Technical Specifications

Technical Details:

Configurations: 12 standard, 16 with optional 3^rd mass, 18 with second drive acce4ssory

Dynamics: 2^nd, 4^th and 6^th ( 3 mass option) order, Systems type 0, 1 and 2

I/O: SISO, SIME, MIMO (with sec. drive accessory)

Poles and Zeros: Adjustable 1.5 ~ 7 Hz

Mass Adjustment Ratio: 5:1

Spring Adjustment Ratio: 2:1

Size: Bench-top, 31x92x15cm

Feedback: High res. encoders, 1600 counts/cm

Actuator: 8 N rack & pinion, Fe-Co brushless motors

Servo Amplifiers: 5 KHz current loop bandwidth

Technical Specifications

The mechanism shown in Figure1 is designed to emulate a broad range of real-world applications including 1 DOF rigid bodies, flexibility in linear drives, gearing and belts, and other coupled discrete oscillatory systems. The apparatus, shown in Figure1, consists of two or three mass carriages interconnected by bi-directional springs. The mass carriage suspension is an anti-friction ball bearing type with approximately ± 3 cm of available travel. The linear drive is comprised of a gear rack suspended on an anti-friction carriage and pinion (pitch dia. 7.62 cm (3.00 in)) coupled to the brushless servo motor shaft. Optical encoders measure the mass carriage positions – also via a rack and pinion with pinion pitch dia 3.18 cm (1.25 in)1.

Figure 1 Rectilinear Apparatus

Springs of various stiffness may be attached between the masses and the base plate. A dashpot with adjustable damping may be coupled to any of the masses. Position measurement scales are provided to assist in certain experiments and system setup.

Changing Plant Configurations and Parameter Values

The plant may be placed in a variety of spring/mass/damper configurations with 1, 2, and 3 degrees of freedom (DOF). Springs may be mounted interchangeably and are supplied in two nominal stiffnesses: 450 N/m (2.25 lb/in), and 800 N/m (4.5 lb/in).

The dashpot connects to any of the mass carriages either through direct attachment or via the extension bracket. The damping constant may be varied by adjusting the air flow valve on the rear of the dashpot. Coarse adjustments are made via the knurled knob and fine adjustments via the metal screw.

It is possible to change inertia values by changing the number of brass weights (500± 5g each). It should be made certain that the weights are firmly clamped by the thumb nut before operating or transporting the mechanism.

The travel limit stops must also be set before operating or transporting. The stop assemblies include a rubber “bumper” to physically stop the motion, and a limit microswitch set to engage prior to the stop tab contacting the bumper. When a given mass carriage is intended to have free motion, the limits should generally be set to ± 3 cm. Whenever the stop positions are moved, the user should verify that they are securely fastened in their new position. It should also be checked that the limit switches engage (“click” sound) prior to contacting the bumper, and that they are contacted prior to interference between any other mechanical elements (e.g. that the encoder cable ends do not travel beyond their pulley). For some plant configurations, the second or third mass must be clamped. In this case a shim (e.g. a 1/4 in. threaded nut) must be placed between the bumper and the stop tab to ensure that the corresponding limit switch is not engaged.

Hardware/Software

By enter the ‘Sci-Cal’ program by double clicking on its icon you should see the Background Screen. Gently move the first mass carriage by hand. You should observe some following errors and changes in encoder counts. The Control Loop Status should indicate “OPEN” and the Controller Status should indicate “OK”.

Make sure that you can oscillate the mass carriages freely. Now press the black “ON” button to turn on the power to the Control Box. You should notice the green power indicator LED lit, but the motor should remain in a disabled state. Do not touch the apparatus whenever power is applied to the Control Box since there is a potential for uncontrolled motion of the masses unless the controller has been safety checked.