Month: June 2018

In this post, I’ll describe the process I use for sizing gearboxes and geared stepper motors.

To make the selection, I am using KEB’s software sizing program called KEB-DRIVE. KEB-DRIVE is free and easy to use. If interested to follow along, you can download a copy of the software.

2. Select the correct gear technology for the application
Configurations in KEB-Drive start at the top left. On the left, you’ll see drop-downs to select different gear types and sizes.

3.Motor Selection (Size, voltage, frequency)
Working to the right, I then select the size of the motor I want. Options for both Induction motors and AC Servo motors are listed. Here is a comparison of the advantages between servo and induction motors.

4.Adjust the Torque/Speed selection
Is it a speed reducer? Or a torque Increaser? It’s both – higher gear ratios will provide lower output speeds and higher torques. Use the drop down to see all the different possible configurations with the selected gearbox/motor combo.

5. What is the gearing Service Factor and why is it important?
The gearing service factor (SF) is the ratio between the:
A SF of 1.0 means the gears will have a nominal output torque equal to that of their rating. Selecting a motor/gear configuration with a SF of less than 1.0 is not advised. This means the gears will be undersized when operated at the nominal point. This could also indicate that the motor selected is too large.

6.Select gearmotor options (mounting style)
This section allows a user to select how the geared motor will be mounted. The flexibility of mounting is one reason that the KEB integral gearmotor solution has been so popular. Users can select a unit with an output shaft. Or a shaft mounted unit with a hollow bore. Mounting feet and mounting flanges can also be selected.

Geared stepper motors are perfect solutions for low speed and high torque positioning applications. GEMS provide NEMA size stepper motors that are paired with planetary gearbox and spur gearbox. Our design incorporates a square bodied motor and an round shape planetary stepper motor gearbox into a compact and cost-effective package. Our geared stepper motors are offered in six NEMA frame sizes (from NEMA 8 to NEMA 42) and each NEMA size motor has an integrated stepper motor gearbox with a wide range of gear ratios (from 1:3.7 to 1:369) so as to deliver any desired torque and speed combinations for your applications. The dual shaft version is available for you to install the brake, shaft coupler or an encoder where you need to keep track of the shaft position. 8-lead motor is aslo available upon request for all possible wiring configurations: bipolar, unipolar, series, or parallel. For higher speed and better speed control capability, please check out our brushless gear motors.

1.8° NEMA 8 GEARED STEPPER MOTOR WITH PLANETARY GEARBOX
NEMA8 is our smallest size of geared stepper motor. The 22mm diameter planetary stepper motor gearbox has gear ratio from 1:3.7 to 1:369. The gearbox output torque is up to 143 oz-in (1 Nm).

 

TABLE 1. MOTOR SPECIFICATIONS
Model Length L Rated Current Resistance Inductance Holding Torque Holding Torque Rotor Interia Lead wires Weight
mm A Ω/Phase mH/Phase Oz.in N.m g.cm2 g
17hs19-2004s 30 0.5 4.8 1.3 2.6 0.018 2.5 4 50
17hs162004s 42 0.5 7.5 2.4 3.6 0.025 4.5 4 90
TABLE 2. GEARBOX SPECIFICATIONS
Number of gear trains 1 2 3 4
Gear ratio 3.7, 5.2 14, 19, 27 51, 71, 100, 139 189, 264, 369
Length L2 mm 24.4 33 41.5 49.8
Rated output torque N.m 0.6 1 1.6 2
Max output torque N.m 1.8 3 4.8 6
Efficiency % 90 81 73 66
Weight g 35 45 55 65

First let’s explore how high performance closed-loop stepper motor system compare to traditional open-loop stepper systems in terms of torque and efficiency.

There’s superior performance from closed-loop stepper systems over open-loop setups as demonstrated in laboratory test results comparing the two systems’ acceleration (torque), efficiency (power consumption), position error (accuracy), heat generation, and noise levels. Just consider the relationship between torque and acceleration. Torque-speed curves show the peak and continuous torque ranges of a closed-loop stepper system alongside the usable torque range of an open-loop stepper system. Very often, torque in the real world translates into acceleration — so motors with greater torque can accelerate a given load faster.

To test this difference in torque performance in the lab, equally sized open-loop and closed-loop step motor systems get identical inertial loads. Programming commands the two systems to perform identical move profiles, except that acceleration rate and top speed are slowly increased in each system until they make positioning errors.

Here we have a move profile comparison between a open-loop vs. closed-loop system. This is a comparison between that from a StepSERVO closed-loop system and that from an open-loop system. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec2 and a top speed of 20 rev/sec (1,200 rpm)
as seen here.

Say that the open-loop system gets a maximum acceleration rate of 1,000 rev/sec2 and a top speed of 10 rev/sec (600 rpm). This top speed of 10 rev/sec correlates to where the flat portion of the torque-speed curve ends. The closed-loop system (due to its higher torque producing capability) gets a maximum acceleration rate of 2,000 rev/sec2 and a top speed of 20 rev/sec (1,200 rpm). This is double the performance of the open-loop system and cuts the move time nearly in half — from 110 msec down to 60 msec.

For applications requiring high throughput (such as indexing, edge guide positioning and pick-and-place systems) the closed-loop stepper motor driver system provides a clear performance advantage.

Amount, speed, and direction of rotation of a stepper motor are determined by the appropriate configurations of digital control devices. Selecting the most compatible stepper motor, driver, and/or controller, can save the user money and be a less cumbersome motion control solution. Anaheim Automation categorizes the major types of digital control devices as:

• Stepper Motor Drivers – offered in full-step, half-step and micro-step analog stepper driver
• Stepper Motor Controllers (sometimes referred to as Control Links – controllers indexers, and pulse generators sold separately or in Drivers Packs
• Stepper Motor Driver Packs – packaged units that include drivers and optional controller, with a matched power supply (most models are enclosed units that are fan-cooled)
• Integrated Stepper Motor/Driver/Controllers – packaged at the end of a stepper motor are drivers and simple controllers (only available for high-torque stepper motors)

These devices are employed as shown in Figure 5. The stepper motor driver accepts clock pulses and direction signals and translates these signals into appropriate phase currents in the stepper motor. The Indexer creates the clock pulses and direction signals, “translates” them into power to energize the stepper motor windings. The computer or PLC (programmable logic controller) sends commands to the indexer/controller.

Load characteristics, performance requirements, and mechanical design including coupling techniques must be thoroughly considered before the designer can effectively select the most suitable stepper motor and driver combination for a specific application. Failure to do so may result in poor system performance, or cost more than necessary. The following factors must be considered in order to obtain an optimum stepper motor motion control solution:

Why do you use a stepper motor?

The following safety considerations must be observed during all phases of operation, service and repair. Failure to comply with these precautions violates the safety standards of design, manufacture and intended use of the product(s). Anaheim Automation assumes no liability for the customer’s failure to comply with these requirements, and advises the misuse of its stepper motor products will void the warranty. Even well-designed and manufactured products, operated and installed improperly, can be hazardous. Safety precautions must be observed by the user with respect to the load and operating environment. Described briefly are general Safety Considerations. Please refer to the Environment Consideration’s Guide for more details.

•Use caution when handling, testing, servicing and adjusting during all phases of installation and operation of a stepper motor system
•No service/maintenance should be performed with power applied
•Exposed circuitry should be properly guarded or enclosed to prevent unauthorized human contact with live circuitry
•Stepper motor drivers/controllers should be securely mounted and adequately grounded
•Provide adequate air flow and heat dissipation for all stepper motor system components
•Do not operate a stepper motor system in the presence of flammable gases, dust, vapor or liquids

IMPORTANT NOTE: The customer is responsible for the proper selection, installation, and operation of the stepper motor products purchased from Anaheim Automation. The customer must determine the fitness of selected products for a specific application. Although it is the company’s intention to provide sound advice and accurate documentation, Anaheim Automation assumes no liability in the suggestions it offers.