Frequently asked questions and their answers

Motors FAQ

What is holding torque vs. dynamic torque related to a stepper motor?

Holding torque is the maximum restoring torque developed by the rotor when one or more phases of the motor are energized. The dynamic torque is called running torque or pullout torque. It varies at different speed by different driver technologies and power input. As a rule of thumb, the maximum dynamic torque is about 70% of the holding torque.

What are some advantages of Using Stepper Motors?

A wide range of rotational speeds can be utilized since the speed of a step motor is proportional to the frequency of the input pulses from your controller. Precise open-loop positional control is possible with a stepper motor without any feedback mechanism. Very low speed rotation is possible with a load that is coupled directly to the shaft of the stepper motor. A stepper motor is quite reliable because there are no contact brushes. Generally, the life of a stepper motor is determined by the life of the stepper motor bearing. A stepper motor is very good at starting, stopping, and reversing direction. A stepper motor provides precise positioning and repeatability of movement. An energized stepper motor maintains full torque at standstill position. These are some advantages of open loop steppers.

A stepper motor can also be used in closed loop which you give even more advantages. If you like to know more about that, let us know.

What is Micro-stepping?

Micro-stepping is used to increase a motor’s step resolution. This is achieved by controlling the motors phase current ratio. It should be noted that micro-stepping does not increase step accuracy. Micro-stepping will allow a motor to run smoother and with less noise. The degree of the improvement depends on the step accuracy of the motor.

Can BLDC motors run as servo motors?

We do not recommend using BLDC motors as servo motors because BLDC’s run better at high speeds and cannot handle slow, precise movements. For an application requiring low speed and accurate positioning, we recommend using a stepper motor and an encoder.

Advantages of Using Stepper Motors

A wide range of rotational speeds can be utilized since the speed of a step motor is proportional to the frequency of the input pulses from your controller. Precise open-loop positional control is possible with a stepper motor without any feedback mechanism. Very low speed rotation is possible with a load that is coupled directly to the shaft of the stepper motor. A stepper motor is quite reliable because there are no contact brushes. Generally, the life of a stepper motor is determined by the life of the stepper motor bearing. A stepper motor is very good at starting, stopping, and reversing direction. A stepper motor provides precise positioning and repeatability of movement. An energized stepper motor maintains full torque at standstill position.

Can different voltages be applied other than the specified voltage?

Yes, you can apply different voltages, although, you must keep in mind that there is a speed limit for the bearings. If you increase the voltage, the speed will increase. If you decrease the voltage then the speed will decrease. For example, if a Brushless DC Motor is rated to run at 3000 RPM no load with 36VDC, the motor will run 2000 RPM with24VDC. The maximum speed, torque, and power are directly proportional to the voltage.

``1.8 degree or 0.9 degree? ``

Step accuracy is the primary character of a step motor. Without step accuracy, the motor is useless. Based on motor manufacturing capability, step accuracy is rated at +/- 5{e65dbe2062fe22c6bb4e101c6a8bc9461e141c3a60762ef3ae68342553e91163} of the full step. That means a 1.8-degree motor would have step error of +/- 5.4 arc minutes, while 0.9-degree motor would have step error at +/- 2.7 arc minutes.

This is because the motor step accuracy is determined by the torque stiffness, and the torque stiffness is determined by maximum holding torque and the number of rotor teeth.

Motor torque function: T(θ) = To*Sin(Nθ)

Torque stiffness: dT(θ)/d = N*To*Cos(Nθ)

(where To=maximum holding torque, N=number of rotor teeth, θ=rotor displacement)

A 1.8-degree motor has a 50-tooth rotor and 0.9-degree motor has a 100-tooth rotor. With the same manufacturing capability, a 0.9-degree motor will have twice the step accuracy of a 1.8-degree motor.

What is the difference between Unipolar and Bipolar drivers?

A Unipolar driver’s output current direction cannot be changed. There are two sets of the coils for each phase in a unipolar wired motor, and only one set of the coils can be energized at a time. Each coil represents one phase. Therefore, only 50{e65dbe2062fe22c6bb4e101c6a8bc9461e141c3a60762ef3ae68342553e91163} of the winding is utilized in the unipolar drive. Therefore, all of the windings are utilized because the same coil is used for forward and backward current direction. The motor wiring does not have to be changed to change the direction of a motor using a bipolar driver.

Do Hall Sensors need to be used to drive a Brushless DC Motor?

Hall sensors use feedback to tell the motor driver which phases to turn off and on, which is required for motor operation. However, an encoder can be used in place of a Hall sensor to provide this feedback, so technically a Hall sensor is not required if an encoder is used instead.

What does it cost to solve a driving issue?

Regularly we get the question: what will it cost? This question is not easy to answer. In order to work out a suitable proposal for a driving issue, many things have to be taken into account. For example the type of motor technology that can be applied: a stepper motor is more cost-effective than a high torque direct drive motor. Or the degree of protection against dust and moisture, the so-called IP value. The higher the required degree of protection, the more expensive the solution. By saving components, you can of course also save on costs. Therefore we always look at the drive issue as a whole of the application so that we can think along with it.

Do you have servo motors with UL certification ?

Yes we have. In our product range we have brushless servo motors from 40-80mm (up to 1000 Watt) with UL certification. On request we can send the Certificate of Compliance with all partnumbers inside. Motors can be marked with the UL’s Recognized Component Mark.

Gearboxes FAQ

Where can I find the breakaway torque values for Thomson's Micron gearhead products?

We do not specify breakaway torque values for our standard Micron gearhead products. We can offer gearheads to meet particular breakaway torque values as a special option. If your application requires a specific breakaway torque value, please contact our Application Engineering team for further assistance.

Mechanical FAQ

Are actuators suitable for wash down environments?

The IP rating of an actuator is a good indicator of how suitable it is for various environments including wash down. The minimum to consider out door or light wash down use is IP65 which can stand low pressure water jets from any direction. The next level is IP67 which will keep out water when submerged in 1m of water and NOT running. Finally, IP69K is the best and will keep out water from high pressure jets and immersion.

What should be used to lubricate linear bearings and how often should they be lubricated?

Lubrication is a very application specific topic and usually, linear bearings are compatible with a wide variety of lubricants on the market. Lubrication specialists can give recommendations for demanding applications but in general we advise:

  • Light loads and high speeds do well with a machine oil or low viscosity grease.
  • Medium loads and speeds do well with NLGI 1 or 2 grease.
  • High loads may require a grease with an EP2 additive. The EP is Extreme Pressure and uses special additives to prevent the grease from breaking down under high pressures. This type of grease will give the steel shafts a dull appearance.

Careful monitoring of the application is required to develop a good preventative maintenance schedule. The shafts should be kept with a slight film of grease/oil at all times. It should feel slick to the touch, but not dripping.

Linear slide tables should be lubricated per the manual, using a different grease that what was supplied at the factory can cause the grease to degrade. DO NOT use any type of dry lubricant (PTFE powder, graphite powder, etc.) with any recirculating ball or roller type of bearing. While these lubricants are good for sliding motion, they do very little to aid rolling friction.

What’s the best way to balance load capacity vs. machine life?

The higher the load, the shorter the life for a given capacity bearing. By choosing a different bearing you can positively impact/balance that relationship to suit your application. The geometric envelope is also important, which limits the choice of possible bearings for the application.

How do you prevent premature wear from misalignment of the rail system and drive screw?

Obtaining proper alignment is essential for preventing premature wear. Proper alignment is achieved as the result of either of the following two methods:

  • Design an inherently aligned system by controlling tolerances that rigidly locate the components.

OR

  • Address alignment during the assembly process by following good installation guidelines.

For either option, be sure to contact our application engineers.

What environmental factors impact linear guides and eventually machine life?

An environment’s corrosiveness, humidity level, contaminants, airborne particulates, chemical compatibility, unpredicted (variable) impact loads, wash down, and many and many other factors should all be considered when determining the speed, accuracy, acceleration and travel distance of your linear guide. Know the environment well and consult with experts to predict the impact of your application’s environment.

What sort of applications would lead screws be used in?

Lead screws are often used in instrument grade applications where smooth, precise, clean, and maintenance free operation is required. The nut material is typically made of an internally lubricated polymer. Some examples would be laboratory and life sciences equipment such as DNA sampling, scanning and fluid handling devices.  Other applications include engraving, rapid prototyping, inspection, and data storage. Lead screws are also used in heavy lifting applications when combined with a metallic (typically bronze) nut.

How can bearing preload impact maximum application yield and machine life?

The higher rigidity obtained with preload can improve yield and accuracy; however, this could also shorten the machine life.

How do you control installed costs for a given accuracy requirement?

Don’t overspend by defining higher accuracy than is required for your application. For example, a round rail may do the job in applications often specified to use square rail. Contact our application engineers to you ensure you don’t over design for your application.

Why is my PPA actuator making a loud noise?

The clutch design sometimes causes this to happen with the PPA line. The tolerances in the clutch are such that they will sometimes make a squealing noise with helping loads (like lowering a heavy object). The clutch will still function correctly but there is no way to prevent this noise if that particular actuator makes it. The sure fire solution is to use a different actuator with helping loads. The PPA does not make this type of noise with compression loads.

How does the mounting surface choice impact installation time and total machine cost?

The more accuracy you need, the more time and expense will be required to prepare the mounting surface. Choosing round rail over profile rail can significantly reduce the need for expensive mounting surface preparation. Make sure to specify only the accuracy and rigidity needed for your application to limit your costs.

How can you accurately predict the effect of load orientation on maximum load capacity?

Round rail is highly impacted by load orientation, while Profile rail has less sensitivity to orientation.

Drives & Controllers FAQ

Can Galil controllers be operated ``stand-alone`` without a computer?

Galil offers motion controllers and PLCs with RS232, USB or Ethernet connectivity which are designed to sit outside of the PC bus. After initial programming and downloading of a motion program into non-volatile memory they can operate without a host computer. Galil’s Ethernet/RS232 DMC-40×0 box-level controllers are packaged with drives in a rugged, metal enclosure. The DMC-41×3 and DMC-21×3 Ethernet/RS232 series are card-level or DIN rail mount controllers.

Can motion controllers work with non-linear systems?

Yes our controllers can work with non-linear systems. This is possible using various approaches including two sets of PIDs as well as changing PIDs on the fly, also called gain-scheduling.

I need to display the position of each axis continuously. Doesn't this tie up the controller?

Galil controllers provide a secondary FIFO buffer which captures real-time data such as position, torque and error continuously. This buffer can be transmitted continuously over PCI or UDP/IP. Accordingly, the host PC does not have to poll for this data and other communications are taking place through the primary communications FIFO buffer. Galil’s software tools provide a real-time display of important motion data such as position, velocity and torque.

Can motion controllers work with non-linear systems?

Yes our controllers can work with non-linear systems. This is possible using various approaches including two sets of PIDs as well as changing PIDs on the fly, also called gain-scheduling.

What are the features of DMC code?

DMC code is an easy-to-use, high-level programming language that has been continually developed and improved since 1983. It is particularly well suited for motion and I/O applications including event-driven execution, motion and I/O trip points, local scope variables, subroutine stacks, conditional statements, mathematical functions and multi-threaded execution.

I like screw terminals, but I want to be able to detach them easily for servicing. How can I do this with the RIO?

If you choose a RIO with screw terminals (RIO-472xx, RIO-473xx), you will not be able to detach them for servicing but will have to unscrew each wire. With the RIO-471xx you can use the ICS-48044m and the ICS-48026m. This allows you to have screw terminal connections and then you can simply detach these 2 boards for servicing.

Can I communicate to various industrial Ethernet protocols such as EtherCAT, Modbus and Ethernet/IP?

Yes. The DMC-50xx0 is an EtherCAT master that can be connected to various slaves. All Ethernet products support Modbus. Additional protocols such as Ethernet/IP and Modbus RTU are available as firmware customizations.

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