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Tattoos have become popular worldwide because many people enjoy the form of self-expression that tattoos offer. Seeing them on our favorite pro athletes, musicians, and celebrities only adds to the popularity of this artform. Tattoos have even crossed over into the fashion and beauty industry.
Tattoos are symbols, images or drawings, permanently marked on the human body. This is done by reciprocating needles that repeatedly penetrate a person’s skin at a high rate of frequency, depositing insoluble ink with each penetration into the dermal layer of skin. A handheld tattoo machine uses a miniature motor that reciprocates the needle arrangement up and down in order to perform the penetration strokes.
The first prototype of a tattoo machine was invented and patented by Samuel F. O'Reilly. It was based on an electric pen invented by Thomas Alva Edison.
Types of Tattoo Machines
There are two types of commercially marketed tattoo machines: Coil Tattoo Machines and Rotary Tattoo Machines. They are named for their construction and the way the mechanism operates.
A coil tattoo machine utilizes an electromagnetic circuit to provide linear motion to the needle. Generally, a coil tattoo machine has one or more DC coils and spring points coupled with armature bar to move needle groupings.
A conventional rotary tattoo machine uses an electric motor with a rotating shaft having an offset cam mechanism at its end. The cam is coupled perpendicularly or axially with the mechanism to provide linear motion to the needle.
New Development in Tattoo Machines
Conventional rotary tattoo machines are trigger-activated, in which the cam-slider and motor assembly are perpendicular/aligned to the needle-armature assembly. Nowadays, pen type tattoo machines are in demand. In a pen type design, the mechanism and needle arrangement are in line in a cylindrical casing, offering an ergonomic design for the tattoo artist. Pen type tattoo machines are easy to maneuver. Also, manufacturers have been developing more efficient and compact machines, which are ideal for battery-powered applications.
In tattooing, there are three main inking strokes: lining, shading, and coloring. For lining, a single needle is used to penetrate the skin. Hence the throw need not be great to achieve proper skin depth penetration of the needle. For shading, which generally follows lining, a set of multiple needles is used simultaneously to penetrate the skin. Here, the throw given by the machine needs to be greater than the throw used for one needle lining strokes. The last type of stroke is coloring, wherein multiple needles, in a greater number than the number of needles used for shading, are used. For coloring, the throw needs to be greater than the throw used for shading strokes to achieve proper skin penetration by the needles.
To change the needle throw for a particular type of stroke, the tattoo machine must be adjusted. Effective tattooing requires change in the force, speed and depth. For this, many tattoo artists carry three tattoo machines set for each job; one adjusted for lining strokes, one for shading strokes, and one for coloring strokes. Having three separate machines eliminates the need for adjustments and speeds up the overall process. However, this arrangement is costly in that three machines need to be purchased, maintained, and cleaned after each job. New generation machines have a mechanism with added features that can adjust stroke, speed and forces which
allow one machine to cover all three strokes, in addition to being effective on all types of skin textures.
The new generation battery-operated machines being developed by manufacturers will be compact, lightweight, and portable. These can be used anywhere, at any location; a flexibility every tattoo artist dreams to have.
Typical Load Cycle of Rotary Tattoo Machine
Impact of Various Mechanisms on Motors
The motor is the driver of a rotary tattoo machine. The output load of tattooing is delivered directly to the motor through the specific mechanism.
In a cam-slider mechanism, the rotating motion is converted into linear motion, which reciprocates the needle at a high frequency and speed. During this operation, the cyclic radial load comes onto the motor shaft through the cam. This load is ultimately transferred onto the bearing which is at some distance from the cam. Based on the designed distance between the cam and the bearing, the radial load on the bearing is calculated and the motor is designed to withstand the radial load on the bearing.
In some rotary machines, a tapered cam and oscillating follower mechanism are used to convert rotating motion into linear, reciprocating motion. In this design, cyclic axial load comes directly on the bearing. Deep groove ball bearings are used in motors to withstand cyclic radial and axial loads. Preload is applied for rigidity and life enhancement of the bearings.
In tattoo machines, the dominant failure mode for motors is the bearing failure due to poor design of the mechanism or the wrong choice of the bearing for the amount of reaction axial or radial loads. This generally leads to the wear of bearing balls or one of the bearing races. The first indicator of a bearing failure in tattoo machines is either an increase in vibration felt by the artist or an increase in the motor noise due to the wear of bearings. In most cases, an increase in vibration is soon followed by an increase in noise until finally, the motor fails.
Bearing life associated with 90% reliability (L10) is as follows:
In a tattoo machine, the load is typically 3 N to 9 N. It acts radially or axially on the bearing depending on the nature of the mechanism. Also, there is constant axial preload of 1 N to 3 N acting on the bearing. The speed of the motor ranges from 4,000 rpm to 10,000 rpm. The life of the bearing is typically 1,000 to 1,500 hours, but it can vary depending on the mechanism, duty cycle, and handling of the tattoo machine.
New generation rotary tattoo machines are developed with additional features. In these, lining, shading and coloring can be easily done by adjusting stroke length (cam change), speed (voltage change) and force (spring force setting). These new feature settings are responsible for variable load amplitude with variable frequencies on the motor.
Essential Motor Qualities for Tattoo Machines
Cyclic radial and axial load due to working of tattoo machines is directly transferred onto the motor shaft and bearing inner raceway contact. This cyclic load causes structure-borne vibration and resulting noise of the motor, which is not desirable. If the reciprocating vibration in the machine is high, it generally results in damaging the skin.
It falls on the motor designer as well as the driving mechanism for proper selection of bearing, designing the mechanism for distributing the reciprocating load on the motor shaft, and preloading the bearing properly. The motor should have sufficient torque and speed, i.e. power, to get proper lining, coloring, and shading for good
quality tattoos. Insufficient speed and torque cause vibrations, which does not allow the coloring liquid to spread within the skin uniformly. This is because the pigment does not have the time to be absorbed by the epidermis when the tip of the needle reaches the end position. It is noted that to improve the diffusion of the color within the skin, the artist is often forced to apply more pressure to the tattoo machine and to incline it, increasing the penetration of the needle and accordingly the pain of the person receiving the tattoo, as well as causing trauma to the skin.
Motor regulation (R/K2) is the critical parameter of the motor which defines the speed torque characteristics. The lower the motor regulation, the more powerful the motor. As the torque (load) increases, the speed decreases. If the motor regulation is better, then there is less speed drop with the increase in load. This gives better stability for tattooing, as there is less speed variation with respect to load, resulting in less vibration and noise of the tattoo machine. Less vibration is desirable for good quality tattooing and healing. Also, there is less fatigue on the artist’s hand due to less vibration. Good motor regulation gives high power density of the motor, meaning less power losses and better efficiency.
Speed Torque Slope (∆N / ∆T) = (30000 / π) × (R / K2)
Efficiency is the critical parameter for next generation tattoo machines, which will be battery-operated. Higher efficiency will result in less power losses and less current consumption, which will increase the battery life.
The motor should be compact in size for proper ergonomics and handling of the tattoo machine. The motor should also be lightweight to reduce the overall weight of tattoo machine, which will give less fatigue on the artist’s hand over time. This will be beneficial for longer tattooing operations. A tattoo machine that is light and compact offers improved diffusion of the coloring liquid in the skin, simplifies the tasks of the artist, reduces the pain caused by the piercing action and increases its safety for the person being tattoed.
Tattoo applications require variable speed and torque, hence motor selection is critical. In the above generalized example, the 22S78 motor has the best speed torque characteristics, while the 16N78 motor has moderate performance within the smallest diameter. Similarly, the 17N78 motor offers moderate performance with moderate length and diameter. Optimized motor selection can be based on space constraint, i.e. available diameter and length, or by the motor performance. Portescap has launched new DCT motors, which can deliver increased performance.
Features in Portescap Motors Suitable for Tattoo Machine
In motors, the joint between the shaft and bearing is critical because of the cyclic axial and radial load of the tattoo machine. Portescap has developed optimized preloading of the bearing and the rigid shaft-bearing joint to withstand these load cycles. Hence, Portescap motors produce lower noise and increased reliability in tattoo machines.
Portescap offers miniature coreless DC motors in 16 and 22 mm frame sizes well suited for tattoo machines. Along with lower inertia and high acceleration capability, these motors offer better motor regulation and efficiency, as well as high power density and a good price to performance ratio, all in a compact and lightweight package.
Portescap motors are typically operated at high frequencies of 66-166Hz (4,000 - 10,000 rpm) and can go for even higher frequencies. Customization is available to meet customer requirements, including for the shaft, mountings, connections, aesthetics, and many more features.
Conclusion Tattooing continues to grow in popularity every year, hence rotary tattoo machine manufacturers have been developing new machines with additional features to improve and enhance the process. The most critical aspect of these new machines is the motor. It should deliver the required performance, as it is the prime mover — sustaining all the reciprocating loads created by the mechanism. Motor performance and reduced noise should also be considered, as these are the key quality parameters for motor and machine reliability.
As new generation machines continue to develop, so too does the demand for motor customization. Compact and lightweight motors with high power density are at the heart of every new generation tattoo machine.
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