# Evaluation of the Large-Length Indoor Standard Installation Based on Single Point Scanning
## 2 Measurement Platform  
LLISI is composed of the guide system, the spatial triangular laser length measuring system, the real-time environment parameter correction system, the control system, the targeting and image acquisition system and the data processing system. The first linear guide LLISI in China that was developed by our institution is shown in Figure 1b. The length of the linear guide was about 57 m, and the two guides were placed on a granite bearing platform, with a distance of about 600 mm and an approximate height of 1.3 m. The laser tracker was aimed at the optical target mirror [17] on the LLISI, which was fixed on the platform via magnetic force. According to the loading conditions, the bearing platform was controlled to move forward, and the coordinates in the coordinate system of the laser tracker were recorded. Since the relative spatial position between the optical target mirror and the measuring platform remained constant, the speed, displacement and positioning accuracy of the optical target mirror directly reflect the motion parameters of the LLISI platform. The control system of LLISI includes the software control system and the electrical control system. In the software control system, the 60-meter LLISI software based on the Labview environment can indirectly implement the function of the electrical control system, and can set the parameters such as the velocity of the measurement system, time and so on. There are some function modules for controlling the system and monitoring the status of system in the software, including experimental environment monitoring, operation status monitoring of the stress system, the electric control system trigger and data acquisition. The electrical control system is composed of a power supply control system, control handle, and bed electrical module (such as drive motor, sensor, limit switch, etc.). Pulse width modulation (PWM) method is utilized to control the DC motor drive of \(x\)-axis for modulating the movement mode of Sanyo motor. In order to accurately control the measuring platform, the PWM method can not only reduce 2-axis inertia but also enhance the response rate of motor. In addition, controlling the initial value of timer of microprocessor can transform the input analog control signal to the digitally coded signal to implement the PWM method. It can instantly generate pulse waveforms with different duty ratios, thereby achieving the adjustment of the average speed of the platform. The average speed of the continuously adjustable measuring platform ranged from 0 to 200 mm/s, which can be calculated by the following equation: In order to accurately control the measuring platform, the PWM speed control system was used to adjust the speed of the electric platform of LLISI. The initial value of the internal timer of the single-chip computer was adjusted to generate pulse waveforms with different duty ratios, thereby achieving the adjustment of the average speed of the platform. The average speed of the continuously adjustable measuring platform ranged from 0 to 200 mm/s, which can be calculated by the following equation:  
The average speed of the measuring platform:  
\[\mathrm{V_{d}}=\mathrm{V_{max}}\cdot\frac{\mathrm{t_{1}}}{\mathrm{T}} \tag{1}\]  
\[\mathrm{t_{1}}=(2^{\mathrm{n}}-\mathrm{T_{\omega}})\times\frac{\mathrm{N}}{ \mathrm{f}\times 10^{6}} \tag{2}\]  
where \(\mathrm{V_{d}}\) is the average speed of the motor, \(\mathrm{V_{max}}\) is the maximum rotational speed of the motor, \(\mathrm{t_{1}}\) is the length of the timer, \(\mathrm{T_{\omega}}\) is the initial value of the timer, N is the clock value in one machine cycle, \(\mathrm{f}\) is the clock frequency of the single-chip computer. As shown in Figure 1a, the specific steps of the method are as follows:  
1. An optical target mirror for aiming of the laser tracker was installed on the LLISI.