibration can be made to penetrate protective clothing (e.g. gloves) by selecting a motor that offers lower frequency vibrations; cloth and foam padding will attenuate higher frequency vibrations to a greater extent.
Consider the Z axis to be the length of the torque wrench as demonstrated in the diagram below. Placing the vibration motor so that its shaft is along the Z axis will ensure that all the vibration displacement energy is distributed in the X and Y planes; i.e. into the operators hand as it grips around the end of the wrench.
The maximum vibration will be felt by the operator when vibration motor's eccentric weight is in the centre of the hand's gripping position. Typically the batteries will take up space here, so some compromise will need to be sought depending mostly on the enclosure. For this reason, we present three general layouts below for adding a vibration motor to this generic design.
Selecting The Most Suitable Vibration Motor
Method 1. Cylinder (Bar) vibration motor
The greatest vibration intensity will be generated when a regular cylindrical style vibrator motor is mounted with direct and firm contact to the enclosure. This will allow the use of a wide range of vibration motor types from Ø4mm up to Ø24mm, and offer the widest possible range of frequencies and amplitude. Flying leads (possibly with a connector) will be required to connect the motor to the main PCB. This is the 'gold plated' solution and best considered as part of a new design.
Cylindrical vibration motor part suggestions:
| Part Number | Motor Description | Product Page |
|---|---|---|
| 307-002 | High-output 1.5v 7mm cylindrical vibration motor | 307-002 |
| 310-001 | High-output 1.5v 10mm cylindrical vibration motor | 310-001 |
| 312-105 | High-output 3v 12mm cylindrical vibration motor | 312-105 |
| 312-107 | Low-frequency 3v 12mm cylindrical vibration motor | 312-107 |
If retro-fitting an existing design - consider one of the alternative methods below.
Method 2. Shaftless (coin) vibration motor
An alternative to method 1 is to add affix a coin / shaftless vibration motor to an internal bulkhead (if one exists). Our shaftless vibration motors contain a strong self-adhesive pad which makes for simple assembly. Ideally the coin motor would be mounted perpendicularly to the Z axis so as to send its vibration energy in the X and Y planes. If this isn't possible an alternative would be to attach the coin motor to a space on the PCB, on the X plane, though in this case nearly all the vibration energy sent into the Z axis will be lost, and could further irritate the torque transducers producing unwanted noise.
Our shaftless (coin) vibration motors come with integrated 45mm flying leads as standard, though we can alter the lead length and arrange for a wide range of connectors to be added to make PCB assembly easier.
Shaftless (coin) vibration motor part suggestions:
| Part Number | Motor Description | Product Page |
|---|---|---|
| 308-100 | 8mm 3v Shaftless (coin) vibration motor | 308-100 |
| 310-103 | 10mm (slim profile) 3v Shaftless (coin) vibration motor | 310-103 |
| 310-105 | 10mm (lead-less) 3v Shaftless (coin) vibration motor | 310-105 |
| 312-101 | 12mm 3v Shaftless (coin) vibration motor | 312-101 |
| 312-103 | 12mm (slim profile) 3v Shaftless (coin) vibration motor | 312-103 |
| 310-113 | 10mm 3v Shaftless (coin) vibration motor | 310-113 |
If there is no free surface onto which to affix the coin vibration motor, consider a PCB mounted motor instead.
Method 3. PCB mounted vibration motor
A final alternative to methods 1 and 2 is to mount the vibration motor directly onto the PCB (enlarging the PCB if there isn't enough space). The nice thing about this approach is that it may not require any modifications to the enclosure.
Like the other vibration motors, it is far better to place the PCB vibration motor with its shaft along the Z-axis, and with the eccentric mass as close to the handle as possible. We have several PCB mounted types including through-hole, press fit and surface mount SMT reflow vibration motors, as well as through-hole mountable motors with flying leads.
PCB mounted vibration motor part suggestions:
| Part Number | Motor Description | Product Page |
|---|---|---|
| 304-005 | 4mm 1.5v through-hole & leaded PCB vibration motor | 304-005 |
| 304-008 | 4mm 1.5v surface-press PCB vibration motor | 304-008 |
| 304-109 | 4mm 3v SMT reflow PCB vibration motor | 304-109 |
| 306-006 | 6mm 1.5v through-hole PCB vibration motor | 306-006 |
| 304-111 | 4mm 3v through-hole & leaded PCB vibration motor | 304-111 |
| 304-108 | 4mm 1.5v surface-press PCB vibration motor | 304-108 |
Having found the most suitable motor, please also consider the following factors:
Drive Voltages
Depending on the design and battery types, there may be a variety of bus voltages in use. Since the majority of processor driven applications are run from either 1 or 2 alkaline or NiMH cells, or a single lithium ion cell, most of our motors are wound to run on either 1.3v or 3.0v nominal voltages with a capacity to be over voltage-wise driven by 20%. For customers running on 3 or 4 cell designs it's best if you get in touch with one of our support engineers. We can produce certain motors wound to higher nominal voltages which would remove the need to introduce voltage-drop circuitry into the design.
Customisations
Our range of motors can be customised to requirements. A good place to start is our vibration motor customisation guide to get a understanding of what's possible. Then contact our design support team to can advise what's possible and pricing.
The Integration Process
We have a lot of experience in helping customers integrate our parts into their product designs. During this time, we have developed a process that we follow internally to help guide customers to the most suitable part.
The diagram below summarises our suggested process by which to update an existing design to incorporate a vibration motor for haptic feedback.
We split it into the following three areas to consider;
- Mechanical design to mount the vibration motor into the products enclosure,
- Electrical design to ensure that the motor is driven correctly,
- Software design to ensure that the drive circuitry is fed with the correct signals.
We have application specialists with masters level degree training in each of these areas who will be happy to help.
Mechanical Design
The feasibility to modify the enclosure, will dictate which kind of motor is chosen for the application. Our white paper on mounting vibration motors offers a detailed explanation of the factors that should be considered. Essentially though it bottles down to whether or not the enclosure is modifiable, whether there are any flat surfaces within the enclosure, and if neither of these are true, the final option is to use a PCB mounted vibration motor.
Electrical Design
Once the mechanical design is accomplished, it is necessary to add a small drive circuit to shuttle power to the vibrating motor. This is relatively simple, and our white paper on driving vibrating motors has detailed suggestions for areas that need to be considered and reference designs. The drive circuitry can be driven from an existing signal to say an LED, or buzzer, or it could be driven with a spare line from the host processor (if one exists in the application).
Software Design
Once the motor is mounted and the circuit is completed, the final thing to consider is whether a processor will be sending the drive signal to the drive circuitry. If so, and depending on the software implementation on the processor, it may be worth modifying the code to provide some more complex haptic feedback to the user.
Application Summary
In this application note, we have put forward the case for there being a natural demand for the introduction of vibration based tactile (haptic) feedback into tools like torque wrenches.
These tools rely on sending a dependable, instant and clear alert signal to the operator. Vibration feedback is a great way to augment traditional alert methods of light and sound.
Precision Microdrives offers a wide range of inexpensive vibration motors with next day availability that can be easily integrated into existing and new designs.
We have presented a simple 3 step integration process and recommended parts that would be suitable for 3 different design implementations.
Vibration Tactile feedback can add product value, and differentiate your products from your competitor's offerings.
Next Steps
We may not have been able to answer all of your questions, and it's possible that we've prompted further questions than you originally had.
No problem - we're here to help. Please feel free to contact our design support team or commercial team if you need any further support. Our support engineers have a wealth of engineering, manufacturing and application experience and will be only too happy to support you at every stage of your design and manufacturing process.
Alternatively, if you want to start prototyping, please visit our online store where you can buy 1+ quantities of a wide range of vibrator motors on same-day dispatch.
If you're an international customer and want to order some samples - that's also no problem, and we can ship to most parts of the world via economic tracked airmail, or 1~3 days via UPS.
