Automating & Educating the World’s Leading Companies

The Challenge 

Develop a motion control and high speed position feedback module to be used as the basis of a 2-Axis Neuro Otologic test  system to allow researchers and physicians to better understand and diagnose neurological and otological disorders. 

The Solution 

The PCI-7342 2-Axis Stepper/Servo Controller was selected to provide Step and Direction commands to the  drives. This was easily accomplished by choosing to utilize the 7342 in Open Loop Stepper mode. The Yaskawa  drives incorporated a feature to close the position loop internally making it unnecessary to operate the PCI-7342  in closed loop operation. A Universal Motion Interface, UMI-7764, was used to connect the PCI-7342 to the  drives (Figure 1) and counters on a PCI-6229 were used to accurately track the position of the two axes.  

Abstract 

The complex interactions between the human body’s neurological and otological systems are disrupted by disorders and  sometimes simply by unusual body motion. A Neuro Otologic test system is used to test a patient’s inner ear response to  motion by tracking eye response after the body has been moved to various positions or subjected to cyclic motion. The  patient’s response to these motions can indicate specific disorders are present. A motion control and position tracking system  was developed for use as a tool for researchers and physicians. 

Introduction

The motion interface needed to be able to handle two classes of motion, either step motion, or cyclic motion on the Tilt axis.  

These two classes of motion served as the bases of a sequence of positions or protocol. The target positions were transformed  into motion commands that the PCI-7342 Stepper Controller card would to convert to Step and Direction output for the  Yaskawa drives. In prior iterations of this system the client had been converting analog signals with external filters to feed  the Step and Direction inputs to the Yaskawa drives. They required a more flexible and scalable way of providing the  necessary signals to the custom drives. 

The client also had the need for high speed position feedback and display to allow the operator to track the position of each of  the axes in the system. Although the PCI-734 controller is capable of high speed position capture, it is single valued software  timed and required a reset operation which introduced a performance impact that was unacceptable for this particular  application. In order to avoid the adverse performance impact resulting from the resetting of the high speed position capture  feature of the PCI-7340 controller a PCI-6229 counter card was added to the system

Figure 1. Neuro-Otologic Test System 

The application requires the tracking of the angular position of the chair in both axes during the test. This  information needed to be shown on the user interface enabling the test technician to monitor the motion on the  screen. In order to avoid the performance impact associated with resetting of the position register a PCI-6229  Multifunction DAQ board was selected to allow high speed buffered encoder position acquisition. The encoder  signal returned from the Yaskawa drives was fed into the UMI-7764 and also sorted into the 80MHz 32-bit  counter/timer inputs on the PCI-6229. 

DAQmx simplified the creation of two Counter Input Angular Encoder channels, one for the Yaw Axis and one for  the Tilt Axis. These DAQmx channels track the encoder inputs into the PCI-6229 and decode the encoder position as angular outputs. The Z Index input from the encoder resets the angular encoder channel output to  zero degrees. 

Motion can be controlled by the technician using one of two available protocols. The first motion protocol consists  of moving the test subject in a sequence of single axis motion steps. The second motion protocol consists of  moving the test subject in a cyclic pattern on the tilt axis. For this cyclic motion protocol, the motion ramps in  amplitude from a stationary position. 

For the protocol utilizing single axis motion steps, a control input into the motion action engine was developed.  The general multi-step test protocols typically consist of 6-11 individual motion steps. Each step can be described  by six motion parameters (Figure 2): 

• Axis of motion 
• Maximum Velocity, Deg/Sec 
• Acceleration, Deg/Sec²
• Deceleration, Deg/Sec²
• Target Angle, Degrees 
• Motion Direction, Clockwise or Counterclockwise 

These parameters are converted into the units required by the NI-Motion Virtual Instruments, such as “Load  Velocity in RPM.flx”. The power and flexibility of the NI-Motion Virtual Instruments made passing the motion  parameters to the Yaskawa drives very simple and efficient.The tilt axis cyclic motion protocol utilizes the “Absolute Contouring” buffered waveform motion capability of the PCI-7342 card. In Absolute Contouring mode the controller smoothly splines through the motion described by the  

Figure 2. Motion Control Parameters 

target waveform. The operator creates a motion profile using a previously developed cyclic motion protocol editor.  The output of this protocol editor is a waveform that describes the tilt axis motion in target degrees versus time.  The waveform target angles are converted from degrees to motor steps and then loaded into a buffer on the  motion card. The motion is then initiated on the tilt axis using the buffered position information. 

Summary 

This application greatly simplifies the client’s hardware set up, removing the need for external filters to convert  analog motion commands to step and direction information required by their drives. It also allows the use of the  NI-Motion suite of VI’s, simplifying the motion control operation. The use of the PCI-6229 80 MHz 32-bit counter  channels along with DAQmx allows the operator to precisely track the motion. The use of the PCI-6229 also  overcomes the sample rate limitation of the high speed position read function of the PCI-7342 Motion Controller.