For certain low-power applications, where inherent control is simple, micromotors and drivers, and high-density torque stepper systems constitute a viable option for servo motors. Stepping is the only motion control method that can operate in an open-loop manner without position feedback. This makes stepper motor systems much simpler than servo motion systems, and the lower cost also adds to the attractiveness of stepper motors. Coupled with other continuous design improvements, such as hardware miniaturization and high-density torque, stepper systems remain highly competitive in many motion applications requiring lower speeds and positioning accuracy. Stepper-based motion systems can achieve power outputs of 0.75 kW (1 hp), but most applications operate at lower output power. A large number of manufacturers are focusing on this market. [ALIGN=CENTER] Baldor Electric's NextMove e100 real-time motion controller can interpolate for 16 axes and manage up to 240 axes connected to an Ethernet Powerlink. These axes handle simple point-to-point motion, guided sequences, jog control, and the torque requirements associated with stepper (servo) motion systems. [ALIGN] Size and Functionality Issues: Parker Hannifin believes that small size and ease of operation are significant advantages of stepper systems, while low price is another advantage that allows them to compete with servo motion systems. "Stepper systems can be made very small without increasing costs," says product manager Marc Feyh. "There are some miniature servo systems, but they are not that small, are more expensive, and require even more miniaturization of components." Simple open-loop operation is its second advantage. However, competing on a price/performance basis is becoming increasingly difficult. The goal is to continue improving size while maintaining performance at a "reasonable price." Parker points out that this trend differs from expensive high-end stepper systems, which cannot compete with low-priced servo systems. To meet size and cost requirements, Parker's electromechanical automation division is introducing a stepper drive/controller, a miniature stepper unit that provides a programmable controller and integrated input/output ports. A palm-sized pre-installed unit (1.1 × 1.5 × 4 inches) mounted on Parker's Promech series linear driver constitutes a miniature stepper motion system. The Park rotary stepping amplitude has been reduced to NEMA 11, 14, and 17, translating to 1.1, 1.4, and 1.70 inches per face in the cross-section of the square motor, respectively. According to Shinano Kenshi Corp. (SKC), miniaturization, high-density torque, and low noise/vibration are key improvements related to stepper motion control. SKC proposes that the price of the stepper motor should be controlled (reduced) while making these improvements. It is claimed that new or redesigned rotor and stator laminations have optimized the internal space and structure of the NEMA 17 and 13 stepper systems. The redesigned stepper system has 20%-30% higher operating torque than previous SKC models, using the same input power and cost-effective permanent magnet materials. Rex Bergsma, chairman of SKC (US), explains that the improvement involves adding additional permanent magnet material to the rotor. Since the total space is fixed, the location of a certain stator position, i.e., the phase winding location, needs to be moved. The redesigned laminations have also improved the tooth profile of the rotor and stator of SKC's new STP-430 stepper motor. The result is a stronger, more concentrated magnetic field, reduced noise (see figure) and “set-up time (damping), nearly twice as fast as the previous model,” Bergsma said. Not Just Rotary In addition to traditional rotary stepper motors, linear stepper motor systems also exist. Baldor Electric says application and design engineers are increasingly interested in these linear motion products. It cites the advantages of rotary motors (servos), such as fewer parts, minimal wear or maintenance, and ease of integration into machines. “Linear stepper motors are well-suited for applications with light loads, offering excellent open-loop performance, higher acceleration, and higher speeds than rotary motors,” said John Mazurkiewicz, product manager at Baldor. Baldor manufactures a wide variety of linear stepper motors, including single-axis, dual-axis (X, Y axis) units, multi-axis gantry motors, and customer-designed models. The company’s NextMove series of programmable controllers provides the appropriate output power to operate linear and rotary stepper motors (as well as servo motors). Real-time motion controllers are the latest NextMove products (see photo). Oriental Motor states that the development of new stepper motors and drive systems is "a process of improving performance parameters and integrating components." This process comprises several trends: ■ High-density torque: Regular redesigns using neodymium iron boron (Nd-Fe-B) rare-earth permanent magnets with higher energy density, coupled with structural changes such as larger rotor diameters, have improved motor torque performance. Benefiting OM products include the high-torque PV and PK-HT series hybrid stepper motors (2-phase) and the CRK series, five-phase motors. ■ Improved step angle accuracy and drive smoothness: An advanced microstepping method achieves higher stepping accuracy by controlling the current. For example, Oriental's RK series five-phase micro-drivers combine a special ASIC, proprietary software, and current sensors to control the current over a wide speed range. The current sensors and control software further ensure "smooth drive functionality," suppressing vibration and noise during operation, independent of the driver's input frequency, explains Nick Johantgen, Engineering Manager at Oriental Motor USA. Five-phase stepper motors, with their inherently lower vibration, are the opposite of two-phase stepper motors, which also benefits this situation. Products with "smooth drive" include five-phase stepper motor control in PK and CRK systems. ■ More Miniaturization: "Miniaturization is the general trend for open-loop stepper motors and their associated drivers," says Johantgen. "Portable medical and industrial instruments require smaller motors in many applications." To meet this requirement, OM has developed 8-inch and 11-inch CRK five-phase motors and 11-inch and 14-inch (1.4 in./35 mm) PK two-phase stepper motors. The new compact CRK microstepper driver measures only 0.98 x 1.77 x 2.56 in and can control up to 1.4A of CRK motor per phase. Systems and Market Analysis: Another intention of Oriental Moto is to integrate various stepper motor/driver components into a system solution. This includes mounting plates, flexible couplings, vibration dampers, and controllers. "Integrating the components into a complete system is to reduce the overall cost," adds Johantgen. It further enhances and servo motion competitiveness. The system also offers three types of gear heads for the CRK stepper motor. Lower-cost hobbing gears have a backlash of 10-35 radians (related to gear ratio); planetary gears have a wide range of gear ratios and a backlash of 3 radians; harmonic gears essentially eliminate all backlash. The overall size of the stepper motion market, including the commercial and automotive industries, is quite large. According to the latest market research from Motion Tech Trends (MTT), the core industrial sector, factory automation (FA), represents a relatively small but solid market, with stepper motor and control consumption in North America reaching approximately $1.56 million in 2006. The FA market includes machine tools, robotic systems, and production machines for various OEMs (including semiconductor equipment, printing, textiles, plastics, etc.). According to MTT's rough estimates, Europe and Japan account for 15% and 50% of the stepper motor market, respectively, higher than the United States. Research by MTT analyst Muhammad Mubee indicates that two stepper motor designs dominate FA applications (see the "Market" chart). These are mass-produced tin-can (also known as "can-stack") and permanent magnet stepper motors. Variable reluctance (VR) stepper motors are almost nonexistent. "VR stepper motors have almost no new applications, especially compared to low-cost hybrid stepper motors from China," says Mubeen. VR motors are only used at high temperatures, but their performance is not high. MTT research on "Stepper Motors and Controls in the North American Market (2001-2006)" can be found in the product information center at MotionInfo.com. Berger Lahr Motion Technology (a Schneider Electric company) believes that integration, ease of operation, and networked operation are the main development trends for stepper motors. Reducing the size of the drive and motor helps reduce the need for control cabinets and machine space, and system setup can be completed in less than an hour by setting DIPs and rotary switches, explains project manager Sam Bandy. Stepper drives do not require debugging software. "However, some stepper systems with embedded functions require configuring a software system with a screen for data input," says Bandy. Networkable stepper motors can be driven via open-loop, fieldbus, Ethernet, etc., and can be multi-axis controlled, communicating with higher-level controllers and acquiring system status data. [ALIGN=CENTER] In addition to the high torque due to the stronger magnetic field, Shinano Kenshi's redesigned lamination mechanism for the new stepper motor also provides low magnetic field vibration and a 3-6 dB reduction in noise depending on the operating frequency. [/ALIGN] Competing with servo systems , Bandy points out that the difference between a stepper system combined with a drive motor and servo motion is that it requires no adjustment. "It doesn't require expert tuning and reduces setup time," Bandy says. Another advantage of stepper systems is their fast response speed. Through servo technology, closed-loop PID control, and error correction based on the content of the error, it distinguishes between the preset action and the actual state. "Using passive hysteresis tracking to obtain the reference position is too slow in some applications, such as printing and labeling machines," Bandy says. "In a stepper system, there is no hysteresis. The active response is not dependent on the actual state and can be executed independently by the control." Bergsma of SKC believes the competition between stepper motion systems and servo motion systems lies in the price of the motors. "Servo motors still can't compete with stepper motors in terms of price. Stepper motor prices are constantly falling, while stepper motor prices may never fall," he says. Furthermore, stepper motors themselves have high production volumes, reducing unit costs. "They offer better commercial value than servo motors," Bergsma continues. He refers to the need for "complete operating systems," noting that the number of stepper or servo motors used is limited. Applications using one or two motors typically employ "black box" driver/indexer controllers, sometimes resulting in excessive costs due to their numerous functions. In contrast, "most motors today are integrated into personalized and standardized applications, requiring a large number of motors," Bergsma says. Most motion is driven by stepper systems. These price-sensitive systems leverage the lower production costs of stepper control, using existing driver chips. "Servo drive systems are often used in OEM equipment, but only in small to medium quantities, for closed-loop feedback and acceleration/deceleration, which servos can do," Bergsma adds. Reiterating its point, Connie Chick, Business Director of Control Systems at GE Fanuc, reiterated that stepper systems are only suitable for motion systems where precision is not high and final positioning accuracy is not critical. For simple axes, such as calibration systems for feed rates, guideways, and end-point stops, stepper systems perform well. “Servo motors are high-speed and high-torque. Therefore, stepper systems are not suitable for high-precision and/or high-torque high-speed machines,” Chick said. GE Fanuc focuses on microcontrollers and intelligent stepper motors. It introduces stepper amplifiers, integrated into the machine cover, with commands input via a simple network device. The entire system consists of GE Fanuc’s small, built-in pulse/direction output control 64-bit PLC and MotorCube intelligent stepper motors, taking up no panel space. Intended for low-cost, simple calibration applications, this approach aims to keep the cost of installing a single motion axis below $2,000. “Servo control is still decreasing in price, but simple stepper systems still have a place,” Chick said. GE Fanuc is a supplier of stepper systems and high-performance servo systems. Portescap (a subsidiary of Danaher Motion) also noted the inherent ability of stepper systems to position themselves without feedback when "sized appropriately for the application." This is another advantage over servo motors. "Open-loop control and motor improvements make stepper systems more affordable," notes product manager Dave Beckstoffer. For example, Portescap has significantly increased the output torque of its latest member, the h3 system hybrid stepper motor. The aluminum housing design enhances heat dissipation, thus slowing motor temperature rise and often reducing torque over time. "It also reduces power consumption, benefiting the overall power requirements of the stepper motor system," Beckstoffer explains. The new stepper motor design reportedly uses neodymium magnets to optimize torque density without increasing component size. Sometimes applicable to stackable stepper motors, optimizing torque density in hybrid stepper motors using neodymium iron boron rare-earth permanent magnets is a relatively new approach, according to Beckstoffer. These improvements also help reduce motor noise and resonance. "The bearings of the h3 series motors are protected by a retainer and O-rings to prevent bearing slippage (axial movement during operation), which is a major source of noise during stepper motor operation," Beckstoffe added. Large bearings are used in applications with high slippage and radial loads, similar to standard hybrid stepper motors. [ALIGN=CENTER] According to research by Motion Tech Trends, stepper motion systems in North America are expected to grow by 3-4% in 2006. Portescap's new h3 series hybrid motors offer up to 40% more torque than the same standard h3 motor (a competing product). Stator-reinforced magnets increase torque through concentrated magnetic paths, thus improving performance. [/ALIGN] Applications According to SKC, in applications where encoder closed-loop feedback is not required, such as packaging, material handling, assembly, and where high speed or acceleration/deceleration requirements are not high, stepper motion systems and servo systems compete on an equal footing. "Servo systems perform best in closed-loop applications," Bergsma added. Linear stepper systems compete strongly with semiconductor and fiber optic manufacturing, wire bonding machines, laser trimming machines, wafer probe testing instruments, medical devices, and other applications, Baldor says. Compared to other options, linear stepper systems often win praise for their low maintenance requirements. “In controlled environments where tight axis-to-axis mating is not critical, they are an excellent low-cost solution for any point-to-point application,” adds Feyh of Parker. He cites numerous such applications in life sciences, medical device systems, and other benchtop equipment. MTT cites many examples of tin-can stepper motors used in FAs, such as selection machines, conveyors, and small material handling/packaging machines. Portesca believes stepper motors are favored in the textile industry, electronic assembly, linear stages, and medical analyzer technology. Many stepper motors are also frequently used in larger, more powerful automotive drivetrains. Berger Lahr/Schneider Electric mentions that the target applications for stepper systems include OEM systems requiring low maintenance and low-cost solutions. Machine exporters also prefer stepper systems over servo systems because they require less skill to debug. In summary, stepper-based motion systems remain active in the market. Improvements continue across the entire powertrain industry, but integration and low power consumption remain the most pressing concerns in stepper systems of all sizes.