Rack-and-Pinion Page 1 of 5

Gurley Precision Instruments IIIIIIIIIIIIIIII

ISO 9001 Certified Motion type: Usage: Output: Max. resolution:

Linear Industrial Incremental 5 µin

Rack and Pinion Linear Measuring Systems

Benefits and Features

The System

•

High resolution (to 5 µin)

•

High speed (to 80 in/s)

•

Easy installation

•

Unlimited measuring length

•

Completely sealed encoder

•

Relatively insensitive to contamination

Gurley Rack-and-Pinion Systems are based on the use of high precision rack, meshing with a pinion that drives an incremental optical encoder. They provide an effective means of measuring linear position or speed over unlimited lengths. The salient benefits of such a system include good tolerance to misalignments due to installation or machine geometry variances, high resolution with commensurate accuracy, long life and relative insensitivity to contamination.

As part of our continuing product improvement program, all specifications are subject to change without notice.

514 FULTON ST • TROY, NY 12181 • PHN 800-759-1844 • 518-272-6300 • FAX 518-274-0336

www.gurley.com

[email protected]

Rack-and-Pinion Page 2 of 5

Gurley Precision Instruments IIIIIIIIIIIIIIII

ISO 9001 Certified

The Rack The precision racks are ground from type 416 stainless steel and heat-treated to 35-40 Rc hardness. Each rack section is 12 inches long and has a full tooth at each end. This feature allows the racks to be butted with adjustable gaps to keep the rack error from accumulating from one section to the next. The helicoidal tooth form provides very good pitch accuracy and reduces the necessity for precise alignment of the pinion. The rack is available in standard Grade 2 and high-accuracy Grade 4. Grade 2

Grade 4

Model number

AX00107

AX00780

Max peak error

0.001 (0.025)

0.0003 (0.008)

Max error about end datum,

±0.0005 (±0.0125)

±0.00015 (±0.004)

Adjacent tooth-to-tooth error

0.0004 (0.01)

0.0001 (0.0025)

+0, -0.0007 +0, -0.0005 (+0, -0.018) (+0, -0.013) Note: Values are per 12-inch section. All dimensions in inches (mm). Pitch height variation

Rack can be purchased in individual sections, as described above, for mounting directly onto the user’s equipment. It is also available housed in a heavy-duty aluminum extrusion with rubber sealing flaps; this provides protection against mechanical damage, resistance to contamination and easier installation. Housings are fabricated in one-foot increments up to 13 feet long. For travel over 13 ft, two or more housings are easily joined together. The actual available working length of a housed assembly is one inch less than the overall length. To order a housed rack assembly XXX inches long with Grade 2 or Grade 4 rack, specify 8795XXXB or 8796XXXB, respectively. (XXX must be a multiple of 12.) Individual rack sections weigh 0.44 lb/ft (6.4 N/M); housed rack assemblies weigh 3.8 lb/ft (55.5 N/m). After either the housed rack assembly or individual rack sections are installed, they can be “tapped in” using a laser interferometer or other calibration device so that the rack error does not accumulate as the pinion travels from section to section. This procedure is not mandatory, but it can be used when the application requires the best obtainable accuracy. The Pinion The pinion is precision-hobbed as an integral part of the encoder shaft. This improves accuracy by eliminating eccentricity and other errors that result from attaching a separate pinion. Like the rack, the pinion is made from hardened type 416 stainless steel to minimize wear. There are two pinion shafts available: shaft code P is a 10-tooth pinion that traverses one inch of rack per revolution; code Q is a 20-tooth pinion that traverses two inches per revolution. The total composite pinion accuracy is ±0.000175 in (± 0.0045 mm), which conforms to AGMA Q15 standards. This error is not cumulative, but it repeats every inch (or two).

514 FULTON ST • TROY, NY 12181 • PHN 800-759-1844 • 518-272-6300 • FAX 518-274-0336

www.gurley.com

[email protected]

Rack-and-Pinion Page 3 of 5

Gurley Precision Instruments IIIIIIIIIIIIIIII

ISO 9001 Certified

The Encoder Gurley’s Series 9x25 is a family of industrial-grade optical incremental encoders that is available in two models: 9125 and 9225; they are mechanically the same, but they differ in their accuracy and interpolation capabilities. (There is also a very-high-accuracy 9425, but it’s not usually required on rack-and-pinion systems.) When they are provided with an integral pinion shaft, they become models 9125P and 9225P (with the 10-tooth, 1in/rev pinion) or 9125Q and 9225Q (with the 20-tooth, 2-in/rev pinion). Please refer to the Series 9x25 data sheet for complete encoder specifications. Flex-Mount Bracket The optional encoder mounting bracket incorporates a spring flexure, which ensures constant contact between the pinion and the rack; this reduces backlash error to less than 0.00002 in (0.0005 mm). There is a pre-load adjustment screw to compensate for installation tolerances. To order, specify Model 37721. System Resolution With our wide choice of line counts on the disc and electronic interpolation options, many linear resolutions can be achieved. The following table shows some typical combinations, but others are also available. FINAL RESOLUTION is after 4X quadrature decoding in the customer’s electronics. ENCODER MODEL

LINE COUNT

INTERPOLATION FACTOR

FINAL RESOLUTION

MAX SPEED

9225P

5000

10

0.000 005 in

10 in/s

9225P

2500

10

0.000 010 in

20 in/s

9225P

2500

5

0.000 020 in

24 in/s

9225P

2500

2

0.000 050 in

30 in/s

9125P

2500

1

0.000 100 in

80 in/s

9125P

1250

1

0.000 200 in

80 in/s

9125P

500

1

0.000 500 in

80 in/s

9125Q

500

1

0.001 000 in

80 in/s

9225P

2540

10

0.000 250 mm

500 mm/s

9225P

2540

5

0.000 500 mm

600 mm/s

9225Q

2540

5

0.001 000 mm

1200 mm/s

9125P

2540

1

0.002 500 mm

2000 mm/s

9225Q 2540 1 0.005 000 mm 2000 mm/s Note: Max speeds up to 80 in/s (2000 mm/s) are based on encoder frequency response limit. For speeds between 40-80 in/s (1000-2000 mm/s), a lubricant such as MoS2 paste is required between the rack and pinion. 514 FULTON ST • TROY, NY 12181 • PHN 800-759-1844 • 518-272-6300 • FAX 518-274-0336

www.gurley.com

[email protected]

Gurley Precision Instruments IIIIIIIIIIIIIIII

Rack-and-Pinion Page 4 of 5

ISO 9001 Certified

Accuracy The total error from all the rotating components (encoder accuracy plus total composite pinion error plus pinion runout) is less than 0.0005 in (0.013 mm). This error does not accumulate, but it repeats every inch. For total system error, this rotating component must be added to the rack error and the backlash. If the rack has been “tapped in” so that its error does not accumulate from section to section, then the sum represents the total system error regardless of length of travel. No allowance has been made for machine geometry errors. Installation The rack-and-pinion system with the housed rack has been designed for easy installation on most types of host machines. Detailed mounting instructions are included with each system. The housing assembly includes a mounting spar, which is installed on the host machine and adjusted for proper alignment. The rack housing is then secured to the mounting spar. The rubber sealing flaps are pressed into place, and the encoder is mounted with the pinion properly positioned and engaged with the rack. With the Flex-Mount Bracket, the correct pre-load is set and the installation is complete.

514 FULTON ST • TROY, NY 12181 • PHN 800-759-1844 • 518-272-6300 • FAX 518-274-0336

www.gurley.com

[email protected]

Rack-and-Pinion Page 5 of 5

Gurley Precision Instruments IIIIIIIIIIIIIIII

ISO 9001 Certified

Ordering information Individual 12-in sections

Housed assembly, XXX in long

Grade 2 Rack

AX00107

8795XXXB

Grade 4 Rack

AX00780

8796XXXB

Flex Bracket 37721 Encoder

See Series 9x25 Data Sheet for encoder ordering information

Special Capabilities For special situations, we can optimize encoders to provide higher frequency response, greater accuracy, wider temperature range, reduced torque, non-standard line counts, or other modified characteristics. In addition, we regularly design and manufacture custom encoders for user-specific requirements. These range from high-volume, low-cost, limited-performance commercial applications to encoders for high-performance, highreliability conditions. We welcome the opportunity to help you with your special encoder needs. Warranty Gurley Precision Instruments offers a limited warranty against defects in material and workmanship for a period of one year from the date of shipment.

24-Jun-02

514 FULTON ST • TROY, NY 12181 • PHN 800-759-1844 • 518-272-6300 • FAX 518-274-0336

www.gurley.com

[email protected]