When it comes to achieving high resolution in motion control applications, there is more than one way to skin the cat. In their quest to push resolution as far as possible, manufacturers of interface boards, encoders, A/D converters, and drives are pursuing a variety of different strategies. Here's a look at some of the newest offerings.
|For a helpful handbook on motion control, including a discussion of feedback devices developed by MicroMo Electronics, go to http://rbi.ims.ca/4391-550.
True Absolute Encoders
Gurley Precision Instruments A58 Absolute Encoder is a single-turn absolute rotary encoder available with 12-, 14-, 15- and 16-bit resolution. The optical sensor's code disk is etched chrome on glass. The unit has a nonoperating slew of 10,000 rpm. Output formats include serial and multiplexed versions of Gray code or natural binary for higher resolution models. The accuracy of these units is ±1 LSB. The 12-bit model also has a parallel output format and its accuracy is ±0.5 LSB. The maximum rotational speed for valid code is 30 rpm for all units. The 58-mm diameter unit comes with a 3-mm to 0.25-inch diameter stainless steel shaft.
For more information on Gurley Precision Instruments A58, go to http://rbi.ims.ca/4391-549.
Sinusoidal Encoder Interpolation Interface Board
Galil Motion Control's DB-28104 board interpolates the output of up to four sinusoidal encoders delivering higher position feedback resolution without using an ultra high-resolution encoder. Used in conjunction with any of the Galil amplifier boards, once an axis is controlled using a sinusoidal encoder, the maximum allowable speed and acceleration settings are increased to 50 million counts per second, and 109 counts/sec2 respectively. With the DB-28104, position tracking occurs at two levels. Similar to a quadrature encoder, the unit counts coarse cycles. For higher resolution, bit-wise interpolation of the two sinusoidal signals provides the precise position inside the cycle. The user establishes the interpolation rate, which ranges from 25 through 212 points per sinusoidal cycle. The unit accepts both single-ended and differential encoder inputs, as well as differential index signal inputs.
For more information on Galil Motion Control's DB-28104, go to http://rbi.ims.ca/4391-546.
All Digital Industrial Drive
Danaher Motion's Kollmorgen S200 series brushless servo drives are all digital industrial units with a velocity loop bandwidth up to 800 Hz providing increased system throughput and simplified tuning. To achieve smooth motion and rapid start and stop action for optimized machine performance, the units have 24-bit resolution and 3-5 kHz current loop bandwidth. Using smart feedback and high bandwidth facilitates "plug and play" commissioning by eliminating the need for servo loop tuning in most applications. The units feature optically isolated inputs/outputs, positive locking connectors, full fault protection, and separate keep-alive power input. The drives come standard with torque or velocity control and optionally support Indexing, CANopen, or DeviceNet. The servo control units target applications in semiconductor fabrication, electronic assembly, packaging, medical, and woodworking equipment. For more information on Danaher Motion's Kollmorgen, go to http://rbi.ims.ca/4391-547.
12-Bit Motor Control A/D Converter
With a maximum sample rate of one million samples per second (MSPS), Texas Instruments ADS7869 provides 12-bit resolution. Designed specifically for demanding motor control applications, the ADS7869 integrates three analog-to-digital converters (ADCs) with a total of seven sample-and-hold capacitors and 12 differential input channels. The unit has four sign comparators connected to four input channels and three additional fully differential inputs. The ADS7869 has a parallel port that can be configured to different standards, a serial peripheral interface (SPI), and a specialized serial interface with three data lines for VECANA01 mode. This allows the ADS7869 to interface with most digital signal processors or microcontrollers. To ensure that the analog input of the encoder is held at the same point of time as the counter value, the chip integrates two up-down counters to analyze the position sensor data. For more information on Texas Instruments ADS7869, go to http://rbi.ims.ca/4391-548.